EXTRACTION, OPTIMIZATION AND

ETHIOPIAN MARULA (

(PODOCARPUS FALCATUS)

A Thesis Submitted to the School of Chemical and Bio

Fulfillment of the Requirements for the Degree of Master of Science in Chemical

Engineering Stream of Food Engineering of Addis Ababa University

Advisor: Dr Abubeker Yimam (Assistant Professor)

Co-Advisor: Dr Sisay Feleke

PTIMIZATION AND CHARACTERIZATION OF

ARULA (SCLEROCARYA BIRREA

ODOCARPUS FALCATUS) OILS

By

Gadissa Hundessa

A Thesis Submitted to the School of Chemical and Bio-Engineering in Partial

Requirements for the Degree of Master of Science in Chemical

Engineering Stream of Food Engineering of Addis Ababa University

Advisor: Dr Abubeker Yimam (Assistant Professor)

Advisor: Dr Sisay Feleke

Addis Ababa, Ethiopia

2014

HARACTERIZATION OF

CLEROCARYA BIRREA) AND ZIGBA

ILS

Engineering in Partial

Requirements for the Degree of Master of Science in Chemical

Engineering Stream of Food Engineering of Addis Ababa University

Advisor: Dr Abubeker Yimam (Assistant Professor)

i

ADDIS ABABA UNIVERSITY

INSTITUTE OF TECHNOLOGY SCHOOL OF

CHEMICAL AND BIO-ENGINEERING

EXTRACTION, OPTIMIZATION AND CHARACTERIZATION OF

ETHIOPIAN MARULA (SCLEROCARYA BIRREA) AND ZIGBA

(PODOCARPUS FALCATUS) OILS

A THESIS SUBMITTED TO THE SCHOOL OF CHEMICAL AND BIO-ENGINEERING,INSTITUTE OF TECHNOLOGY, ADDIS ABABA UNIVERSITY, IN PARTIAL

FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

IN CHEMICAL ENGINEERING (FOOD ENGINEERING STREAM)

BY: GADISSA HUNDESSA

Approved by the Examining Board Signature Date

Mr. Taye Zewdu __________ __________(PG Coordinator at School of Chemical and Bio Engineering)

Dr. Abubeker Yimam (Assistant. Prof) __________ __________ (Advisor)

Dr. Sisay Feleke __________ __________(Co-Advisor)

Eng. Gizachew Shiferaw __________ __________(Internal Examiner)

Dr. Eng. Shimelis Admassu (Associate. Prof) __________ __________(External Examiner)

ii

ACKNOWLEDGMENTS

First of all I would like to thank Almighty God, the source of all knowledge and

wisdom. I am grateful to my advisor Dr Abubeker Yimam and co-advisor Dr Sisay

Feleke for their patience and encouragement through kind e-mails and phone calls

starting from the beginning of the work; the support and guidance in the manuscript

writing as well as for their inspiration, advice, and countless support during

conducting this thesis work. In addition to that, I would like to sincerely appreciate

their positive attitude and result oriented personality.

I have indescribable grateful thanks to all my friends, especially Mr. Yohannes Tolesa,

Mr. Yonas Assefa and Mr. Cherenet Tefera for their encouragement, and inestimable

support.

I am also very thankful to Kebron Food Complex and Booez Food complex P.L.C.

staffs, for their valuable support, advice and comments. Also special thanks to Mr.

Bisrat Tadesse (General Manager of Kebron Food Complex), Mr Abrham (Chief

Warden of Nech Sar National Park) and Professor Hinsermu for their invaluable

supports to complete this project.

I am really grateful to my family and friends. As well all others who directly and

indirectly contributed to this document in general, for their encouragement, support

all the time, and voluntary involvement, the assistance and help I received in using

whatever resource they have.

iii

ABSTRACT

To investigate the potential use of marula (Sclerocarya birrea) and Podocarpus falcatus oil

and to recommend the optimum extraction conditions, dried podo and marula seeds

were crushed to release the kernels and oil was extracted using n-hexane as a solvent

for 2, 3 and 4 hours with moisture content of 9%, 12% and 15%. Main characteristics of

optimized oil extract were determined. The average oil content was found to be

61.36% and 58.63 % respectively for S. birrea and P. falcatus with optimum extraction

conditions of 12% moisture content and 3 hours of extraction. The saponification value

of the oils were 190 mg KOH/g and 189.1 mg KOH/g oil, specific gravity at 150C was

0.899 and 0.90, peroxide value 4.2 and 4.4 mEq/kg, refractive index 1.467 and 1.47

whilst the average acid value was 3.6% and 4.0% respectively for S. birrea and P.

falcatus oils. The fatty acid profile of S. birrea and P. falcatus oils were determined using

GC-M S. Oleic acid was found to be the predominant fatty acid, 73.60% and 78.94%

respectively for S. birrea and P. falcatus oils. Analysis of the main characteristics

indicated that both S. birrea and P. falcatus oils have potential use in salad, cooking oils

and cosmetics application. Marula juice was extracted and characterized. The result

showed 25% of marula fruit can be extracted to juice. The juice is rich in vitamin C,

141.29 mg/100g and potassium 257.2mg/100g.

Key words: Sclerocarya birrea, Podocarpus falcatus, Fatty acids profile, Optimum,

moisture content, extraction time, effect

iv

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE PAGE….…………………………………………………………………………………….i

ACKNOWLEDGEMENTS…..……………………………………………………………….….ii

ABSTRACT.....................................................................................................................................iii

TABLE OF CONTENTS.……………………..……………………………………………........iv

LIST OF TABLES…………………………………………..…………………………………….vi

LIST OF FIGURES……………………………………………………..…………………..…....vii

LIST OF ABBREVATIONS……………………………………………………….…………...viii

LIST OF APPENDICES………………………………………………………………………....ix

I. INTRODUCTION.......................................................................................................................... 1

Background ................................................................................................................................... 1

Statement of the problem ............................................................................................................ 3

Objectives of the study................................................................................................................. 5

General objective ............................................................................................................. 5

Specific objectives............................................................................................................ 5

Significance of the study.............................................................................................................. 5

II. LITERATURE REVIEW ................................................................................................................ 6

2.1 Oil and fat structure ........................................................................................................ 6

2.2 Importance of oils............................................................................................................ 6

2.3 Physicochemical characteristics of plant oil and Fatty Acid composition .............. 8

2.3.1 Specific gravity..................................................................................................... 8

2.3.2 Moisture Content................................................................................................. 8

2.3.3 Saponification value............................................................................................ 9

2.3.4 Oil acidity ............................................................................................................. 9

2.3.5 Fatty acids........................................................................................................... 10

2.4 Sclerocarya birrea (Marula) ............................................................................................ 15

2.4.1 The Marula tree and its fruit ............................................................................ 15

2.4.2 The use of marula .............................................................................................. 16

2.4.3 Nutritional Status .............................................................................................. 19

2.4.4 Food items based on Pulp, Skin and Juice ..................................................... 25

2.4.5 Items based on kernels...................................................................................... 28

2.5 Podocarpus falcatus.......................................................................................................... 29

v

III. MATERIALS AND METHODS................................................................................................ 31

3.1 Materials ........................................................................................................................... 31

3.1.1 Study sample................................................................................................................... 31

3.1.2 Equipment and Data Collection ................................................................................... 31

3.2 Frame work of the experiment ....................................................................................... 31

3.3 Methods................................................................................................................................ 33

3.3.1 Sample preparation ............................................................................................. 33

3.3.2 Proximate Analysis ............................................................................................. 35

3.3.3 Sample Analysis (Gas Chromatography-Mass Spectrometry) ..................... 42

IV. RESULTS AND DISCUSSION ................................................................................................. 43

4.1 Marula Juice Extraction and Proximate analysis ...................................................... 43

4.2 Determination of moisture content............................................................................. 46

4.3 Preliminary work........................................................................................................... 46

4.3.1 Selection of particle size.................................................................................... 46

4.4 Soxhlet Extraction.......................................................................................................... 47

4.4.1 Percent yield of soxhlet extractor .................................................................... 47

4.4.2 Effect of extraction time on percent yield of oil ............................................ 48

4.4.3 Effect of particle moisture content on oil yield ............................................. 50

4.5 Physico-chemical characteristics ................................................................................. 56

4.5.1 Specific gravity................................................................................................... 56

4.5.2 Refractive Index................................................................................................. 57

4.5.3 Viscosity.............................................................................................................. 57

4.5.4 Acid value and free fatty acids ........................................................................ 58

4.5.5 Saponification value.......................................................................................... 58

4.5.6 Peroxide value.................................................................................................... 59

4.5.7 Fatty acid composition...................................................................................... 60

V. CONCLUSIONS AND RECOMMENDATIONS.................................................................. 62

5.1 Conclusions .................................................................................................................... 62

5.2 Recommendations......................................................................................................... 63

REFERENCES.......................................................................................................................................... 64

APPENDICES………………………………………...……………………………….……………..…72

vi

LIST OF TABLES

Table Title Page

2.1 Oil content and characteristics of oils from some crops plants......................................................... 10

2.2 Names and descriptions of some fatty acids found in biological materials.................................... 12

2.3 Fatty acid composition of some crop plants ........................................................................................ 14

2.4 Nutritional composition of pulp and kernel........................................................................................ 21

2.5 Amino acid composition of S.birrea kernel meal, kernels and, fruit flesh (g/100 g protein)........ 22

2.6 Physicochemical characteristics of Sclerocaryabirrea kernel oil.......................................................... 22

2.7 Principal fatty acids of Sclerocarya birrea fruit flesh, kernel, kernel oil, and olive oil..................... 23

2.8 Composition of marula beer .................................................................................................................. 24

2.9 Concentrations of mineral elements &fermentation products of home-made marula wine........ 25

3.1 AOAC 2000 Mineral content analysis methods .................................................................................. 41

4.1 Proximate analysis of marula juice ....................................................................................................... 43

4.2 Particle size determination…...…………..…………………………………………………...44

4.3 Total % yield for soxhlet extractor for different m.c. and extraction times…………...…48

4.4 ANOVA results for an experiment in soxhlet extraction of marula oil……………….....51

4.5 ANOVA results for an experiment in soxhlet extraction of P. falcatus oil……………….51

4.6 Difference between the actual (experimental) value and predicted value for marula oilyield…...………………………………………………………………………………………..54

4.7 Difference between the actual (experimental) value and predicted value for P. falcatusoilyield…...……………………………………………………………………………………55

4.8 Physico - Chemical properties of S. birrea (marula) and P. falcatus oil…………………...56

4.9 Fatty acid composition of S. birrea (Marula) and P. falactus oils…………………………..61

vii

LIST OF FIGURES

Table Title Page

2.1 (A) Marula tree and (B) Marula tree bark...................................................................................15

2.2 Marula fruits (A) and squeezing marula juice (B).....................................................................17

2.3 Marula stone cracked (A) and extracting its kernel (B)............................................................17

2.4 Mini marula festival........................................................................................................................18

2.5 P. falcatus (A) Fruit (B) Dried seed................................................................................................30

3.1 Frame of the experiment…………………………………………………………………………32

3.2 Marula (a) fruit (b)from left to right: juice, nut and pulp……………………………….........33

3.3 Methods for cracking marula nut (a) stone crushing (b) metal cutter……………………….33

3.4 Sorted and cleaned podocarpus falcatus seed……………………………………….…………...34

3.5 Ground and Sievedpodocarpusfalcatusseed……………………………………………………...34

4.1 The effect of time on marula oil yield at moisture content (a)9%, (b)12% and (c)15%..........49

4.2 The effect of time on P. falcatus oil yield at moisture content (a)9%, (b)12% and (c)15%......50

4.3 Effects of time, moisture content and their interactions on (a) marula (b) P. falcatusoil yield……………………………………………………………………………………………52

4.4 Predicted vs. actual value of yield for soxhlet extraction (a) marula oil (b) P. falcatus oil...53

viii

LIST OF ABBREVIATIONS

A.O.A.C Association of Official Analytical Chemists ALA α-linolenic acidAAS Atomic absorption spectroscopy ANOVA Analysis of variance AV Acid value d.w Dry weight DHA Docosahexaenoic acidEPA Eicosapentaenoic acidFA Fatty acidFAME Fatty acid methyl esters FAO Food And Agriculture OrganizationFDA Food and Drug Administration FFA Free fatty acids FRC Forestry Research CenterGC-MS Gas chromatography Mass SpectrometryLCFA Long-chain fatty acidsM.C. Moisture ContentMP Melting PointMUFA Monounsaturated fatty acidsNRC National Research CouncilNRI National Resource Institute NTFP Non Timber Forest ProductsP. falcatus PodocarpusfalcatusPUFA Polyunsaturated fatty acids PV Peroxide value RF Resilience Foundation RI Refractive index S. birrea SclerocaryabirreaSD Standard deviation SFA Saturated fatty acidsSG Specific gravity SV Saponification value Uns Unsaponifiable matterWHO World Health Organizationw.b Wet basisVit Vitamin

ix

LIST OF APPENDICES

Appendix Title Page

I Vitamin C content of marula fruit in comparison to some fruits………..............73

II Sample collection, pretreatments and laboratory work…………..………...........74

III GC-MS analysis (A) Podocarpusfalcatus (B) Sclerocaryabirrea…..……….................76

1

CHAPTER ONE

INTRODUCTION

Background

Ethiopia is known for its biodiversity resulted of its wide geographical location. This

makes it to have abundant wild plants and cultivated native trees species with great

silvicultural and commercial potential as food tree crops, oil tree crop and industrial

tree crop. In most case, the forests and woodlands are excellent sources of food,

medicine, energy source and other uses. Local communities collect fruits, seeds, tubers,

leaves to supplement regular nutrition. Collected products also form first-rate fallback

during times of famine or in the case of natural disasters (NRC 2008). Fruits and nuts

are rich in vitamins and minerals with qualities that can become desirable sources of

nutrition and as a supplement for growing children and mothers. In addition, they are

marketable commodities in the local markets often contribute considerable income for

household economy. (P. fund & Robinson, 2005)

Worldwide, natural vegetable oil and fats are increasingly becoming important in

nutrition and commerce because they are sources of dietary energy, antioxidants,

biofuels and raw material for the manufacture of industrial products. They are used in

food, cosmetic, pharmaceutical and chemical industries. Vegetable oils account for 80%

of the world’s natural oils and fat supply (FAO, 2007). With increasing awareness of the

importance of vegetable oils in the food, pharmaceutical and cosmetic industries, there

is need to increase the amount of oil produced in order to meet the increasing demand.

Forests are also potential sources of both edible and industrial vegetable oil. Of course,

the forests Ethiopia are endowed with a number of high value tree spices which have

higher potential to produces, other than timber, the non-timber products like oil, gum,

resin, latex and others. Among the oil bearing tree species of Ethiopia, Sclerocarya birrea,

and Podocarpus falcatus (syn = Afrocarpus falcatus), can be mentioned as an example here.

So utilization of these oil bearing tree species will not only reduce the nation

2

expenditure of the country foreign currency through import substitution but also

improve the livelihood of the rural people through availing healthy edible oil, maintain

the environmental balance and improving household income.

Generally, oils and fats from seeds and nuts constitute an essential part of man’s diet.

Fats and oils, together with proteins, carbohydrates, vitamins and minerals, are the

main nutrients required by the human body. Fats and oils are rich sources of energy,

containing two and a half times more calories than carbohydrates (per unit weight). In

addition to being a source of vitamins A, D, E and K, fats and oils also contain essential

fatty acids. These essential fatty acids are not manufactured by the body and must be

obtained from diets, with linoleic, oleic and linolenic acids as examples of unsaturated

fatty acids (NRI, 1995).

Modern processing of vegetable oils yields valuable products such as oleo chemicals.

Oleo chemicals are now largely being used as ingredient in the manufacture of many

industrial products, namely building auxiliaries, candles, detergents and cleaning

agents, cosmetics, fire-extinguishing agents, flotation agents, food emulsifiers,

insecticides, lubricants, paints, paper, medicine and chemicals. The meal or cake is used

in the formulation and preparation of livestock feeds and food additives. The purpose

of this study is to exploit the potential use of P. falcatus and S. birrea (marula) as an

edible oil.

3

Statement of the problem

In Ethiopia, woodland and dry land forests are important source of a variety of non-

timber forest products (NTFPs) such as gums and resins, and beeswax, medicinal and

aromatic plants, dying and tanning materials and in some situations, NTFPs account for

a significant share of household income, this is still remained with great-undeveloped

potential for improving incomes for the local community around the forest and

woodland itself without degrading the resources.

Sclerocarya birrea (marula) is one of dry land African fruit trees. In Ethiopia, the

species found in open deciduous woodlands on rocky slopes in dry and moist agro-

climatic zones of western Tigray, Shewa, Gambella, GamoGofa, Borena and Sidamo in

an altitudinal range of 400-1700mm (Azene 2007).

The fruits are rich in vitamin C, about five times higher than that of the citrus fruit

(Leakey, 1999). The fruit pulp are eaten fresh, boiled to a thick black consistency for

sweetening porridge or fermented to make alcoholic drinks of both local and

commercial value (Maundu et al., 1999; Leakey, 1999; Agufa, 2002). In famine years, the

kernel is locally roasted and eaten. At dry matter kernel has 57.3% fat, 28.3% protein,

6% total carbohydrates, 2.9% fiber, and rich in phosphorus, magnesium and potassium

(Glew et al., 2004). The fruit is also used to make juice, jam, jellies and as a cosmetic

agent (Leakey, 1999; Shackleton et al., 2002). The leaves and bark have medicinal

properties (Kokwaro, 1976).

Marula has acquired significant commercial importance since its fruits and other

products entered local, regional and international trade in the Southern Africa region

(Shackletonet al., 2002; Phofuetsile and O’Brein, 2002). The pulp is used to extract

popular commercial alcoholic drinks sold under different trade names. The fruit is

edible and contains an exclusively hard endocarp with 0 to 4 kernels (Leakey, 2005) that

have considerable commercial value in the South African region as nutmeat. There are

no reports on commercialization of the species in Ethiopia.

4

Podocarpus falcatus (Afrocarpus falcatus) occurs in mountain forest from Ethiopia through

Kenya, Tanzania and Mozambique to eastern and southern South Africa; also in

Swaziland and Lesotho

The wood, often traded as 'podo' or 'yellow wood', is highly valued for ship building,

but it is also used for poles, paneling, furniture, boxes, veneer and plywood.

The ripe seed is edible, but resinous. The bark and seeds are used in traditional

medicine. Bark decoctions or infusions are used as anodyne, also applied to itching

rash. Pulverized seeds are applied to treat tuberculosis, meningitis and sunburn. In

Ethiopia the seed oil is used in the treatment of gonorrhea. Afrocarpus falcatus is planted

as ornamental and roadside tree; sometimes it is also used as container plant and

Christmas tree. It is very useful for soil protection against water erosion. It is also

planted as wind break.

As well as S. birrea (marula), P. falcatus wood is creating wealth for people in different

furniture modes and exporting the wood itself, but as food it is under exploited. Even

though these two species, S. birrea and P. falcatus have all the above mentioned benefits

and known in different names for Sclerocarya birrea, (Amhara-Gomales (Yebrehalomi),

Oromo-didissa, Tigrigna-Abengul and Mursi-cobwe) (Muok BO, Khumalo SG, Tadesse

W. and Alem Sh. 2011), and Podocarpus falcatus (Amh. Zigba), processing of this

invaluable plant seed to oil and other edible products is not known in Ethiopia.

Therefore, designing of different options for development, production, improvement,

value addition and promotion of high value Non-Timber Forest Products are the most

important as it is easily generate income for the household and the nation while

improving environmental wellbeing.

Thus the overall goal of this project document underlines the aforementioned problems

through providing and generating technologies/information that could be utilized for

the multi-dimensional development of this invaluable fruit bearing trees.

5

Objectives of the study

General objective

The general objective of this study was to extract sclerocarya birrea (marula) and

podocarpus falcatus oils, study extraction conditions and to characterize optimum

condition extracted oils.

Specific objectives

The specific objectives of this study:

Determination of the effects of particle size, extraction time and moisture content

on oil yield.

To assess proximate composition of the optimally extracted oil

To determine the fatty acid profile of optimally extracted oil

Significance of the study

This thesis work generally resulted in:

Introduced edible oil production from highly underutilized Sclerocarya birrea

kernel and Podocarpus falcatus seed

Diversified income generation mechanism in the rural areas through collecting,

processing and cultivation of these oil bearing tree species.

Improved environmental wellbeing of the dry land area by easily generating

incomes.

Introduced different options for development, production, improvement, value

addition and promotion of high value Non-Timber Forest Products.

6

CHAPTER TWO

LITERATURE REVIEW

2.1 Oil and fat structure

Plant seed oils have a wide variety of structures, because oils do not occur in nature as

single pure entities, but rather as complex mixtures of molecular species in which

various fatty acids (FAs) and glycerin are present in different combinations (Christie,

1989). There are many different kinds of fats, but each is a variation on the same

chemical composition. Triglycerides are the main constituents of vegetable oils. All fats

consist of FAs (chains of carbon and hydrogen atoms, with a carboxylic acid group at

one end) bonded to a backbone structure, often glycerol (a "backbone" of carbon,

hydrogen, and oxygen) (Zamora, 2005). Chemically, this is a tri-ester of glycerol, an

ester being the molecule formed from the reaction of the carboxylic acid and an organic

alcohol (Gunstone and Herslof, 2000). Oils are usually from plants while fats are from

animal origin (O'Brien, 1998).

2.2 Importance of oils

Many plant oils are used in food, in medicine, cosmetics and as fuels. They are

consumed directly, or are used as ingredients in the preparation of food (O'Brien, 1998).

Fat and oil are the most concentrated kind of energy that humans can use (Odoemelam,

2005). They provide 9 kilocalories per gram of oil (Gurr, 1999) while the other two types

of energy that humans can use i.e. carbohydrates and proteins provide 4 kilocalories per

gram each (Lawson, 1995). The Food and Agriculture Organization (FAO, 2007) and the

World Health Organisation (WHO) have listed the important functions of dietary oils as

a source of energy, cell structure and membrane functions, source of essential FAs,

vehicle for oil-soluble vitamins and for control of blood lipids (Alvarez and Rodriguez,

2000).

Yaniv et.al. (1999) made an assay of Citrullus colocynthis utilized for oil production,

especially in Nigeria. Its oil contains a large amount of linoleic acid (C18:2) which is

7

important for human nutrition (Yaniv et.al. 1996). Such oil composition resembles

safflower oil and is very beneficial in human diets (Pioch and Vaitilingom, 2005). For

treating some conditions, such as rheumatoid arthritis or diabetic neuropathy, one may

try oils high in gamma linolenic acid, such as primrose oil. Here the oil is used as a

medication to treat symptoms of a disease with both positive and negative effects

(Athar and Nasir, 2005). Consuming oils high in polyunsaturated FAs can lower blood

cholesterol levels and thereby decrease the risk of cardiovascular diseases (Dagne and

Jonsson, 1997). Some oils have medicinal properties (Aubourg et al., 1993) while others

can make excellent excipients in pharmaceutical and cosmetical preparations (Alvarez

and Rodriguez, 2000).

Although many plant oils have good nutritional values, it is not yet clear whether they

can be safely consumed because toxicity has been associated with some oils. Even the

most common commercial plant oils, such as canola (rapeseed), soybeans, cottonseed or

castor oils in their crude form are not fit for human consumption without further

processing (C'molik and Pokorny', 2000). These processes include filtration,

neutralization and physical refining, fractionation, bleaching and deodorizing. Refining

removes undesirable impurities of oil whereas fractionation separates oils and fats on a

commercial scale into two or more groups (Gurr, 1999). Fractionation increases oils

range of use, shelf life and adds value (Ferris et al., 2001). The deodorizing makes

possible the production of neutral flavor food product i.e. tasteless and odorless oil

(Gunstone and Herslof, 2000) while the colorless oil production is the obvious result of

bleaching (Lawson, 1995).

Plant oils are used to make soaps, skin products, candles, perfumes and other cosmetic

products (Dawodu, 2009; Ferris et al., 2001). High unsaturated oils are suitable as drying

agents, and are used in making paints and other wood treatment products (Giuffre,

1996). They are also increasingly being used in the electrical industry as insulators since

they are non-toxic to the environment, biodegradable if spilled and have high flash and

fire points (Oommen et al., 1999).

8

Many plant oils have similar fuel properties to those of diesel fuel and may substitute

for this fuel, most significantly as engine fuel or for home heating oil (Schwab et al.,

1987). Crop plant oils already used as biofuels include canola, sunflower, soybean and

palm oils (Athar and Nasir, 2005). They can be used in pure form in methyl ester form

but they are often blended with regular diesel (Pioch and Vaitilingom, 2005).

2.3 Physicochemical characteristics of plant oil and Fatty Acid composition

To evaluate the suitability of plant oils for a given purpose, it is necessary to determine

their physicochemical characteristics and fatty acid composition (Bettis et al., 1982).

Plant oils vary in their physicochemical properties. These include specific gravity,

viscosity, saponification value, acidity and fatty acid composition.

2.3.1 Specific gravity

The specific gravity (SG) indicates the FAs average molecular weight of oil (Gunstone

and Herslof, 2000). It is the heaviness of a substance compared to that of water, and it is

expressed without units (Eren, 2000). The SG of plant oils is usually about 0.920 at 25°C

(Elert, 2000). The SG is proportional to the FAs mean chain-length of the oil, as the FA

chain-length is proportional to the FA molecular mass. As the temperature increases,

the SG of the oil decreases (Lawson, 1995). The common edible oils have SG from 0.88 to

0.94 (Toolbox, 2005) while oils used for fuel range from 0.82 to 1.08 (CSG, 2008).

2.3.2 Moisture Content

Moisture content is the measure of water in a material. According to the Food Standards

Committee (1979), the moisture content in foods is of great importance for many

scientific, technical and economic reasons. Moisture determination is important in many

industrial applications, for example, in the evaluation of material balance or processing

losses. It is important to know the optimum moisture content when processing foods.

The moisture content of food gives an indication of its shelf life and nutritive value, low

moisture content is a requirement for long storage life. Compounds that volatilize

9

under the same physical conditions as water also would be included; however, these

are usually negligible (Aurand et al., 1987).

2.3.3 Saponification value

Saponification value (SV) is defined as the number of milligrams of potassium

hydroxide required to saponify 1gram of oil (AOCS, 1993). It is an indicator of

molecular weight or size as a function of the chain lengths of the constituent FAs

(Agatemor, 2006). The saponification value of around 195 indicates that oil contains

mainly FAs of high molecular mass. For example, the saponification value of palm oil

ranges from 196 to 205, that of olive oil from 185 to 196, linseed oil from 193 to 195,

cotton seed from 193 to 195 and that of soy oil is around 193 (Pearson, 1981). One the

other hand oils having high saponification value (around 300) have mainly FAs of low

molecular mass and are useful for soapmaking (Alabi, 1993).

2.3.4 Oil acidity

The acidity of oil is given by the quantity of FAs derived from the hydrolysis of the

triglycerides i.e. separation of FA from the glycerol in the triglyceride (Gurr, 1999). This

alteration occurs under unsuitable conditions of treatment and preservation of the oil.

The oil acidity, can therefore, indicates the purity of the oil (Pérez-Camino et al., 2000).

The oil acidity is expressed either as the percentage of free FAs or in terms of the

number of milligrams of KOH required to neutralize one gram of sample (mg KOH/g)

(Gunstone and Herslof, 2000). Numerically the acidity of ordinary fats and oils is

approximately twice the percentage of free FAs (Dawodu, 2009).

Most unrefined oils contain high levels of acidity (Pioch and Vaitilingom, 2005), e.g.

soybean oil when unrefined or in crude form has an acidity level ranging between 1.2

and 2.8 mg KOH/g (Orthoefer and List, 2007) and crude palm oil between 6 and 12 mg

KOH/g (Egbe et al., 2000). Oils required for use in food have an acidity level less than

0.1 mg KOH/g (FAO, 1993) whereas a high acidity is preferred in biofuels (Pioch and

10

Vaitilingom, 2005). The oil content and physicochemical characteristics of oils for some

common plant crops are shown in Table 2.1.

Table 2.1 Oil content and characteristics of oils from some crops plants

Oil source Oil % MP (0C) SV Uns. % Oil acidity Reference

Canola 30 -9 168-181 0.2-2.0 - Rossel, 1987

Cocoa - 33 188-198 0.1-1.2 - Rossel, 1987

Coconut 35.3 24 248-265 0-0.5 - Rossel, 1987 Corn 4.0 -11 187-193 0.5-2.8 - Rossel, 1987

Cotton 36 0 193-195 0.2-1.5 - Rossel, 1987 Grape - -10 188-194 - - Rossel, 1987

Olive ? -1 185-196 0.7-1.5 - Rossel, 1987

Palm - 37 196-205 0.3-1.2 6 -12 Egbe et al., 2000; Pearson,

1981 Palm kernel 40 25 230-254 0.2-0.8 - Rossel, 1987 Peanut 49 - - - - Rossel, 1987

Safflower 59 -15 186-198 0.3-1.3 - Rossel, 1987 Sesame 49 - 2 187-195 0.9-2 - Rossel, 1987

Soybean 17.7 - 21 188-195 0.5-1.6 1.2- 2.8 Orthoefer and List, 2007;

Rossel, 1987 Sunflower 44 -17 188-194 0.3-1.3 - Rossel, 1987

2.3.5 Fatty acids

Fatty acids (FA) s are composed of carbon, hydrogen and oxygen arranged in a carbon

chain skeleton with a carboxyl group (-COOH) at the alpha position. FAs in biological

systems usually contain an even number of carbon atoms, typically between 8 and 24.

The FAs with 16- and 18-carbons are more frequent (GCRL, 2008). Fatty acids differ

from each other by the number of carbon atoms and the number degree and position of

unsaturation. There are three classes of FAs: Saturated FA (SFA), monounsaturated FA

(MUFA) and polyunsaturated FA (PUFA) (Christie, 1989). SFAs have carbon atoms

containing all the hydrogen atoms that they can hold. MUFAs have carbon chain

containing one double bond. PUFAs contain two or more double bonds.

There are two families of polyunsaturated FAs, the omega-3 and the omega-6 family

(NCPA, 2006). FAs have many physiological roles (Gurr, 1999). Essential FAs (EFA) are

those polyunsaturated FAs that are required in the human diet for growth and proper

11

functioning of the body (Erasmus, 1993). They include omega-3 FA such as α-linolenic

acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (Wijendran

and Hayes, 2004). Long-chain FAs (LCFA) are FAs having 20 or more carbons in their

chains as the case of arachidonic (20:4n6) and docosapentaenoic (22:5n3) acids

(Simopoulos, 1998).

2.3.5.1 Fatty acid nomenclature

In chemical nomenclature the carbon of the carboxyl group is carbon number one.

Greek numeric prefixes such as di, tri, tetra, penta, hexa, etc., are used indicator of the

length of carbon chains. Thus, "9, 12-octadecadienoic acid" indicates that this is an 18-

carbon chain (octa-deca) with two double bonds (di-en) located at carbons 9 and 12,

with carbon 1 constituting a carboxyl group (oic acid) (Zamora, 2005). FAs are

frequently represented by a notation such as 18:2 that indicates that the FA consists of

an 18-carbon chain and 2 double bonds (Beare-Rogers et al., 2001; Moss, 1976).

In biochemical nomenclature the terminal carbon atom is called the omega (ω) carbon

atom. The term "omega-3 or omega-6" signifies that their double bond occurs at carbon

number 3 or 6, respectively counted from and including the omega carbon. This makes

it possible to classify PUFA in families: Omega-3 and Omega-6. For example the acid

eicosapentaenoic 20:5 ω-3 (omega-3) has 20 carbon atoms and 5 unsaturations (20: 5)

and the first non-saturation is on carbon 17 (20 - 3 = 17). Also the arachidonic acid

(omega-6) is called “acid 20: 4 ω-6”, where the first double bond is at C14 carbon (20-

6=14). The “ω” can be replaced by a “∆” or “n” (GCRL, 2008). The names and

descriptions of some FAs found in biological materials are presented in Table 2.2.

12

Table 2.2 Names and descriptions of some fatty acids found in biological materials

Common name Scientific name

No. of double

bonds

Carbons Nr & Scientific

symbol

Reference

Lauric acid Dodecanoic acid 0 12:0 Beare-Rogers et al.,2001

Myristic acid Tetradecanoic acid 0 14:0 Christie, 1989

Palmitic acid Hexadecanoic acid 0 16:0 Beare-Rogers et al.,2001

Palmitoleic acid 9-Hexadecenoic acid 1 16:1n-7 Beare-Rogers et al.,2001

Stearic acid Octadecanoic acid 0 18:0 Beare-Rogers et al.,2001

Vaccenic Acid 11-Octadecenoic Acid 1 18:1 n-7 Christie, 1989

Oleic acid 9-Octadecenoic acid 1 18:1n-9 Christie, 1989

Linoleic acid 9,12-Octadecadienoic acid 2 18:2n-6 Christie, 1989

α-linolenic acid 9,12,15-Octadecatrienoic acid 3 18:3n-3 Christie, 1989

Arachidic acid Eicosanoic acid 0 20:0 Zamora, 2005

Gadoleic Acid 11-eicosenoic acid 1 20:1n-9 Zamora, 2005

EicosadienoicAcid 11,14-Ecosadienoic Acid 2 20:2 n-6 Christie, 1989

Eicosatrienoic Acid

11,14,17- Eicosatrienoic Acid 3 20:3 n-3 Christie, 1989

Arachidonic acid AA

8,11,14,17-Eicosatetraenoic acid 4 20:4n-3 Zamora, 2005

Arachidonic acid AA

5,8,11,14-Eicosatetraenoic acid 4 20:4n-6 Christie, 1989

EPA 5,8,11,14,17-Eicosapentaenoic acid

5 20:5n-3 Christie, 1989

Behenic acid docosanoic acid 0 22:0 Zamora, 2005

Erucic Acid 13-Docosenoic Acid 1 22:1 n-9 Christie, 1989

DHA 4,7,10,13,16,19-Docosahexaenoic acid

6 22:6n-3 Christie, 1989

Lignoceric acid Tetracosanoic acid 0 C24:0 Zamora, 2005

Nervonic Acid 15-Tetracosaenoic Acid 1 24:1 n-9 Christie, 1989

13

2.3.5.2 Fatty acid composition of plant oils

Plant oils characteristics are related to their fatty acid (FA) composition (Allena et al,

2004). The FA composition depends on the sources of the oils. The FA composition of

plant oils vary, depending on factors such as location of plants, growth area, soil

conditions and climate (Lawson, 1995). FA compositions of some commonly used edible

plant oils have oleic acid ranging from 40 to about 70%, linoleic acid from 22 to about

50% and linolenic acid from 1 to 10% (Lawson, 1995). The FAs compositions of some

common oils from some crop plants are presented in Table 2.3.

14

Table 2.3 Fatty acid composition of some crop plants

Crops name ω6/ω3 C8-C14 Palmitic Stearic Oleic Linoleic ALA Arachidic Reference

Canola Oil 4 - - 7.0 54.0 30.0 7.0 - Erasmus, 1993

Cocoa Butter - - 25.1 36.4 34.1 2.8 0.2 36.4 Dubois et al., 2007

Coconut oil - - 91.0 - 6.0 3.0 - - Erasmus, 1993

Corn Oil - - - 17.0 24.0 59.0 - - Erasmus, 1993

Cottonseed oil - - - 25 21 50 - - Erasmus, 1993

Grape seed oil - - - 12.0 17.0 71.0 - - Erasmus, 1993

Olive oil - - 12.1 2.6 72.50 9.40 0.6 0.4 Dubois et al., 2007

Palm oil - 1.7 43.8 4.4 39.1 10.2 0.3 0.3 Dubois et al., 2007

Palm olein - 1.00 37.00 4.00 46.00 11.00 - - Dubois et al., 2007;

Palm kernel oil - 71.6 8.4 1.6 16.4 3.1 - - Dubois et.al. 2007

Peanut oil - 0.1 10.4 3.00 48.00 30.30 0.4 1.2 Dubois et.al. 2007

Safflower oil - - - 12 13.0 75.00 - - Erasmus, 1993

Sesame oil - - - 13 42 45.00 - - Erasmus, 1993

Soybean oil 7 - 9.0 6.0 26.0 50.0 7.0 - Erasmus, 1993

Sunflower oil - - 6.4 4.5 22.1 65.6 0.5 0.3 Dubois et al., 2007; Zulberti, 1988

Aleurites

moluccana - - - - 18.80 46.86 25.43 - Giuffre et al., 1996

15

2.4 Sclerocarya birrea (Marula)

2.4.1 The Marula tree and its fruit

Sclerocarya birrea is commonly known as marula in southern Africa but other names are

used in other countries as well (Mutshinyalo & Tshisevhe, 2003). The genus Sclerocarya

comprises only 2 species; birrea and gillettii, but Shackleton et.al. (2001) noted that there

are actually four species with birrea having 3 subsp., namely Birrea, Caffra and

Multifoliolata. Sclerocarya birrea occurs naturally or cultivated in the Sahel, East and

Southern Africa outside the humid forest zone (Orwa, Mutua, Kindt, Jamnadass &

Simons, 2009). The tree prefers a warm and frost-free climate and is highly salt tolerant

(worldagroforestry.org, du Plessis, 2002). The Sclerocarya birrea tree can reach heights of

up to 18 m and a trunk diameter of 120 cm (Orwa et al., 2009 & von Teichman, 1982). The

tree (Figure 2.1) has a grey bark, short taproot of 2.4 m and lateral roots that can reach up

to 30 m (Orwa et al., 2009). The tree prefers clay soils or sandy loam soils and is common

in areas receiving 200-1370 mm of rainfall annually. It is a protected species and often

planted in crop fields by some farmers in Namibia and Botswana (Shackleton et al., 2001).

The fruits of marula abscise before ripening when they are still green and the time of fruit

abscission varies among trees (Nerd et al., 1994 and Bille &Steippich, 2003). After

abscission, the colour changes to yellow (Figure 2.1-2.3), aroma develops and the flesh

softens.

Figure 2.1 (A) Marula tree and (B) Marula tree bark.

A B

.

16

This happens 7-10 days after abscission (Nerd et al., 1990). The fruits (Figure 2.2) are

round and oval drupe and 3-5 cm in diameter when mature and develop in clusters of

three to five at the ends of twigs on a new growth (Mojeremane & Tshwenyane, 2004 and

Nerd et al., 1994). They have anepiderm that covers the flesh or pulp and a stone inside,

which is about 2-3 cm long with one to four cavities containing the seed (figure 3)

(Mojeremane & Tshwenyane, 2004). The edible part of the fruit is verysmall compared to

the fruit size; the average weight of the fruit is 18 g and the peel or skin, stone and flesh

make up 41%, 53% and 6% of total weight respectively (von Teichman, 1983).

2.4.2 The use of marula

Marula (Sclerocarya birrea subsp. Caffra) is one of the most important fruits and potential

sources of income for primary producers in the North and Central Regions of Okavango

and Caprivi in Namibia (du Plessis, 2002). It is also one of the most commonly utilized

indigenous wild fruit in Africa (Shackleton et al., 2001). The tree is highly appreciated by

rural communities for its fruits. Female trees bear plum-sized fruits with a thick yellow

peel and a translucent, white and highly aromatic sweet-sour fruit which is eaten raw like

a small mango, or used to prepare juices (Figure 2.2), jams, conserves, dry fruit rolls, and

alcoholic beverages (Nerd & Mizrahi, 1993 and Mizrahi & Nerd, 1996). The taste of the

fruit is said to be acidic and bitter but of pleasant flavour when fully ripe (Ogbobe, 1992).

Since its fruit kernels (Figure 2.3) are eaten or used for oil extraction, the marula is

considered a multipurpose tree (Mutshinyalo & Tshisevhe, 2003). The oil can be used for

cooking or for cosmetic purposes (du Plessis, 2002; Mojeremane & Tshwenyane, 2004).

17

Marula kernels are regarded as delicacy in regions of the tree’s natural habitat and are

commonly used to supplement the diet during winter season (Shone, 1979). They also

make good snacks and can be consumed raw or roasted for the purpose of adding a

unique flavour to the food. The nuts can be mixed with vegetables or meat or may be

ground by pounding and formed into a cake before consumption. In some households,

the ground nuts are used in baking traditional breads (Shone, 1979).

The wood from marula trees is used for making utensils, fencing poles as well as fuel

wood. For medicinal purposes, leaves, bark and roots are used. The leaves mainly used

for coughs while the bark and roots are for stomach-related ailments and other ailments,

notably fever,diarrhea and blood circulation problems. Mixed with other medicinal

plants, the bark is used by traditional healers to treat various illnesses such as syphilis,

leprosy, dysentery, hepatitis, rheumatism, gonorrhea, diabetes, dysentery and malaria,

particularly bark that is gathered before the first flush of the leaves (Mutshinyalo &

Tshisevhe, 2003).

Figure 2.2 Marula fruits (A) and squeezing marula juice (B)

Figure 2.3 Marula stone cracked (A) and extracting its kernel (B)

18

Other uses derived from marula tree include caterpillars that are edible, fodder for

livestock, nuts for rattles, beads and necklaces, hair relaxers as well as diviners die. At a

small scale, the epidermis of marula fruits can be dried in order to be used as a substitute

for coffee. Also at this scale the leaves are cooked as relish (Shackleton, Shackleton,

Cunningham, Lombard, Sullivan & Netshiluvhi, 2002).

Like many traditional food plants, tree species provides food at all times, including times

of food scarcity. In periods of the year characterized by shortages of crop harvest during

drought the first harvest Sclerocarya birrea can become a crucial source of nutrition

(Mojeremane & Tshwenyane, 2004). Even for livestock during drought, branches of

Sclerocarya birrea are cut by livestock owners to get the leaves as fodder for their animals

(Mojeremane & Tshwenyane, 2004).

Figure 2.4 Mini marula festival

2.4.2.1 Marula as a food

Ripe marula fruit can be consumed by biting or cutting through the thick, leathery skin

and sucking the juice or chewing the mucilaginous flesh after removal of the skin (von

Teichman, 1982). A popular fermented alcoholic beverage is prepared from the ripe fruit.

In some cases the skin is removed and the juice is fermented together with the pulp still

on the seed. Other methods include the cutting of the skin and allowing the whole fruit to

ferment (Carr, 1957). The traditional way of fermenting the fruits in beverage preparation

commonly known as ‘marula-beer’ or “marula-wine” (Shone, 1979) with an alcohol

content of 2-5% (Dlamini and Dube, 2008) and is used for the famous South African

“Amarula Cream Liqueur”.

1

19

Marula kernels found inside the nut of the fruit are regarded as a delicacy in regions of

the tree’s natural inhabitant; they are commonly used to supplement the diet during

winter (Shone, 1979), they make good snacks and can be consumed raw or roasted to add

a unique flavour to the food. The nuts are mixed with vegetables or meat or may be

grounded by pounding and formed into a cake before serving. In some households, the

grounded nuts are used in baking of traditional breads (Shone, 1979). Oil for human

consumption and for cosmetic purposes can also be extracted from the nuts (Pierre, 2002).

More recently, the fruit has been used in jelly or jam preparation, which is sold on a

small-scale (Bille and Steppich, 2003). The taste of marula jam and jelly is reported to be

good, and the colour is attractive (waxy yellow) without the need for addition of artificial

food colors. The epidermis of marula fruits can be dried in order to use it as substitute for

coffee. The leaves are cooked as relish. During droughts, branches of Sclerocarya birrea are

harvested by livestock owners to use leaves as fodder for livestock (Mojeremane and

Tshwenyane, 2004).

Like many traditional food plants, the tree species provide food at all times and

community use it during food shortage. In times of subsistence shortages, such as a

season of hunger preceding the first harvest, or in times of famine and drought, S. birrea

can become a crucial source of nutrition (Mojeremane and Tshwenyane, 2004).

2.4.3 Nutritional Status

2.4.3.1 Flesh

The flesh has a high moisture content of 83-91.7%. It has an especially high vitamin C

content, up to 400 mg/100 g fresh matter (Eromosele et al., 1991; Jaenicke & Thiong’o,

2000), which is several times higher than that of citrus. This makes the fruits an important

nutritional component in the local diet (Table 2.4). Poor people also consume the fresh

fruits to prevent common colds (Arnold et al., 1985; Erkkila & Siskonen, 1992). The

Carbohydrate levels range between 7% and 16%, where mainly consisted of sucrosewith

smaller quantities of glucose and fructose(Taylor & Kwerepe, 1995; Jaenicke & Thiong’o,

20

2000). Excluding ascorbic acid, citric acid is the most abundant of the organic acids

(Weinert et al., 1990).

2.4.3.2 Kernel

2.4.3.2.1 Proximate fractions, vitamins and mineral content

The kernels have a low moisture content, and high fat, protein and mineral contents

(Table 2.4). They are highly nutritious with 27-32% protein, 2.02%citric acid, malic acid,

sugar, phosphorus, magnesium, copper, zinc, thiamine and nicotinic acid. Protein levels

of 54-70%have been reported for de-fatted nuts (Burger et al., 1987).

2.4.3.2.2 Amino acids

The essential amino acid content of the marula nut (Table 2.5), with the exception of

lysine, which is deficient, has been compared to human milk and whole hen’s eggs

(Weinert et al., 1990). Due to the small amounts of lysine (in comparison to other nuts),

the marula nut would not be suitable to supplement cereal diets which normally lack

lysine. Levels of alanine, aspartic acid, leucine, phenylalanine, praline and tyrosine are

low but it is rich in glutamic acid, at about 24 g/100 g protein, and arginine (Busson, 1965;

Burger et al., 1987).

2.4.3.3 Kernel oil

2.4.3.3.1 Physicochemical characteristics

Marula oil has been successfully refined at both bench and commercial scales. The

extracted unrefined oil has a clear, light yellow colour and is suitable for soap

manufacture and edible use (Shone, 1979; Ogbobe, 1992). The specific gravity and the

saponification value (Table 2.6) are comparable to those of olive oil. The iodine value is

also near to that of olive oil but is, nevertheless, relatively low compared to sunflower oil

(Weinert et al., 1990). The oxidative stability of marula oil is thought to explain its

potential utilization in traditional meat preservation processes (Shackleton et al.,

2002).However, as a source of vitamin E, the oil is of poor quality, containing only some

23mg/100 g of tocopherols, little of this being α-tocopherol (Burger et al., 1987).

21

Table 2.4 Nutritional composition of pulp and kernel

Pla

nt

par

t

En

erg

y (

kJ/

100

wei

gh

t)

Wat

er (

%)

Pro

tein

(%

)

Fib

er (

%)

Fat

(%

)

To

tal

CH

O (

%)

Ash

(%

)

Vit

C (

mg

/100

g f

lesh

)

Th

iam

in (

mg

/100

g)

Rib

ofl

avin

(m

g/1

00g

)

Nia

cin

/Nic

oti

nic

(m

g/1

00g

)

Ca

(mg

/100

g)

Co

(m

g/1

00 g

)

Cu

(m

g/1

00 g

)

Fe

(mg

/100

g)

K (

mg

/100

g)

Mg

(m

g/1

00 g

)

Mn

(m

g/1

00 g

)

Na

(mg

/100

g)

P (

mg

/100

g)

Si

(mg

/100

g)

Zn

(m

g/1

00 g

)

Ref

eren

ce

flesh 225* 85 3.3 8 2.7 80 6 194 0.03 0.02 0.27 20.1 0.07 0.5 317 25.3 2.24 11.5 0.1 caffra Arnold etai. (1985): Botswana/Namibia

kernel 2703 4 29.5 3 59.7 3.9 4 - 0.42 0.12 0.72 118 2.81 4.87 601 462 3.81 808 5.19 caffra Arnold etai. (1985): Botswana/Namibia

kernel - 3.7 30.6 3.8 61.5 1.3 6.1 - - - - 170 - - - - - 1040 - birrea Busson (1986): Cote d'Ivoire

flesh - 86-87 - - - - - 53-179 - - - - - - - - - - - caffra Carr (1957): Zimbabwe

flesh - - - - - - - 403 - - - 36.2 0.13 0.1 1.12 - 31.9 0.11 - 18 0.34 birrea Eromosele etai. (1991): Nigeria

kernel - 3.9 28.7 4.7 58.5 3.9 4.3 - - - - 161 - - - - - - - 1907 - caffra Ferrao & Xabregas (1960): Angola

flesh - - - - - - - - - - - 481 - - 2.49 - 310 - 15.2 264 - birrea Glew et.al. (1997): Burkina Faso

kernel - - - - - - - - - - - 156 - - 2.78 - 193 - 11.9 212 2.65 birrea Glew etai. (1997): Burkina Faso

flesh 6.9 9.2 6.6 68.5 8.8 800 - 2700 400 200 400 birrea Houérou (1980): Senegal

kernel - 4.6 30.4 - 57 - - - - - - 150 - 1.97 5.23 555 355 0.5 - 761 - 5.72 Jaenicke & Thiong’o (2000): Kenya

flesh 1461* 83 4.2 9.1 10.1 70 6.6 - - - - 250 - - 40 - - - - 225 - - caffra Malaisse & Parent (1985): Democratic

Republic of Congo

flesh - - - - - - - 68 - - - - - - - - - - - - - - caffra Maghembe et.al. (1994): Zambia

kernel - - 23-31 - 56-61 - - - - - - - - - - - - - - - - - caffra Maghembe et.al. (1994): Zambia

kernel 2447 0 31.2 4 53.1 8.2 3.5 - - - - 80 - - 60 - - - - 1600 - - caffra Malaisse & Parent (1985): Democratic Republic of Congo

kernel 2700 3.9 27 3.6 58.9 5.9 3.6 - 0.43 0.12 0.72 130 3.6 - 9.3 525 457 - 4.2 779 - 4.9 caffra National Food Research Institute (1972): South Africa

kernel 9 30.3 3.1 59.7 5.8 4.1 0.2 0.74 93 8.1 4.4 675 329 81 774 - 2.9 caffra Oliveira (1974): Mozambique

22

Table 2.5 Amino acid composition of S.birrea kernel meal, kernels and, fruit flesh

(g/100 g protein)

Amino acid

Kernel meal

(Southern Africa)

Burgeret.al. (1987)*

Kernel

(Angola)

Ferrao &

Xabregas

(1960)

Kernel

(Mozambique)

Oliveira

(1974)

Kernel

(Ivory

Coast)

Busson

(1965)

Kernel

(Burkina

Faso)

Glew et.al.

(1997)

Fruit flesh

(Burkina

Faso)

Glew et.al.

(1997)

Alanine 2.7±0.38 3.2

Arginine 14.2±2.03 14.15 15.8

Aspartic acid 6.4±0.75 7.9

Cystine 2.30 3.48 2.69

Cystine (half) 1.6±0.34

Glutamic acid 23.2±3.46 25.8

Glycine 4.2±0.57 5.0

Histidine 2.5±0.23 2.28 2.4

Isoleucine 3.2±0.37 5.47 5.03 4.0 4.52 5.08

Leucine 5.0±0.54 4.74 5.58 5.9 6.75 7.61

Lysine 1.6±0.09 1.81 2.43 1.9 2.30 4.36

Methionine 1.5±0.26 2.28 1.89 1.6 1.21 1.42

Phenylalanine 3.5±0.37 3.37 4.72 4.8 4.23 4.44

Proline 2.1±0.35 3.3

Serine 3.8±0.38 4.4

Threonine 1.8±0.19 1.38 2.09 2.3

Tryptophan 2.64 1.31 1.48 1.44

Tyrosine 2.6±0.30 2.30 3.5 2.63 3.67

Valine 3.9±0.43 12.42 6.52 4.8 5.41 6.03

*, mean ± standard deviation

Table 2.6 Physicochemical characteristics of Sclerocaryabirrea kernel oil

Assay Shone (1979) South Africa

Ligthelm et.al. (1951)

Southern Africa

Shackleton et.al. (2001)

Southern Africa

Weinert et.al. (1990) Sudan

Ogbobe (1992)

Nigeria

Melting point (°C) 25 26-28 Refractive index 1.46 1.46 1.46 1.46 Specific gravity 0.92 0.91 0.88 Acid value 3.7 14.8 1.3 33.7 Peroxide value 0 4.58 Saponification value 193.5 190.0 191 199.8 162.7 Hydroxyl value 2.6 Iodine value 76.6 74.4 70-80 65.7 100.25 Unsaponifiable 0.6 2.4 0.82 3.06 Sterols (mg/100 g) 900 410

23

2.4.3.3.2 Fatty acids

The oil content (53-61% of the kernel by weight) has (Table 2.7) a very good dietetic

ratio of saturated (palmitic and stearic) to unsaturated (linoleic and oleic) fatty acids

(Weinert et al., 1990; M.K. Thiong’o, pers. comm.). The fatty acid profile is similar to that

of olive oil, but with a stability that is ten times greater. It has a high mono-unsaturated

content of oleic acid (C 18:1 - 66-74%) suggesting a good oxidative stability. Its

exceptional stability has been attributed to its fatty acid composition (high oleic acid

content) as it has a relatively low total tocopherol content, an average of 22 mg to 27 mg

per 100 g oil, and low P-tocopherol in particular - 0.04-0.06 mg per 100 g oil (Burger et

al., 1987; Weinert et al., 1990). Recently, however, this explanation has been challenged

(Shackleton et al., 2001) and the action of some minor oil components suggested as an

alternative.

Table 2.7 Principal fatty acids of Sclerocarya birrea fruit flesh, kernel, kernel oil, and olive oil

Flesh Kernel Kernel oil

Olive oil Glew et.al. (1997)*

Glew et.al.

(1997)**

Busson (1965)

(g/100g fatty acid)

Ligthelm Shone (1979)

Burger et.al. (1987)

Thiong’o et.al. (unpublished)

C16:0 (palmitic)

43.0 19.7 17.4 16.1 1 2.0 11.2-15.3 12.7-14.7 9.4

C18:0 (stearic)

4.8 0.4 8.7 5.1 9.2 5.9-6.9 trace-3.0 2.8

C18:1 (oleic)

4.0 60.0 63.9 66.7 69.9 70.4-74.3 64.3-71.2 76.3

C18:2 (linoleic)

1 5.6 4.4 3.9 7.3 7.8 4.7-9.2 12.1-13.9 8.0

C18:3 (linolenic)

20.9 0.3 1.7 trace - 0.1 trace-0.2 0.6

*, total lipid content 13.5% dry weight; **, total lipid content 19.5% dry weight; -, no value

given

24

2.4.3.4 Beer from the fruit pulp

Investigation into the quality of traditional beer brewed in Swaziland, including marula

beer was undertaken by Shongwe (1996). He reported that the quality of marula beer

was comparable to that of some commercial beer. Marula beer was nutritious and not as

intoxicating as other beers (Table 2.8) but methanol, a poisonous alcohol, is found in

some locally brewed marula beer (Tiisekwa et al., 1996).

Table 2.8 Composition of marula beer

Parameter Values

pH 3.6

Total titrable acidity (g/100 g) 1.1

Fixed acidity (g/100 g) 0.1

Volatile acidity (g/100 g) 0.9

Total soluble solids (%) 9.0

Total solids (%) 7.6

Ash (%) 0.4

Alcohol content (% v/v) 5.8

Carbohydrate (%) 10.0

Crude protein (% per liter) 2.6

Presence of bacteria Formed

Source: Shongwe (1996)

Tiisekwa et.al. (1996), using experienced brewers, simulated traditional marula wine

production under “controlled” laboratory conditions. They found ethanol to be the

main fermentable product (Table 2.9). The ethanol concentration of 6% is lower than

that in commercial wine (11-12%), but comparable with ciders and slightly higher than

in beers (ca 4.4%). The concentration varies depending on the brewing technique.

Tiisekwa et.al.(1996) reported a slightly lower value (5.8% v/v alcohol) for one sample.

25

Table 2.9 Concentrations of mineral elements and fermentation products of home-made marula wine

Element/product Concentration

Methanol Below detection

Ethanol (% v/v) 6.0 ± 1

Ethyl acetate Below detection

N-propanol Below detection

Acetaldehyde Below detection

Cadmium Below detection Zinc (ppm) 27 ± 2

Manganese (ppm) 16 ± 2

Iron (ppm) 50 ± 3

Lead (ppm) 140 ± 10

2.4.4 Food items based on Pulp, Skin and Juice

2.4.4.1 Fresh fruit

All parts of the fruit are edible raw (Palmer & Pitman, 1972-1974; Shone, 1979;

Teichman, 1983), making it a potential ‘fresh produce’ item. Due to the plant restricted

area distribution, prospects for developing a ‘local’ market for ‘fresh’ marula are lower

than those for developing an urban or international market - within or outside Africa.

Given transport and storage considerations, the urban and tourist markets are the ones

most likely to develop.

2.4.4.2 Marula-based jam and jelly

Potential products based on the pulp, of nutritional value particularly on account of

reported vitamin C levels as high as 200 mg per 100 g fresh flesh (Arnold et al., 1991)

and 400 mg per 100 g fresh flesh (Eremosele et al., 1991), include sun-dried fruit, cooked

jams and preserves. It has long been recognized that richness in vitamin C is preserved

in suitably prepared jam and jelly (Carr, 1957). Attempts to commercialize marula jelly

production have been made in South Africa but have enjoyed mixed success

(Shackleton et al., 2001). The Parastatal organization, Lisbon Estates, operating in an

area rich in Sclerocarya birrea subsp. caffra close to the Kruger National Park, began to

26

produce and market marula jelly in 1983 but, as demand did not rise, ceased this

activity in 2001. In contrast, an initiative to market marula jam produced at household

level not far away, at Thulamahashe, was swamped with the demand and the producer

was unable to cope (S. Barton, pers. comm.). Another South African enterprise, Ina

Lessing Jams, still continues production of jam and jelly, having started marketing these

commodities within South Africa during the 1990s. To make jam, fruits are collected

after they have fallen from the tree but are still ‘green’ (before they have begun to

ferment). Fruits are incised with a cross and then boiled for 20 minutes in enough

amount of water to cover the fruits. The liquid “syrup” separated from the kernel where

the liquid and sugar are then recombined with pulp, at a ratio of 1cup of sugar to 3 cups

of liquid. This mixture is then boiled for 40 to 50 minutes, until it turns brown. It is then

bottled. Commercial prospects for jam production are being explored by Veld Products

Research and Development in Botswana, with superior supermarkets and tourists

viewed as potential customers

2.4.4.3 Confectionary

‘Marula chunks’ are a new confectionary item being made from the skin of ripe (‘soft-

skinned’) fruit. After fruit contents (pulp and stone) have been removed, the skin is

crushed or sliced up and sugar- coated. This is a product included in the current pilot

initiative of Veld Products Research and Development, in Botswana.

2.4.4.4 Juice, nectar, puree and flavoured products

The juice of the fruit, noteworthy for the high vitamin C content of around 200 mg per

100 g juice (Fox & Stone, 1938, Arnold et al., 1991), can be used directly as a refreshing

drink (Weinert et al., 1990; Leakey, 1999), or reduced to make a flavouring extract for ice

cream, yoghurt, soft drinks, cookies and cakes, and a marula-flavoured candy is

available - ‘Marula Cream Praline’ (Nestle; //www.safpp.co.za/marula/). A product

now being introduced into the urban marketplace is a marula-flavoured shortbread.

Almost 20 years ago it was estimated that some 600 t juice were processed annually in

South Africa and that demand appeared to be increasing (Weinert et al., 1990). Within a

27

few years, pasteurized juice was tested in Botswana as a market commodity (Taylor &

Kwerepe, 1995) but the initiative encountered problems of product stability and cost-

effectiveness and is now in abeyance (Shackleton et al., 2001). Despite promising

indications (Shackleton et al., 2001), production of a marula-based puree through the

same Botswana programme was also halted as insufficiently commercially rewarding.

Internationally, a vitamin-enhanced juice drink (15% juice) with rich mouth feel,

promoted as Sclerocarya (marula) flavoured (based on a supply from Mozambique), was

released in the United States market in 2000.

2.4.4.5 Alcoholic beverages

Liqueur and cider (usually termed ‘beer’) are today well established marula-based

alcoholic beverages, the latter with a traditional pedigree suspected to date back

hundreds of years (Palmer & Pitman, 1972-1974). The South African ‘Amarula’ cream

liqueur is internationally the most familiar marula product. Its production, by Cape

Distell, is the largest and longest-standing (20 years) commercial marula enterprise, and

currently the liqueur enjoys an expanding status in the global market (Shackleton et al.,

2001). According to Leakey (1999), trees from drier environments have sweeter fruits

than those from wetter areas and it is the sweeter fruitsthat are used for liqueur

production (Shackleton et al., 2000. However, Schafer & McGill (1986) link a sweeter

flavour with the lower rainfall of Namibia. A second enterprise in South Africa

independently produces another liqueur from marula on a limited scale and the

multinational Bulmer Cider Company has expressed interest in working with a South

African partner to do the same (S. Barton, pers. comm.). In Israel, too, liqueur is being

produced, reputedly with a higher content of marula material (Shackleton et al., 2001; S.

Barton, pers. comm.). Wine, under the name ‘Marulam’, has been produced and

marketed in Zambia (Leakey, 1999).

The importance of marula beer extends beyond a simple role as another alcoholic

beverage. Much ceremony associated with its consumption persists and is credited with

contributing to social cohesion and maintenance of societal standards. Nutritionally, it

28

is noteworthy for the high vitamin C content (50-140 mg per 100 g) that remains after

fermentation (Weinert et al., 1990). The distinctive and unique flavour of marula

ferment makes it desirable.

2.4.5 Items based on kernels

2.4.5.1 Extracted kernels

Attractive nutritional qualities which make the kernels of Sclerocarya birrea potentially

demanded for high energy, protein, fat, magnesium, phosphorus and potassium

contents. The endocarps (nuts) can be cracked, and the kernels (which taste like cashew

nuts) removed, to be eaten fresh and raw. They can be packaged at household level and

marketed by street vendors, as in West Africa (J.B. Hall, pers. comm. - subsp. birrea).

There is also (C. Shackleton, pers. comm.) a growing, if small, local rural market for

extracted kernels of subsp. caffra in South Africa. However, the shelf life of extracted

kernels is limited. There are instances (S. Barton, pers. comm.) of bacterial activity

making them unsuitable for consumption, possibly through carcinogenic qualities.

Rural communities counter this risk by consuming kernels soon after extraction.

Bacterial deterioration apparently does not occur while kernels remain within the

endocarp making this a safe, if bulky, storage option under household circumstances.

2.4.5.2 Oil

Marula oil has often been described as fairly similar to olive oil (e.g. Burger et al., 1987),

but with the positive feature of a more oxidatively stable fatty acid composition.

Another nutritionally attractive characteristic is the favorable saturated-to-unsaturated

fatty acid ratio. On the negative side, the free fatty acid content is associated with high

hydrolytic rancidity which must be countered with appropriate and specialized steps in

the refining process (S. Barton, pers. comm.). Exploratory attempts to extract and refine

oil from marula kernels within South Africa have been made but difficulties were

encountered at various stages in the process - acquisition of kernels, oil extraction, the

refinement process and selling (S. Barton, pers. comm.). However, a potential market

for marula oil is still perceived. Additional end products in which marula oil is a

29

component have been suggested or are being marketed. Burger et.al. (1987) note food

industry potential for coating dried fruit, as a frying oil and in baby foods. Use in

Zimbabwe in soap, and in South Africa as an aromatherapy carrier oil is taking place (S.

Barton, pers. comm.). The potential value of oil by-products as a sunscreen has attracted

interest (Roodt, 1988), and oil extracted from kernels in Madagascar, and processed in-

country, is sold as a moisturizer under the name ‘Sokoa’ oil.

2.5 Podocarpus falcatus

Podocarpus falcatus, which belongs to the family Podocarpaceae, grows at 1500-2500 m

altitude above sea level in areas with mean annual rainfall of 1200-1800 mm (Azene

2007). It is an evergreen tree reaching up to 46 m in height with long, cylindrical trunk.

This species is native to east and southern Africa, especially the Afromontane forest. It

is known in different names, East African yellowwood, outeninqua yellowwood (Eng.);

zigba (Ethiopia); mse mawe, olvirviri, owiriwiri (Tanzania); musenene, obwipe, omufu

(Uganda); outeniekwageelhout, umsonti (Africaans); umSonti (Zulu); podo (trade

name).

In Ethiopia, P. falcatus, locally known as “zigba”, is mainly found in Assela, Bale, east of

Lake Awasa, Jemjem and the Megada forests of Sidamo and Wollega (Getachew &

Demel 2005).

The attractive yellow or yellow-brown timber is popular for the manufacture of fine

furniture. It is of high quality with very fine grain, the density varying from 480 to 599

kg/m3 at 12-15% moisture content (WUARC 1995).

The timber is also used as standard building timber, for flooring and roofing and it is

suitable for firewood. The bark contains 3-6% tannin and is used for tanning leather, the

fruit is edible and oil from the seeds is used for medicinal purposes. The large, dense

crown makes it suitable for shade and windbreaks and the attractive shape has made it

popular as an ornamental tree in cities, it is locally the most preferred timber for butter

and cheese boxes and other food containers. Due to the intensive utilisation of its

30

timber, it is currently found in the highlands as scattered trees, restricted to farmlands

and patches around riverbanks. Apart from timber values, local communities of Assela,

Shashemene and Hirna collect the fruit of P. falcatus growing in their areas to produce

edible oil.

Podocarpus belongs to the gymnosperms so no fruit layer is produced, the seeds are

borne “naked” inside the cone. The fruit (which is actually the seed) of Podocarpus tree

is greenish-blue ovoid in shape, about 1-1.85 cm long and 1-1.25 cm in diameter. It turns

yellowish to purplish when ripe and contains a single seed in hard-shelled coat. In the

traditional way of oil extraction, sun-dried seed is crushed, heated in a pan and boiled

with water to produce approximately 10% oil (Demel 1994).

(A) (B)

Figure 2.5 P. falcatus (A) Fruit (B) Dried seed

31

CHAPTER THREE

MATERIALS AND METHODS

3.1 Materials

3.1.1 Study sample

Two basic raw materials were used in this research project, sclerocarya birrea fruit and

podocarpus falcatus seed:

Marula (Sclerocarya birrea) fruitwas collected, stored in cold ice box and transported

from Arbaminch, Nech Sar National Parkand Zigba (Podocarpus falcatus) seed was

obtained from Ethiopian Institute of Agricultural Research, Forestry Research Center

(FRC) which is located in Addis Ababa for the purpose of this research.

3.1.2 Equipment and Data Collection

Data were collected for the study and these included proximate composition data,

moisture and solvent; and physicochemical properties of the oil extract. Equipment

used for the study included a Soxhlet apparatus, desiccator, drying oven, weighing

scale, laboratory mill, laboratory equipment, chemicals and reagents, and computer

with appropriate software for data entry, organization and analysis.

3.2 Frame work of the experiment

The simplified overall framework of experiments of the thesis was shown in Figure 3.1.

32

Figure 3.1 Frame work of the experiment

Sclerocarya birrea Fruit Podocarpus falcatus seed

Juice Skin Nut

Proximate analysis

- Moisture content

- Crude fiber

- Ash

- Vitamin C

- Calcium (Ca)

- Potassium (K)

- Sodium (Na)

Kernel Shell

Size reduction

<0.2, 0.2-0.6 mm, 0.6-1.18 mm and 1.18-2.36 mm

Moisture content Adjustment

9 %, 12 % and 15 %

Solvent Extraction (n-Hexane

as a solvent)

2h, 3h and 4h

Optimal condition extracted oils

GC-MS Analysis

- Fatty Acid Profile

Physico-chemical analysis

- Acid value

- Peroxide value

- Specific gravity

- Refractive index

- Saponification value

- Free fatty acid

- Viscosity

Mineral content

Analysis

- Ash

- Calcium (Ca)

- Potassium (K)

- Sodium (Na)

33

3.3 Methods

3.3.1 Sample preparation

3.3.1.1 Marula (Sclerocarya birrea)

From collected marula fruits damaged and unripen fruits were manually sorted out and

the selected fruits were washed by tap water to remove dirt. The outer cover of the

collected marula fruit were peeled manually to separate the juice, nut and pulp (Figure

3.2). The juice was extracted by squeezing the fruit by hand prior to peeling and

proximate analyses were conducted. The nuts were slightly dried inorder to ease

crushing and separation of the kernels. Two methods were tested for crushing of the

nut, one is by using stone hammering (Figure 3.3 a) the second is a simplified metal

equipment which is cutter type (Figure 3.3 b). For conducting this research both

methods were developed and applied and the best method (metal cutter) were selected

as easy method of application.

(a) (b)

Figure 3.2 Marula (a) fruit (b) from left to right: juice, nut and pulp

(a) (b)

Figure 3.3 Methods for cracking marula nut (a) stone crushing (b) metal cutter

34

3.3.1.2 Podo (Podocarpus falcatus)

Crackedpodocarpus falcatus seed samples were sorted manually and prepared for size

reduction.

Figure 3.4 Sorted and cleaned podocarpus falcatus seed

3.3.1.3 Preliminary Works

Particle Size Determination

Cleaned and dried S. birrea (marula) and P. falcatus (podo) samples were milled using a

laboratory mill. The samples were sieved and categorized into fine (less than 0.6mm),

medium (0.6 - 1.18 mm), and coarse (1.18 - 2.36 mm). Sieved and categorized samples

were extracted by soxhlet using n-hexane as a solvent for three hours. This is used to

investigate the effect of particles size on oil yield and to fix the optimum particle size for

further extraction of the oils.

Figure 3.5 Ground and Sieved podocarpus falcatus seed

35

3.3.1.4 Moisture content adjustment

Moisture contents of the ground S. birrea kernel and P. falcatus seed was determined by

the method of the Association of Official Analytical Chemists‟ (AOAC, 2000); the

Official Method 925.10, by drying the samples in an oven at 105 oC until a constant

weight was obtained, The moisture content of the samples found to be 9 % and

8.42%respectively for marula and podo in wet basis. Knowing the initial moisture

content and the mass of marula and podo kernel in each jar the required mass of

distilled water was added to reach the target moisture content of 9, 12 and 15% in wet

basis (Zewdu et al., 2007).

� =����� − ���

�100 − ��� Eq. [3.1]

Where: Q is the mass of distilled water to be added in kg;

Wi is the initial mass of the sample in kg;

Mi is the initial moisture content of the sample in % w. b., and

Mf is the final moisture content in % w. b.

The required amount of distilled water were added to each glass jars, then kept in

drying oven at 600C for 4hr (Mpagalile et al., 2007) and in refrigerator at -16 0C for 2 days

to reach equilibrium in moisture content with the jar. The jars were shaken at regular

interval to facilitate internal moisture stabilization. After equilibration the samples were

checked for their moisture content.

3.3.2 Proximate Analysis

3.3.2.1 Moisture content determination

Moisture content was determined by the method of the Association of Official

Analytical Chemists‟ (AOAC, 2000); the Official Method 925.10, by drying the samples

in an oven at 105 0C until a constant weight was obtained. The crucible with its content

was put into air drying oven at 105°C for 5hr and placed in desiccators to cool. The

36

weight of the crucible (W1), sample with dry crucible, (W2) dried at 105ºC until constant

mass was attained and after cooling in desiccators to room temperature it was again

weighed (W3). The samples were then cooled in desiccators and weighed. The process

was repeated until a constant weight was obtained. The loss in weight expressed as a

percentage of the initial weight of sample gave the percent moisture content. The

moisture content was determined using equation (3.2).

�������� ������� (%) =�� − ��

�� − ��× 100 Eq. [3.2]

3.3.2.2 Solvent extraction

The following procedure was used in the extraction of samples. 30g of the milled

sample (for each triplicate) conditioned at moisture contents of 9%, 12% and 15%

were packed and used for the extraction process; using a Soxhlet apparatus. 150ml

of each solvent was measured into 250ml round bottom flask and heated at a

constant temperature of 70oC to reflux. The process of refluxing was continued for

the durations of 2, 3and 4 hours for each replicate. The residual hexane was

separated using a rotary vacuum evaporator (Model: Stuart, Stone, Staffordshire,

ST15 USA. The oil in the round bottom flask was placed on a water bath at 750C, and

finally dried in the oven for 30 minutes at 103o C.The yield was expressed by the

following formula: (Vanesa et al., 2011).

��� ����� (%) = ���� �� ��� ��������� (�)

���� �� ������ (�)× 100% Eq. [3.3]

3.3.2.3 Oil Content

Oil content: The oil content was gravimetrically determined and expressed as weight

percentage on dry basis (Vanesa et al., 2011).

��� ����� ��� (%) = ���� �� ��� ��������� (�)

���� �� ������ (�) ∗ �����. �� ������× 100% Eq. [3.4]

Where:

Coefficient of drying = 100 – moisture content of sample (%)

37

3.3.2.4 Specific Gravity (Relative Density)

Specific gravity for each of S. birrea and P. falcatus oils were measured according to

(AOAC, 920.212 (2000)) with a 25mL capacity Gay-Lussac bottle which was calibrated

with water. To calculate the specific gravity, the weights of (a) a completely dried Gay-

Lussac bottle, (b) the completely dried Gay-Lussac bottle with distilled water which

was heated to 400C in a water bath, and (c) the completely dried Gay-Lussac bottle with

oil heated to 400C in the water bath were measured.

The specific gravity will be calculated by using the following formula:

Specific gravity =Density �� ��� (� − �)

Density of Water (b − a) Eq. [3.5]

3.3.2.5 Acid value and Free fatty acid value

Acid value for each S. birrea and P. falcatus oil were measured according to (AOAC,

2000) 2.5 g of melted filtered oil sample was placed in a 250 mL Erlenmeyer flaskwhich

was filled with 150 mL of neutralized 1:1 (v:v) ethanol and diethyl ether solution. The

mixture was titrated with potassium hydroxide (0.1 N) ethanolic solution until the pink

color appeared and lasted for at least 10 seconds.Acid value and free fatty acid value are

calculated by the following formulas:

Acid Value =56.1 ∗ � ∗ �

W Eq. [3.6]

���� ����� �cid (%) =���� �����

1.99 Eq. [3.7]

Where:

T = Normality of standardized potassium hydroxide solution,

W= is the weight (g) of the test portion.

V= Volume of KOH ethanolic solution used for titration (mL).

38

3.3.2.6 Peroxide Value

Peroxide value for each S. birrea and P. falcatus oil was measured following AOAC,

965.33 (2000). About 5g (weighed to 0.001 g accuracy) of melted filtered oil sample was

placed in 250 mL capacity Erlenmeyer flask. Then 30 mL of acetic acid-chloroform

solution (3:2) and 1 mL of potassium iodide saturated solution was added, then let

stand for a minute in a dark. 2 mL of starch solution used as indicator and 30 mL of

distilled water were added. The resultant mixture showing dark purple to dark brown

was titrated with standardized 0.01 N sodium thiosulfate solutions until the color of the

mixture turned from ivory to white color.

Peroxide value (PV) was calculated by the following formula:

Peroxide Value �mEq

kg� = (V ∗ T)/W) ∗ 1000 Eq. [3.8]

Where: V = Volume in ml of standardized Na2S2O3 (blank was considered for

correction).

Where: T = Exact normality of the sodium thiosulfate solution used.

Where: W = Weight (g) of the test portion.

3.3.2.7 Saponification value

As described by (AOAC, 2000) using the official method of (920.160), melted and

filtered oil sample (5g) were placed in 250 mL Erlenmeyer. 50 mL of alcoholic KOH was

added to the flask, then the flask was connected to air condenser whiling heating in

water bath for an hour till saponification complete. After the flask and condenser have

cooled somewhat the inside of the condenser was washed using 10 ml of hot ethyl

alcohol neutral to phenolphthalein. The excess KOH was titrated with 0.5N

hydrochloric acid, using phenolphthalein as indicator. Blank was determined alongside

without oil, using same pipette for measuring KOH solution and draining same time.

39

�������������� ������ =56.1 × � × (� − �)

� Eq. [3.9]

Where:

B = Volume in ml of standard hydrochloric acid required for the blank.

S = Volume in ml of standard hydrochloric acid required for the sample.

N = Normality of the standard hydrochloric acid.

W = Weight in g of the oil taken for the test.

3.3.2.8 Viscosity

Oil sample (35–45 mL) melted at 40 0C was placed in 50 mL beaker and the viscosity

was determined using Sine-Wave Vibro Viscometer, A&D Model SV-10 made in USA.

By immersing the spindle into the oil sample up to the mark, the analysis was carried

out at a temperature of 40 0C. The viscometer was standardized using distilled water at

20 °C which is expected to be 1.002 mPa. s.

3.3.2.9 Refractive Index

The oil sample was melt and filtered through a filter paper (Whatman grade 1, 2012,

USA) to remove impurities and traces of moisture until the sample is completely dried.

Stream of water was circulated through the instrument. The temperature of the

refractometer was adjusted to the desired temperature, 400C. Cleanness and dryness of

the prisms were ensured and a few drops of the oil sample was placed on the prism.

The prisms were closed and allowed to stand for 1-2 min. The instrument and lighting

was adjusted to obtain the most distinct reading possible and determining the refractive

index. (AOAC 2000, Official method 921.08).

3.3.2.10 Determination of Crude Protein

Protein content was determined by Kjeldahl method according to the A.O.A.C official

method 920.87 (2000). About 1.0 g of filtered and dried oil was taken in a Tecator

(Model: 2300 Kjeltee Analyzer unit, Wagtech) tube and 6 ml of acids mixture (mix 100

mL of concentrated sulfuric acid with 5 mL of concentrated ortho-phosphoric acid) was

40

added, mixed, thoroughly and 3.5 mL of 30 % hydrogen peroxide was added step by

step.

As soon as the violent reaction had ceased, the tubes were shaken for a few minutes and

placed back into the Tecator rack. A 3.00 g of the catalyst mixture (ground 0.5 g of

selenium metal with 100 g of potassium sulfate) was added into each tube, and allowed

to stand for about 10 min before digestion. When the temperature of the digester

reached 420 oC, the tubes were lowered into the digester. The digestion was continued

until a clear solution was obtained for about 1 hr. The tubes in the rack was transferred

into the fume hood for cooling, 15 mL of deionized water was added, and shaken to

avoid precipitation of sulfate.

A 250 mL conical flask containing 25 mL of the boric acid-indictor solution was placed

under the condenser of the distiller with its tips immersed into the solution. The

digested and diluted solution was transferred into the sample compartment of the

distiller. The tubes were rinsed with two portions of about 5 mL deionized water and

the rinses were added into the solution. A 25 mL of 40% NaOH solution was added into

the compartment and washed with a small amount of water, stoppered and the steam

switched on. About 100 mL solution of the sample was distilled, and then the receiver

was lowered so that the tip of the condenser is above the surface of the distiller. The

distillation was continued until a total volume of 150 mL is collected. The tip was rinsed

with a few milliliter of water before the receiver was removed.

Finally, the distillate is titrated with standardized 0.1N sulfuric acid to a reddish color.

Total Nitrogen = N ×(� − B)

�× 14.007 × 100 Eq. [3.10]

Where: N = Normality of standard sulfuric acid.

T = Volume (mL) of sulfuric acid solution used in the titration.

B = Volume (mL) of sulfuric acid solution used in the titration for the blank.

W = Weight in g of sample oil.

Crude protein = Total nitrogen × 6.25 Eq. [3.11]

41

3.3.2.11 Determination of Vitamin C (Total Ascorbic acid) content

The vitamin C content of the S. birrea (marula) fruit juice was determined as to the

laboratory manual of EHNRI Food Chemistry Laboratory using Spectrophotometric

method. The reagents used were deionized water, 9NH2SO4, 85% H2SO4, 5% meta

phosphoric acid, HPO3, H3PO4, 2% 2.4-DHPH in 100 ml of 9N H2SO4, 2% Thiourea,

saturated bromine solution, 6% Trichloroacetic acid and ascorbic acid standard. The

apparatus used were: Grinder, Centrifuge, Filtration apparatus (funnel, vacuum pump,

and filter paper), pipette, test tubes, volumetric flasks, Erlenmeyer flasks (250 ml), water

bath apparatus and ice bath, and UV-Vis Spectrophotometer.

The calculation to obtain vitamin C content of the fruit juice was done using the

following formula:

mg ascorbicacid

100g=

�(������) − �(�����)

�(μ� ���) − �(�����) Eq. [3.12]

Where: A (sample) = Absorbance of the sample

A(blank) = Absorbance of the blank

A (10 µg std) = Absorbance of 10 µg standard

3.3.2.12 Mineral content determination

Major mineral contents of marula juice, P. falcatus oil and S. birrea (marula) oil were

conducted by the following AOAC methods:

Table 3.110 AOAC 2000 Mineral content analysis methods

Parameter Test method

Calcium (Ca) AOAC Official Method 923.03 - Flame AAS

Potassium (K) AOAC Official method 923.03 – Flame Photometer.

Sodium (Na) AOAC Official method 923.03 – Flame Photometer.

42

3.3.3 Sample Analysis (Gas Chromatography-Mass Spectrometry)

A Gas Chromatography (Hewlett Packard 5890 series II Gas Chromatograph) with Auto

sampler and Mass Selective Detector (Hewlett Packard 5972 series Mass Selective

Detector) and Chemstation Data System was used. Samples were injected into phenyl

methyl siloxane fused-silica capillary column (30m x 0.53mm film thickness 0.25 µm) in

the splitless injection mode. The oven temperatures were as follows: the initial

temperature was 50°C, hold 4 min. It was raised to 150°C at a rate of 15°C/min, then to

200°C at the rate of 3°C/min and followed by 8°C/min to 280°C and hold for 8 min.

Helium, as a carrier gas, was set to a column flow rate of 0.9 mL /min. Other

instrumental parameters were set as: the electron energy was set at 70eV, the ion source

temperature set at 250°C, the quadrupole temperature was 150°C, the interface

temperature was 280°C and the injector temperature set at 250°C, The sample volume

was 1µL.

A sample of 5mL of podo and marula oil extract was evaporated to dryness and

reconstituted in 200 µL n-hexane or 200 µL methanol. The extracts were then subjected

to GC-MS analysis. Compounds were identified by matching their mass spectra with

those of pure compounds whenever possible. Identification of structures/compounds of

the peaks was supported by comparison to commercial mass spectral libraries.

43

CHAPTER FOUR

RESULTS AND DISCUSSION

4.1 Marula Juice Extraction and Proximate analysis

Marula juice was extracted manually by squeezing the ripen fruit and 248 ± 5ml juice

were obtained from 1kg marula fruit.

The result showed 25% of marula fruit can be extracted to juice. Squeezing is not

efficient to gain a high juice yield, because part of the flesh is attached to the central pit

and skin. According to Gous, Weinert and van Wyk, (1988) the fleshy part of the marula

fruit contains more than 2.0% pectin. Researches showed in Namibia the use of a small

pedal-operated hydraulic press has been used and marula juice can be extracted at a

much faster rate (du Plessis, Lombard & den Adel, 2002). In some trials with a hydraulic

press, juice yields varied from less than 20% to more than 40% of the fruit weight (du

Plessis et al., 2002).

Proximate analyses of the extracted marula juice were conducted and the results are

shown in Table 4.1.

Table 4.1 Proximate analysis of marula juice

Sample Moisture % Crude fat% Crude

protein% Sugar% Ash %

Sodium

(mg/100g)

Potassium

(mg/100g)

Vitamin C

(mg/100g)

Marula

juice 89.23±0.06 0.188±0.03 4.5±0.07 5.6±0.01 0.51±0.04 1.67 ± 0.02 257.2±0.13 141.29±0.32

The result showed marula fruit juice is extremely high in Vitamin C and potassium. The

result obtained is in range of different studies. (Pretorius et al., 1985, Eromosele et al,

1991 and Hillman, et al., 2008).

The moisture content of marula juice analyzed was 89.23 ± 0.06%. Different researches

showed moisture content of marula fruit juices/flesh varies between 82 and 93% (Gous

et al., 1988 and Shone, 1979). These variations were attributed to differences in growing

44

conditions of the trees (Gous et al., 1988). In different regions of Southern Africa,

reported moisture content of marula juice/flesh varied from 79–92g/100 g. Oranges,

banana, papaya, mango and pineapple when ripe, have moisture contents of 83%, 74%,

90%, 80% and 85%, respectively (Hernandez et al., 2006).

From the analysis obtained vitamin C content of marula juice was 141.29 mg/100g.

Different studies have reported results varying as low as to 62 mg/100 g (Carr, 1957) to

more than 400 mg/100 g in the fresh fruit (Eromosele et al, 1991 and Hillman, et al.,

2008). Even the lowest reported values of vitamin C in marula are comparable to the

content of vitamin C in other fruits such as orange juice and still higher than that of

other citrus juices while recorded values that were 3 to 4 times the amounts found in

oranges juicewere reported (Mdluli and Owusu-Apenten, (2003); Glew et al., (2004); and

Nagy et al., (1990), Pretorius et al., 1985). Hillman et al., (2008) found very high content

of ascorbic acid in marula fruit juice, as high as between 700 and 2100 mg/100 g, more

than 10 times higher than in orange juice and pomegranate juice. Leakey, (1999) stated

that the vitamin C content of marula fruits in Nigeria was 403 mg/100 g, although

Eromosele et al., (1991) stated that the variation can be considerable depending on the

stage of ripening, the content being highest in ripe fruits with 403 mg/100 g and 201

mg/100 g in unripen fruits. According to Leakey (1999), the proximate analyses for

different fruits from southern Africa reveal some variation, which may be either

genetic or environmental or both and or due to different analytical methods.

Hillman et al., (2008) found the variation to be due to differences among clones of

marula and fruits ripening stages.

Most fruits such as grapes, oranges, apple, lemon and papaya amongst many others,

have a lower vitamin C content compared to marula fruit as shown in Appendix I. Only

guava has a high vitamin C content of about 300 mg/100 g (Vinci et al., 1995). As shown

in Appendix I, vitamin C content vary greatly with different studies. This could be due

to different analytical methods used, but also due to variation in the place of origin, soil,

climate, ripening stage of the fruits and time that lapsed after harvesting before analysis

45

took place. Vitamin C is an important anti-oxidant, helps protect against cancers, heart

diseases, stress, helps in maintaining healthy immune system, it aids in neutralizing

pollutants, is need for antibody production, acts to increase the absorption of nutrients

(including iron) in the gut and thins the blood, it is essential for sperm production and

for making the collagen protein involved in the building and health of cartilage, joints,

skin and blood vessels (Anon; 2004). Taylor et al. (1995) stated that the high vitamin C

content in the fruit as well as the oils and other nutrients in the nuts provide people,

especially children, with important nutritional requirements and the fruit can be used to

make chutneys and pie fillings. The juice of fruits is pleasantly acidic, sour-tasting and

refreshing (Hall et al., 2000). So the juice can serve as an important source of vitamin C.

The analysis result also showed potassium content of the S. birrea (marula) fruit juice is

high, about 257.2 mg/100g. Researches done by Shone (1979) stated it can also vary at

317 mg/100 g of fruit flesh and by Wehmeyer (1967) at 54.8 mg/100 g. This indicates

the potential of marula juice as source for potassium. As well as vitamin C, the

potassium content of marula juice is higher than that of orange 247mg/100g, tangerine

132mg/100g (Gutherie and Picciano, 1995). Potassium is an essential mineral that works

to maintain the body’s water and acid balance. As an important electrolyte, it plays a

role in transmitting nerve impulses to muscles, in muscle contraction and in the

maintenance of normal blood pressure. The daily requirement of potassium is

approximately 2000 mg and. Increased consumption of citrus fruits and juices is a good

means of increasing potassium intake. One medium orange and one 225 ml glass of

orange juice provide approximately 235 mg and 500 mg of potassium, respectively

(Whitney and Rolfes, 1999). So the result states marula juice as an important source of

potassium.

Different researches showed the importance of marula juice as a good source of

different minerals and antioxidants. Hillman et al., (2008) reported antioxidant capacity

of marula juice to be 141 – 440 mg/100 ml ascorbic acid equivalent compared to 44 – 76

46

mg/100 ml ascorbic acid equivalent for orange and 44 – 132 mg/100 ml ascorbic acid

equivalent for pomegranate.

4.2 Determination of moisture content

Moisture content of Dried S.birrea (marula) and P. falcatus seeds was obtained using

equation 3.2. The results were 8.90 ± 0.24 and 8.41 ± 0.33 forP. falcatus and S. birreaseeds

respectively.

4.3 Preliminary work

The main preliminary work carried out in this thesis project was to determine the

appropriate particle size for extraction and further analysis of S.birrea and P. falcatus

oils.

4.3.1 Selection of particle size

Three different particle sizes (<0.02mm, 0.02-0.06 mm, 0.06-1.18 mm and 1.18-2.36 mm)

were taken to determine the appropriate particle size for extraction of the oils and the

results are presented in Table 4.2.

Table 4.2 Particle size determination

Extraction time

(hr)

Moisture

content (%) Particle size (mm)

Oil yield dwb (%)

Marula oil P. falcatus oil

3 9 <0.2 43.24 ± 0.07c 41.02 ± 0.21c

3 9 0.2-0.6 59.54± 0.04d 51.13 ± 0.35d

3 9 0.6 – 1.18 23.67 ± 0.16b 27.21 ± 0.36b

3 9 1.18 - 2.36 13.55 ± 0.13a 10.35 ± 0.21a

Levels not marked by same letter across a column are significantly different (p<0.05)

Effect of particle size on oil yield

Particle size plays a great role on the yield of both S. birrea (marula) and P. falcatus oils.

Smaller particle size gives high yield while samples with large particle size deliver low

yield. That means less oil is extracted from the larger particles (above 0.6 mm)

compared to the small size of the particles. The reason is that larger particles with

47

smaller contact surface area, have more resistant to solvent entrance and oil diffusion

towards the solvent. Therefore, less amount of oil will be transferred from inside the

larger particles to the surrounding solution in comparison with the smaller ones. Thus,

an increase in particle size will decrease the oil yield (T. Suganya et al 2012).

Besides size reduction of the plant material avail the extractable component by breaking

of the cellular storage structure of the cell components and the cell wall of the plant

material and make close to the site of accumulation. Similar reports were made for

different materials and purpose where smaller size enhance the extraction of oil from

oilseeds (Russian et al. 2007, Olaniyan 2007, Meziane et al. 2006, Ebeweleet al. 2010).

From this study realized that a particle size of 0.2-0.6mm gave better oil yield therefore

all analysis this particle size was selected.

Nevertheless, we know that when the particle is too small (very fine particle size), the

extracted oil become small in its amount, even though the contact surface area for small

particle is supposed to be significantly higher than that for the larger particles. This may

be due to the agglomeration of the fine particles which reduces the effective surface area

available for the free flow of solvent towards inside the solid particles.

4.4 Soxhlet Extraction

4.4.1 Percent yield of soxhlet extractor

Based on the preliminary work result a particle size of 0.2-0.6 mm is selected for both S.

birrea and P. falcatus samples and the effects of moisture content and extraction time on

yield of the oils were studied.

The yield was calculated by using equation 3.3 and shown in Table 4.3

48

Table 4.3 Total % yield for soxhlet extractor for different moisture contents and extraction times

Moisture Content (%) Extraction time (hours) Yield (%)

S. birrea (Marula) P. falcatus

9

2 43.21±0.05a 37.27±0.01a

3 59.54±0.04b 51.13±0.35c

4 59.53±0.02b 50.86±0.04c

12

2 43.71±0.03a 43.88±0.03b

3 61.36±0.05c 58.63±0.02d

4 61.35±0.04c 58.15±0.07d

15

2 43.64±0.02a 33.29±0.04a

3 59.02±0.06b 47.66±0.02e

4 58.89±0.06b 47.62±0.06e

Levels not marked by same letter across a column are significantly different (p<0.05)

4.4.2 Effect of extraction time on percent yield of oil

Extraction time plays a great role on the yield of S. birrea (marula) and P.falcatus oil

using n-hexane as a solvent. Figures 4.1 (a), (b), and (c) and Figures 4.2 (a), (b) and (c)

show that as the contact time increases the oil yield also increases this continues till

transfer of oil from the kernel powder to the solvent attains zero. In other word, when

the maximum amount of extractable oil is obtained, the oil yield level remains

invariable even by extending the reaction time. So that in the soxhlet extraction the

maximum oil yield could be finding at an extraction time of 3 hours and above. As

shown graph of Figure 4.1 and Figure 4.2, extracting the oil beyond three hours doesn’t

bring an increment on yield therefore using n-hexane as a solvent maximum yield

attained at the specified time.

The extraction rate is fast at the beginning of the extraction but gets slow gradually. The

reason is that when the kernel powder is exposed to the fresh solvent, the free oil on the

49

surface of seeds is solubilized and oil gets extracted quickly inducing a fast increase in

the extraction rate.

Furthermore, since the oil concentration is low in the solvent at the beginning of the

extraction process, the oil diffuses quickly from the kernel to the liquid phase due to the

difference in concentration (driving force) of the oil. As the time passing by, the

concentration of oil increases in the solvent resulting in a decrease in the diffusion rate.

(a) (b)

(c)

Figure 4.1The effect of time on marula oil yield at moisture content (a) 9%, (b) 12 % and (c) 15%

3035404550556065

2 3 4

Yie

ld (

%)

Extraction time (hr)

3035404550556065

2 3 4

Yie

ld (

%)

Extraction time (hr)

3035404550556065

2 3 4

Yie

ld (

%)

Extraction time (hr)

30

35

40

45

50

55

60

65

2 3 4

Yie

ld (

%)

Extraction time (hr)

30

35

40

45

50

55

60

65

2 3 4

Yie

ld (

%)

Extraction time (hr)

50

(a) (b)

(c)

Figure 4.2 The effect of time on P. falcatus oil yield at moisture content (a) 9%, (b) 12 % and (c) 15%

4.4.3 Effect of particle moisture content on oil yield

Finally, the effect of moisture content on oil yield reveal that 12% produce high yield

(61.33% and 58.63%). At 9%moisture content the oil yield increases (53.73% and

51.13%). When the moisture content is 15%, oil yield reduces to 49.66% and 47.66 %

respectively for marula and P. falcatus as shown in Table-4.3 in the above result.

High moisture content hinder oil flow possibly because the structures of the finely

milled particles have been altered (high aggregation) (Sefah, 2006). Also other

researches revealed hexane is highly insoluble in water; hence, with high moisture

content the extraction efficiency of the solvent will be drastically reduced, therefore

poor oil yield results (Lawson O. S et al 1999).

The following tables (Table 4.4 and 4.5) shows analysis of variance (ANOVA), this will

tell us the significance of different factors.

30

35

40

45

50

55

60

65

2 3 4

Yie

ld (

%)

Extraction time (hr)

51

Table 4.4 ANOVA results for an experiment in soxhlet extraction of marula oil

Source Sum of

Squares

Degree of

Freedom

Mean

Square F value

P-value

Prob>F

Model 2499.73 8 312.47 760.05 <0.0001

A-Time 1686.84 2 843.42 2051.56 <0.0001

B-Moisture Content

811.03 2 405.51 986.39 <0.0001

AB 1.86 4 0.47 1.13 0.3726

Table 4.5 ANOVA results for an experiment in soxhlet extraction of P. falcatus oil

Source Sum of

Squares

Degree of

Freedom

Mean

Square F value

P-value

Prob>F

Model 1751.54 8 218.94 1978.73 <0.0001

A-Time 1212.43 2 606.21 5478.75 <0.0001

B-Moisture Content

538.27 2 269.13 3432.33 <0.0001

AB 0.85 4 0.21 1.92 0.1509

The Model F-value of 760.05 and 1978.73 implies the model is significant. Values of "Prob >

F" less than 0.0500 indicate model terms are significant. In this case A-time, B-moisture

content are significant model terms. Values greater than 0.1000 indicate the model terms are

not significant. The P-value of AB (interaction factors) is 0.3726>P-value for marula oil and

52

0.1509 for P. falcatus thus, the interactions of moisture content and time are not significant in

the model terms.

Figure 4.3 below shows that there are no interactions among each factors. This shows us

an increment in time will increase the quantity of oil extracted but beyond three hours

didn’t give a significant change on oil yield.

(a) (b)

Figure 4.3 Effects of time, moisture content and their interactions on (a) marula (b) P. falcatus oil yield

Design-expert was applied to analyze results on the extraction process and a second

order regression equation, with the interaction terms, of the form:

% Marula Yield = +49.58 - 11.18 * A[1] + 5.67 * A[2] - 1.27 * B[1] + 7.26 * B[2+ 0.20 * A[1]B[1] – 0.24 * A[2]B[1] + 0.28 * A[1]B[2] - 0.17 * A[2]B[2]

% P. falcatus Yield = +47.62 - 9.48 *A[1] + 4.85 * A[2] - 1.20 * B[1] + 5.97 * B[2] + 0.33 *

A[1]B[1] - 0.14 * A[2]B[1] - 0.24 * A[1]B[2] + 0.19 * A[2]B[2]

From the equation deduced that the individual effect of time (A) and particle sizes (B)

as parameter showed higher value irrespective of their sign whereas their interactions

53

in the entire extraction process was found to be insignificant. Therefore, the final

equation in terms of coded factor without the interaction effect is given by first order

regression.

Diagonstics

The following Figure 4.4 shows the relation between the actual value of the experiment

and the value predicted by the model equation developed by the Design Expert

software.

Figure 4.4 Predicted vs. actual value of yield for soxhlet extraction (a) marula oil (b) P. falcatus oil

The residue for equation (4.2) that will describe the difference between the actual values

of the model and the predicted one was shown in the following Table 4.6 and 4.7.

54

Table 4.6 Difference between the actual (experimental) value and predicted value for marula oil yield

Standard Order Actual Value Predicted Value Residual

1 63.10 62.33 0.77

2 49.80 49.67 0.13

3 49.60 49.17 0.43

4 37.20 37.33 -0.13

5 54.10 53.87 0.23

6 54.10 53.73 0.37

7 63.10 62.23 0.87

8 46.00 45.93 0.067

9 37.80 37.33 0.47

10 45.70 45.93 -0.23

11 61.20 62.23 -1.03

12 62.00 62.33 -0.33

13 48.80 49.17 -0.37

14 53.90 53.87 0.033

15 33.20 31.93 1.27

16 49.10 49.17 -0.067

17 53.60 53.87 -0.27

18 50.20 49.67 0.53

19 53.20 53.73 -0.53

20 62.40 62.23 0.17

21 31.00 31.93 -0.93

22 49.00 49.67 -0.67

23 31.60 31.93 -0.33

24 53.90 53.73 0.17

25 37.00 37.33 -0.33

26 61.90 62.33 -0.43

27 46.10 45.93 0.17

55

Table 4.7 Difference between the actual (experimental) value and predicted value for P. falcatus oil yield

Standard Order Actual Value Predicted value Residual

1 58.11 58.22 -0.11

2 51.26 51.27 -8.519E-003

3 33.22 33.38 -0.16

4 50.45 51.05 -0.60

5 50.54 51.05 -0.51

6 43.85 44.12 -0.27

7 47.81 47.48 0.33

8 51.47 51.27 0.20

9 47.86 47.70 0.16

10 58.48 58.22 0.26

11 58.21 58.22 -9.630E-003

12 43.98 44.12 -0.14

13 58.12 58.44 -0.32

14 47.45 47.48 -0.033

15 58.90 58.44 0.46

16 58.87 58.44 0.43

17 50.65 51.27 -0.62

18 51.60 51.05 0.55

19 33.53 33.38 0.15

20 37.02 36.94 0.076

21 43.81 44.12 -0.31

22 37.35 36.94 0.41

23 47.47 47.70 -0.23

24 47.64 47.70 -0.064

25 37.44 36.94 0.50

26 33.12 33.38 -0.26

27 47.60 47.48 0.12

56

4.5 Physico-chemical characteristics

Some physical and chemical properties of marula and P. falcatus oil extracted are

shown in Table 4.8.

Table 4.8 Physico - Chemical properties of S. birrea (marula) and P. falcatus oil

S. birrea oil P. falcatus oil

Color Light yellow Light yellow

Odor Nuttish -

Refractive index 1.467 1.47

Viscosity mm2/s 38.2 41.22

Specific gravity at 15 0C 0.899 0.90

Peroxide value mEq/kg 4.2 4.4

Acid value 3.6% 4.0

Free fatty acid 1.81 2.06

Saponification value

mg/KOH

190 189.1

4.5.1 Specific gravity

Specific gravity also referred to as relative density is an important physical character

that can give information on the identity of the sample as well as detect adulteration of

oils of which density may increase or decrease. It can also provide information for

loading on the weight of the oil from the given volume while exporting it in large

volumes (Hamilton et al, 1986).

The specific gravity of 0.899 for marual oil is in accordance with the specific gravity of

0.90 obtained by (I. Vermaak et al. 2011), 0.92 (Shone 1979), 0.91 (Lightlem et al. 1951)

higher than (0.88) a result obtained by (Ejilah Robinson et al 2012).

57

The specific gravity of 0.90 for P. falcatus oil was similar with the specific gravity of 0.90

obtained by (Feleke S. et al 2012).

The specific density (0.899 and 0.90) of marula and P. falcatus oils respectively agreed

well with the data reported for edible oil of common oil seeds (0.91–0.93) such as niger,

rapeseed, linseed, sunflower, watermelon seed kernel oil (0.92), Sterculiastriata

(0.85),Weinert et al., 1990and shea butter oil (0.92) (Seegler 1983, Nag & De 1995,

Onyeinke & Acheru 2002,). Specific gravity indicates the purity of oil.

4.5.2 Refractive Index

Refractive index is the ratio of the speed of light in a vacuum to that in the oil under

examination which is related to the degree of unsaturation and the ratio of cis/trans

double bonds, and can also provide hints on the oxidative damage (Hamilton et al.,

1986). Refractive index can be used for rapid sorting of fats and oils which are suspected

to be adulterated (Olaniyan et al, 2007) as well as one of the important physical

characteristics for identification of oils and fats. Refractive indices of natural fats and

oils are related to the degree of unsaturation and with saponification value of the oil

(Rudan-Tasic & Klofutar 1999, Gerhard 2002). In this study, refractive index was

measured for both marula and P. falcatus oils and the average results are 1.467 and 1.47

respectively, the result obtained for marula oil was in accordance with the results

obtained (1.46) by (Shone 1979 and, Lightlem et al. 1951). The refractive index of P.

falcatus oil (1.47) is in accordance with the result (1.47) obtained (Feleke S. et al 2012).

The results obtained are similar to those of common niger (1.46–1.48) and watermelon

(1.47) seeds (Nkafamiya et al. 2007).

4.5.3 Viscosity

Oils containing fatty acids of low molecular weight are slightly less viscous than oils of

high-molecular-weight acids (Hidalgo, F.J, 2005). The viscosity measured at 400CforS.

birrea andP. falcatus oil was found to be (38.2 mPas) and (41.22 mPas) respectively and

when compared with sesame (57.0 mPas), groundnut (65.7 mPas) and sunflower (62.1

58

mPas) oils (Mariod, A et al, 2009) but higher than that of palm oil (34.7 mm2/s), soya oil

(25.0 mm2/s), groundnut oil (24.7 mm2/s) and cotton oil (18 mm2/s) (Ejilah I R, 2012)

these oils are less viscous. The obvious difference between the viscous behavior marula

and P. falcatus kernel oils could be attributed to higher “van der waals” forces acting

among oil molecules, molecular weight of the fatty acid and the types of carbon chain

presented in the oils (Looney R T, 1975).

4.5.4 Acid value and free fatty acids

Acid value corresponds to the amount of potassium hydroxide needed to

neutralize free fatty acid. The lower the acid value of an oil, the fewer free fatty acids it

contains which makes it less exposed to the phenomenon of rancidification (Roger et al.,

2010). The acid value obtained for marula oil is 3.6 and 4.0 for P. falcatus which is in

accordance to the result obtained (3.7) by (Shone 1979), and much smaller than 14.8

(Lightelm et al 1951) for marula oil while that of other edible oils such as

Amaranthushybridus is (2.84). Acid value varies according to the extraction method -

Soxhlet (Horowitz, 1948), Bligh and Dyer (Bligh and Dyer, 1959) and Folch (Omoti and

Okyi, 1987) (Folch et al., 1957) with high acidity by soxhlet method due to the onset of

oxidation (Codex, 1993). Low acid value implies a rather stable oil at the extraction

temperature (Codex, 1993). The lower the acid value of oil, the fewer free fatty acids it

contains which make it less exposed to the phenomenon of rancidification (Roger et al.,

2010). So the result suggest the oils are stable.

4.5.5 Saponification value

The saponification value helps to determine the quantity of potassium (in mg) needed

to neutralize the acids and saponify the esters contained in 1g of lipid (Roger et al.,

2010). The saponification value (190 mg/KOH and 189.1 mg/KOH) obtained for marula

and P. falcatus oils respectively is lower than those of the common oils such as soyabean

(189-195 mg/KOH), Peanut (187 - 196 mg/KOH) and cotton seed oil (189-198

mg/KOH) (Codex, 1993) and olive oil (185-196 mg/KOH) (Anhwange et al., 2010).

59

The saponification value obtained for marula oil is in accordance with the result (162.70-

193.50 mg/KOH) obtained by (I. Vermaak et al., 2011), (180-189 mg/KOH) (P. Zharare

et al, 2000) and 178.6 mg/KOH (Ejilah Robinson et al 2012). Also the saponification

value of 189.1 mg/KOH for P. falcatus oil is in accordance to the result (189.3 mg/KOH)

obtained (Feleke S. et al 2012).

High saponification value of fats and oils are due to the predominantly high proportion

of shorter carbon chain lengths of fatty acids (Gohari, A.A. et al; 2011). Low molecular

weight (short to medium chain) fatty acids have more glyceride molecules per gram of

fat than high molecular weight acids. Each glyceride molecule requires three KOH

molecules for saponification, hence the more the glyceride molecules the greater the

saponification value (Kirk, R.S. et al, 1991) as cited in (Aurand, L.W. et al, 1987).

According to Nagre, R.D. et al, (2011), saponification value in combination with the acid

value provides information on the quantity, type of glycerides and mean weights

of the acids in a given sample. Saponification value is of interest if the oil is for

industrial purposes, as it has no nutritional significance (Dari, L., 2009). The larger the

saponification number, the better the soap making ability of the oil (Asiedu, J.J., 1989).

So the oils could be used for the manufacturing of soap.

4.5.6 Peroxide value

The peroxide value obtained (4.2 and 4.4 mEq/kg) for marula and P. falcatus oil

respectively is similar with a number of conventional oils e.g. amaranthushybridus

(Codex, 1993) but higher than that of cotton seed oil of 2.5 mEq/kg(Popoola T O S et al,

2006) and Schinziophytonrautanenii of 2.51 mEq/kg (I. Vermaak et al 2011).

The peroxide value is the measure of oxidative rancidity of oil. Oxidative rancidity is

the addition of oxygen across the double bonds in unsaturated fatty acids in the

presence of enzymes (Ekpa and Ekpa, 1996). The odour and flavour associated with

rancidity are due to the liberation of short chain carboxylic acids. High peroxide values

are associated with a higher rate of rancidity. Variation of peroxide value could be due

60

to the level of unsaturated fatty acid content, since the rate of auto-oxidation of fats and

oils increases with increasing levels of unsaturation. Low peroxide values of oils

indicate that they are less liable to oxidative rancidity at room temperature

(Odoemelam, 2005; Anyasor et al., 2009). Freshly extracted edible oil is expected to have

an acceptable shelf life, i.e. 5–8 years. This means its peroxide value should be less than

5 meq kg (Gunstone 1999, Rudan-Tasic & Klofutar 1999). So from the result obtained it

could be concluded the extracted oils are less liable to oxidation and will have longer

shelf life.

4.5.7 Fatty acid composition

The total fatty acid composition of the extracts obtained in this study was determined

by GC-MS and is shown in Table 4.9 and Appendix III. The fatty acid profile is a main

determinant of the oil quality. The extracted marula and P. falcatus oil contained major

fatty acid compounds were oleic and stearic acids. It can be seen that most of the values

for marula oil fall within the ranges published in the literature (P. Zharare et al, 2000,

Ejilah Robinson et al 2012).

S. birrea and P. falcatus oil contains a large proportion of monounsaturated fatty acids.

The result presented the fatty acid composition of S. birrea (marula) oil as mono-

unsaturated oleic acid (73.6%), poly-unsaturated linoleic acid (6.1%), linolenic acid

(0.3%), saturated palmitic acid (12.8%), and stearic acid (7.2%). And for P. falcatus mono-

unsaturated oleic acid (78.94%), poly-unsaturated linoleic acid (4.7%), linolenic acid

(3.04%), saturated palmitic acid (8.87%), and stearic acid (4.45%). It is, however,

important to note that the high percentage of mono-unsaturated oleic acid provides a

high degree of oiliness. Acids degree of unsaturated fatty acid leads to solidification at

low temperature or cloud formation.

Oils rich in monounsaturated FAs (e.g. oleic acid) are generally more stable to oxidative

rancidity and stable as deep frying oils (Mohammed et al., 2003). They have many

applications such as plant based lubricants and as feedstock for the oleochemical

61

industry (Gunstone, 1996). As a fat, oleic oil is one of the better known ones for

consumption and from a health standpoint, it exhibits further benefits of low total

cholesterol, to slow the development of heart disease and promotes the production of

antioxidants (Pérez-Jiménez et al., 2002). The high percentage of oleic acid in oil used as

indicative as a good moisturizer in soap and cosmetic industry (Ellis-Christensen, 2009).

The combination of the oiliness property, the natural propensity for soap formation (i.e.

high saponification tendency), greater affinity towards metal surfaces, and fairly high

viscosity could be exploited to minimize metal to metal contact, control temperature,

improve the lubricity and reduce wear of vital engine components under boundary and

hydrodynamic lubrication conditions. Hence, this property of marula oil makes it

suitable as a bio-lubricant resource.

Table 4.9 Fatty acid composition of S. birrea (Marula) and P. falactus oils

Fatty acid Composition (%)

Saturation level S. birrea oil P. falcatus

Palmitic acid (16:0) 12.8 8.87 Saturated

Stearic acid (18:0) 7.2 4.45 Saturated

Oleic acid (18:1) 73.6 78.94 Mono-unsaturated

Linoleic acid (18:2) 6.1 4.70 Poly-unsaturated

Linolenic acid (18:3) 0.3 3.04 Poly-unsaturated

62

CHAPTER FIVE

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

The intention of this study was to find the effect of particle moisture content and

particle size on Sclerocaryabirrea (marula) and Podocarpusfalcatus, the widely unknown

but community utilizing species, oils yield and determine the optimize solvent

extraction condition. It was found that the optimal extraction time and particle moisture

are 3 hours and 12% respectively for both seeds. Extraction beyond 3hours doesn’t add

value to oil yield because maximum yield was found at 3 hours of extraction process

and increasing the moisture content beyond 12% decreased the oil yield because the

structures of the finely milled particles have been altered and with high moisture

content the extraction efficiency of the solvent was drastically reduced. The seeds of two

plants analyzed had higher oil contents, 61.36% and 58.63% for S. birrea and P. falcatus

respectively, than those of olive seed, soybean and palm walnut. With this comparison

it can be concluded that, based on their oil content these plantshave the potential to be

domesticated as an economic source of oil.

The study also evaluatedphysico-chemical properties andfatty acid profile of the

extracted oils.Both S. birreaandP. falcatus kernel oil hadgood physicochemical properties

in comparisonwith common edible oil crops. Therefore, theycould be used in the

production of edible oil,value-added productsand potential raw material for cosmetics,

soap, and in thebakery/confectionery sector. The production ofoil from these trees and

its popularizationto other areas may directly contribute to incomegeneration of the

community besides contributes to the carbon trade and reduction in global climate

warning.

Additionally it can be concluded from the result obtained that marula juice is a very

good source of vitamin C and minerals like potassium.

63

5.2 Recommendations

Based on the findings of the study, the following recommendation can be made in order

to extendthe range of use of the oils:

The oils extracted from selected seed trees should be refined and determine the

characteristics and fatty acid composition of these refined oils, because refining

bring improvement in the quality of the oil by removing variable impurities.

Creating better cracking and exposing of the kernels from marula nut need to be

studied to facilitate rate and quantity of oils to be extracted.

Awareness should be created

Before commercializing these invaluable plant oils:

o Economic analysis has to be conducted in detail

o Other extraction methods needs to be analyzed and compared to solvent

extraction method prior to commercialization

o Other parameters which will affect quality and quantity of the oils need to

be conducted.

o Comparison of oil yield and quality from different locations should be

conducted.

64

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APPENDICES

Appendix I Vitamin C content of marula fruit in comparison to some fruits

Type of fruit Vitamin C (mg/100 g) Source

Pulp Flesh/Juice

Marula 62-179.1

403 200 275 267 133

Eromosele et al, (1991) Nerd, et al,(1990) Carr (1957) Borochov-neori et al, (2008) Dlamini and Dube, 2008

Orange 50 60 33

Eromosele et al, (1991) Tekeda 2009 Dlamini and Dube, 2008 Hillman et al, 2008

Strawberries 60 Eromosele et al, (1991) Takeda, 2009

Grapes 38 Eromosele et al, (1991)

Guava 300 Takeda (unknown year)

Baobab 283 Chadare et al, 2009

Parinari mobola (hissing tree) 64.1 Carr (1957)

Kiwi 52 67

Hillman et al, 2008 Vinci et al, 1995

Wild grape (Lannea edulis) 14 Carr (1957)

Sour plum (Ximenia caffra) 49.2 Carr (1957)

Wild mango (cordyla Africana) 75.6 Carr (1957)

Avocado pear 10 Vinci et al, 1995

Kumquat 55 Vinci et al, 1995

Litchi 22 Vinci et al, 1995

Mango 25 Vinci et al, 1995

Papaya 88 Vinci et al, 1995

Passion fruit 65 Vinci et al, 1995

Pineapple 25 31

Takeda, 2009 Vinci et al, 1995

Apple 6 Takeda, 2009

Lemon 50 51

Takeda, 2009 Vinci et al, 1995

Apricot 25 Takeda, 2009

Cantaloupe 40 Takeda, 2009

Cherry 6.5 Takeda, 2009

Grapefruit 45 65

Takeda, 2009 Vinci et al, 1995

Peach 7 Takeda, 2009

Tomato 25 Takeda, 2009

74

Appendix II Sample collection, pretreatments and laboratory work

Figure I-1 Pretreatments: A: Data location of S. birreaB: Size reduction C: Sieving D:Weighing

A

B C

D

75

Figure I-2 (A) Solvent extraction (B) Extracted S. birrea oil (C) Extracted P. falcatus oil

Figure I-3Laboratory work: Saponification value (A&B); Specific gravity(C)andTitration

(D)

A

B C

76

Appendix III GC-MS analysis (A) Podocarpusfalcatus (B) Sclerocaryabirrea

A

77

B