Avocado Proximate analysis

Avocado

Scientific Name : Persea Americana

Scientific classificationKingdom PlantaePhylum AngiospermsOrder LauralesFamily LauraceaeGenus PerseaSpecies P. Americana

Binomial namePersea americana

Mill

SynonymsPersea gratissima

Origin:

The avocado probably originated in southern Mexico but was cultivated from the Rio Grande to central Peru before the arrival of Europeans.

Introduction :

Avocados are a commercially valuable fruit and are cultivated in tropical climates throughout the world, producing a pear-shaped fruit that ripens after harvesting. It grows up to 20 m in height and may be equally wide. Leaves are arranged spirally. Flowers are small.

The skin may be yellow-green, deep-green or very dark-green, reddish-purple, or so dark a purple as to appear almost black, and is sometimes speckled with tiny yellow dots.

Avocado is consumed mostly as a fresh fruit. In recent years, there has been a significant increase in the export of avocado fruit due to its dietary value. It is a high fat fruit, which contains rare sugars of high carbon number and is relatively rich in certain vitamins,

minerals, and nitrogenous substances. It is a high oil and low sugar content, so it is recommended as a high energy food for diabetics.

Avocado is one of the most nutritive among fruits. The fruit is high in fat, proteins, and minerals but low in carbohydrates. The fatty acid composition of lipids of avocado fruit and avocado oil differs greatly with cultivator, stage of ripening, anatomical region of fruit, and geographical location. However major fatty acid is always oleic acid followed by palmitic acids and linoleic acid. The fatty acids present in trace amounts are myristic, stearic, linoleic and arachidonic. Avocados are rich in vitamin B6, and contain lesser amounts of biotin, folic acid, thiamin, riboflavin, calciferol (vitamin D ) , alpha- tocopherol (vitamin E) and vitamin K.

Avocados are high in valuable fats and appear to have a beneficial effect on blood serum levels. For a typical avocado:

About 75% of an avocado's calories come from fat, most of which is monounsaturated fat.

Avocados also have 60% more potassium than bananas. They are rich in B vitamins, as well as vitamin E and vitamin K.

Avocados have a high fiber content among fruits - including 75% insoluble and 25% soluble fiber.

A fatty triol (fatty alcohol) with one double bond, avocadene (16-heptadecene-1,2,4-triol), is found in avocado.

High avocado intake has been shown to have a beneficial effect on blood serum cholesterol levels. Specifically, after a seven-day diet rich in avocados, hypercholesterolemia patients showed a 17% decrease in total serum cholesterol levels. These subjects also showed a 22% decrease in both LDL (harmful cholesterol) and triglyceride levels and 11% increase in HDL (helpful cholesterol) levels.

Nutritional chart: Serving Size: 100g Avocados, raw, all commercial varieties

Elements Amount

Total Calories 160 kcal

Total Fat 14.65 g

Saturated Fatty Acids 2.12 g

Monounsaturated Fatty Acids 9.79 g

Polyunsaturated Fatty Acids 1.81 g

Sodium 7 mg

Total Carbohydrates 8.52 g

Dietary Fiber 6.69 g

Sugar 0.66 g

Protein 2 g

Water 73.23 g

Vitamin C 10 g

Riboflavin 0.12 mg

Niacin 1.73 mg

Pantothenic Acid 1.38 mg

Vitamin B6 0.25 mg

Vitamin B12 0 mcg

Folate 81 mcg

Vitamin A 146 IU

Vitamin E 2.06 mg

Vitamin K 21 μg

Folic Acid 0 mcg

Calcium 12 mg

Iron 0.55 mg

Magnesium 29 mg

Phosphorus 52 mg

Potassium 485 mg

Sodium 7 mg

Zinc 0.63 mg

Copper 0.18 mg

Manganese 0.14 mg

Selenium 0.4 mcg

Ash 1.04

Source - Horticulture Research and Development Institute, Kandy, sri lanka

Ash - fromESHA foods database

Sri Lankan Avocado varieties

Although there are hundreds of Avocado Varieties throughout the world, In Sri Lanka we can find out mainly six Varieties of avocado.

FuertePollockTower-2SimmondsBooth 7Hass

Fuerte

Pear-shaped Medium seed Great taste Smooth thin green skin Creamy, pale green flesh

Size: Medium to large fruit, ranging from 150 to 420 grams

Hass

Distinctive for its skin that turns from green to purplish-black when ripe, the Hass is the leading variety of California avocado and has an excellent shelf life.

Description:

Oval-shaped fruit Small to medium seed Great taste Pebbly, thick but pliable skin

http://www.picsearch.com/imageDetail.cgi?id=1ssw6k2GCraKFSRYQe39HO611pyPouHrLLBgaf9FhzU&width=1362&start=1&q=Hass%20Avocado%20photo

Pale green flesh with creamy texture

Size: Full range from average to large, 150 to 350 grams

Booth 7

The fruit is commercially popular and the tree is a good bearer. Shape is round obovate and fruit apex is rounded. Skin is slightly rough, thick, brittle. Flesh contains 7 to 13% oil. medium sized and skin is bright green.

Season: late (Dec. to mid-Jan.).

Pollock

oblong to pyriform with rounded base, pedicel insertion is asymmetrical; medium to large size, 14-50 oz, skin green to dark green, smooth, thin, glossy; flesh of excellent quality, 78%

edible flesh, oil content, 4-8%; seed medium large, often loose in cavity; harvested late June to September.

Simmonds

Obovate shaped fruit, fruit flattened obliquely toward apex on one side, medium to large size, 16-34 oz; skin light-green to green, smooth, glossy; flesh of good to excellent quality, 76% edible pulp, oil content 3.5-5.0%; seed medium size, tight in cavity; harvested late June to mid-September.

Tower 2

medium size, green colour skin, smooth, flesh of good to excellent quality, oil content is 18 -26 %; seed medium size, Fruit Size: 1-1.5 lbs. (16-24oz), tight in cavity; harvested late August to mid-September

For this analysis series I selected avocado as my anlysing fruit. And among those varities I selected Booth 7 variety and samples of that variety was used to carry out my experiments.

Booth 7 variety

Determination Of Moisture Content.

For the determination of moisture content in avocado sample, Oven drying method was used.

Samples before oven drying Samples after oven drying

Materials :

Moisture dishes

Oven maintained at 105oC

Weighing Balance

Avocado sample

Procedure :

An avocado fruit was taken and peel and seed were removed. Then it was cut into

small cubes and the cubes were mixed well in order to select a homogenized sample. To the

nearest milligram, about 5g of the avocado cubes were weighed into a moisture dish which

was cleaned, dried and weighed previously. The uncovered dish with the lid along the side

was dried at 105oC for 3 hours. After that, the dish was covered and transferred to the

desiccator and the weight was measured quickly as soon as the dish is cool. The heating and

weighing was repeated until successive weights do not differ by more than one milligram.

The same procedure was repeated twice.

Data

Weight of empty dish /g

(m1)

Weight of the sample /g

Weight of dish + sample before drying /g (m2)

Weight of dish + sample after drying / g

(m3)

1 46.90 5.05 51.95 48.10

2 45.44 5.06 50.50 46.72

3 44.64 5.10 49.74 45.90

Calculation

Moisture percentage % m/m = Weight lost

Weigh t of t hesample

= (m 2−m 3)(m2−m 1)

M1 = Weight of empty dish

M2 = Weight of dish + sample before drying

M3 = Weight of dish + sample after drying

Sample1

Moisture percentage in sample No . 1 = 51.95−48.1051.95−46.90 ×100%

= 76.24 %

Moisture percentage in sample No . 2 =50.50– 46.7250.50– 45.44 ×100%

= 74.70%

Moisture percentage in sample No . 3 =49.74−45.9049.74 – 44.64 ×100%

= 75.29 %

Average amount of moisture percentage in avocado =76.24+74.40+75.29

3

= 75.31 %

Amount of total solid percentage in avocado = (100 – 75.31) %

= 24.69 %

Discussion

In determination of moisture content of avocado sample, oven drying method was used. Water is removed due to heating at 105 °C for 3 hours. Loss of weight due to vaporization of water is taken as weight of moisture.

The accuracy of results of moisture determination is affected by

drying temperature relative humidity particle size of sample handling method of sample amount of sample type of evaporation dish variation in temperature inside the oven Time

To minimize these errors various precautions were taken. Eg : sample was dried in stainless steel containers, which is not decompose during heating. Three consecutive samples were carried out to eliminate the errors of the handlers, usually 5 g of ground sample was taken to facilitate the drying, and this encourages the evaporation because particle size is small. Heating and weighing were repeated until successive weights don’t differ by more than 1 mg. Before weighing the sample, dish was transferred in to the decicator. It was weighed as soon as dish is cooled because temperature of the dish can affect the reading.

Avocado contains less amount of sugar (0.66g / 100g), so oven drying method is suitable for the determination of moisture to avoid caramelisation.

According to the data bases moisture content of avocado is 73.23g / 100g . But through this practical, moisture content was determined as 75.31 / 100g. So there is a difference in standard moisture content value and the observed value.

According to the environment (soil, humidity, water level in soil etc.) moisture content can be varied.

There can be determinate or systematic errors like experimental errors and instrumental error like measuring the weight.

May be pieces of avocado were larger in size.

Conclusion

Percentage of moisture content of the avocado sample is 75.31 %.

Percentage of total solid of the avocado sample is 12.76 %.

Determination of free Fat content of Avocado.

Materials :

Dried avocado saple Soxhlet extraction apparatus

Round bottom flask Condenser

Filter papers to make thimbles Mortar and pestle

Hot water bath Heating mantle

Weighing scale Dying oven

Cotton wool Pumice chips

Chemicals :

Anhydrous Sodium Sulphate

Petroleum ether

Procedure :

Dried powdered avocado sample was taken and about 5 g of the sample was added to the

mortar and ground with twice the weight of anhydrous Sodium Sulphate.

An extraction thimble was prepared using a filter paper and all powdered material in the mortar

were added to that thimble and covered with cotton wool. The extraction thimble which

containing the sample was placed in the soxhlet apparatus.

A clean and dry round bottom flask was taken and some pumice chips were added to it. Then the

weight of the flask, with the pumice chips was measured. Then 200ml of petroleum ether was

added to the flask. Then the flask was connected to the soxhlet extractor and the condenser was

fixed. While maintaining a low heating rate, it was refluxed for 5 hours.

Once the refluxing is over, the solvent was distilled off and the flask (with the contents) was

placed in an oven at 105oC for 20 minute. Then it was cooled for 30 minutes and after cooling

the weight was measured. The flask and the contents were dried until a constant weight was

observed and the weight was recorded.

Data :

Sample No. Weight of the sample / gWeight of the round

bottom flask and chips / g

Weight of the round bottom flask + fat + chips /

g

1 5.0350 95.30 97.14

2 5.0107 274.33 276.19

3 5.0431 95.54 97.35

Calculation :

Crude fat percentage = X - F x 100%

W

X = Weight of the flask with fat and chips

F = Weight of the flask and chips

W = Weight of the sample

Determination of free fat percentage in dry basis

Sample No. 1

Free fat percentage of the avocado sample = 97.14 – 95.30 x 100%

5.0350

= 36.54 %

Sample No. 2

Free fat percentage of the avocado sample = 276.19 – 274.33 x 100%

5.0107

= 37.12 %

Sample No. 3

Free fat percentage of the avocado sample = 97.35 – 95.54x 100%

5.0431

= 35.97 %

Average value of the percentage of free fat = ( 36.54 + 37.12 + 35.97 ) %

content of the avocado sample (on dry basis) 3

= 36.54 %

Determination of free fat percentage in wet basis

Average percentage of moisture content in avocado = 75.31 %

Percentage of nutrient on wet basis = Percentage on dry basis x (100 - % of moisture)

100

Percentage of free fat on wet basis = 36.54 x (100 – 75.31 )

100

= 9.02 %

Percentage of free fat content of the avocado sample on wet basis is 9.02 %

Discussion :

For the determination of free fat percentage in avocado, soxhelt method was used in this experiment.

As the extraction solvent, here petroleum ether was used and sample in the chamber slowly fills with warm solvent and then fat will dissolve in warm solvent. Since petroleum ether is highly

inflammable, special care should be taken when handling the equipments.

previously dried and powdered avocado sample was used. So, the free fat content was first

determined on dry basis and then it was converted to wet basis.

Extraction thimble was prepared using a filter paper according to the size of soxhelt extractor. Prepared thimble should be placed in side soxhelt extractor,as not disturbing the folw of solvent

vapour up to the condenser and the flow of condensed solvent down to the thimble.

Size of the sample is very important, because smaller in size increases the extraction efficiency.

Anhydrous sodium sulphate was mixed with avocado sample to reduce the moisture in the sample.

Moisture removal is very important because fat extraction is not efficient with moisture.

The moisture removal also increases the penetration efficiency of the solvent into the tissues.

Refluxing was done for about 5 hours assuming that all the fat has been extracted to the solvent.

Usually, petroleum ether is colourless and it turns in to yellow colour due to extaction of fat.

After the extraction, the flask and its contents were kept in the ovenin 105 ℃ for 15-20 minutes.

Usually avocado contains high amount of chlorophyll, so it can be affected the result. With the extraction of fat, chlorophyll also can be extracted to the solvent.

According to the data bases total fat content of avocado is 22.8g / 100g . So free fat content should be less than that amount. And determined value of free fat is 9.02 %.

Conclusion :

The percentage of free fat content of the avocado sample on wet basis = 9.02 %

Determination of Total fat content of Avocado

Materials :

Beakers

Mojonnier flasks

Weighing Scale

Hot water bath

Chemicals :

Conc. HCl

Petroleum ether

Diethyl ether

95 % Ethyl alcohol

Procedure :

Dried powdered avocado sample was taken and 2g of the sample was added to a 100ml

beaker. A HCl solution was prepared by mixing 25ml of Conc. HCl and 11ml of distilled water. Then

10ml of that solution and 2ml of 95% ethyl alcohol were added to the beaker which containing the

avocado sample.

The contents were mixed thoroughly and the beaker was placed on a water bath (70-80 oC)

and the contents were stirred for about 30-40 minutes frequently.

After that the beaker was removed from the water bath and it was cooled until it obtains the

room temperature. Then 10ml of ethanol was added to it and the mixture was transferred in to the

Mojonnier flask. The beaker was washed with 25ml of Diethyl ether in three portions and that

solution was also added to the flask. The stopper was fixed to the flask and it was shaken for 1

minute.

Then 25ml of pet ether was added to the flask and it was shaken again for 1 minute. The

flask was allowed to stand until the upper ether layer is clear. The upper ether layer was transferred

to a clean, dried and previously weighed beaker. Then the beaker was dried in a water bath at 80oC

until a constant weight was obtained.

Data :

Sample No. Weight of the avocado

sample / g

Weight of the empty

beaker / g

Weight of the beaker and

Fat / g

12.0066

44.64 45.67

22.0163

107.06 108.08

32.0098

110.41 111.45

Calculation :

Percentage of Total fat = Weight of fat x 100%

Weight of the sample

= m2 - m1 x 100%

Weight of the sample

m1 = Weight of the beaker

m2 = Weight of the beaker + fat

Determination of total fat percentage in dry basis

Sample No. 1

Percentage of Total fat of avocado sample = 45.67 – 44.64 x 100%

2.0066

= 51.33 %

Sample No. 2


2.0163

= 50.69%

Sample No. 3


2.0098

= 51.89 %

Average value of the percentage of total fat = ( 51.33 + 50.69 + 51.89 ) %

content of the avocado sample (on dry basis) 3

= 51.30 %

Determination of free fat percentage in wet basis

Average % of moisture content in avocado = 75.31 %

Percentage of nutrient on wet basis = Percentage on dry basis x (100 - % of moisture)

100

Percentage of Total fat on wet basis = 51.30 x (100 – 75.31)

100

= 12.67 %

Percentage of total fat content of the avocado sample on wet basis is 12.67%.

Discussion :

In the determination of total fat content of avocado, Mojonnier method was used.

Here fat is extracted with a mixture of diethyl ether and pet ether which are used as extracting solvents in a majonnier flask.

For this experiment also, dried sample was used. Then first total fat amount is determined on dry basis and then it was converted to wet basis.

Size of the sample is very important, because smaller in size increases the extraction efficiency.

As the total fat both free fat and bound fat is considered. Here bound lipids can be made free by dissolving the sample in polar solvents. Dissolution of sample is achieved by acid. Sample is placed in a water bath and fat seperates as a layer on the top of the solution mixture. Seperated fat can be extracted by shaking at least 3 times with mixure of diethyl ether and pet ether.

After the extraction, the flask and its contents were kept in the oven in 105 ℃ for 5-10 minutes.

The observed value as total fat content of avocado sample is 12.76 % on wet basis. But according to the data bases there are few complications. Because in many sources it gives different values. But for the comparison here I used data bases released agriculture department of sri lanka. It indicates that total fat amount is 22.8 g / 100 g. But It can varied according to the variety.

According to the details gained from kananwila research center, total fat content in order to variety is as follows.

Name of the variety Percentage of total fat

Booth 7 7 – 13 %Pollock 4 – 8 %Fuerte 18 – 26 %

Tower 2 18 – 26 %Simmonds 3.5 – 5 %

For this experiment , I used Booth 7 variety, So it s recommended total fat amount is 7 – 13 %. Here I determined fat percentage as 12.76 %. So it is within the range.

There can be occurred some experimental errors and instrumental errors. When measuring the weights of the samples and the beakers instrumental errors can occur.

When transferring the diethyl ether and petroleum ether layers errors can occur. It’s difficult

to transfer the ether layers to the beaker until the very last drop. Residues also can be transferred to

the beaker in some occasions.

Conclusion :

Percentage of Total fat content of the avocado sample on wet basis is 12.76 %.

Blank Determination of Protein content

Materials :

Kjeldhal digestion kit

Titration flasks

Weighing balance

Burette

Chemicals :

4% Boric acid solution

Sodium sulphate solution

Distilled water

0.02M Standard HCl solution

Kjeldhal catalyst tablets

Indicators - Methyl red, Methylene Blue

Procedure :

Dried powdered avocado sample was taken and 0.1g of the sample was measured to

a tissue paper (1 inch x 1 inch) and it was transferred to the Kjeldhal digestion flask. One

Kjeldhal tablet and 2 ml of Conc. H2SO4 were also added to the flask.

Then the flask was connected to the fume trap and it was attached to the pump. The

sample was digested until a clear solution without blank particles is obtained. A blank

digestion was carried out too.

A small titration flask was taken and 5ml of 4% boric acid solution and 3 drops of

Kjeldhal indicator were added to it. This indicator was prepared by mixing two parts of 2%

alcoholic methyl red solution with one part of 0.2% alcoholic methylene blue solution.

Then, the digested sample was dissolved with a minimum amount of Ammonia free

distilled water and transferred to a semi micro Kjeldhal apparatus, which has been

previously conditioned by passing steam through it for several minutes slowly. After that, 8

ml of NaoH solutin prepared by dissolving 50g of NaOH pellets and 8g of sodium

thiosulphate in 100ml of distilled water was added to the flask.

Then the titration flask which containing 4% boric acid and the Kjeldhal indicator was

kept at the end of the digestion apparatus to trap the ammonia liberated. Steam was passed

through the flask until about 15ml of distillate is received. The solution which was collected

in the titration flask was titrated with a 0.02M Standard HCl solution. A blank distillation was

carried out too.

Data

Sample Number Weight of the sample / g Sample titre / ml( Required 0.02M Hcl volume

for titration)1 0.1001 3.60

2 0.1026 3.80

3 0.1008 3.60

Calculation

Calculation of crude protein content in dry basis

Nitrogen % = (Sample titre – Blank titre)×Molarity of Hcl×14×100

Weig h t of t he sample taken×1000

Protein = Nitrogen % × 6.25

sample 1

Nitrogen % in avocado sample 1 = (3.80 – o .oo)×0.02×14×100

0.1026×1000 = 1.04 %

Protein % in avocado sample 1 = 1.04 % × 6.25 = 6.5 %

Sample 2

Nitrogen % in avocado sample 2 = (3.80 – o .oo)×0.02×14×100

0.1001×1000 = 1.06 g Protein % = 1.06% × 6.25

= 6.625 %

Sample 3

Nitrogen % in avocado sample 3 = (3.60 – o . oo)×0.02×14×100

0.1008×1000 = 1.00 %

Protein % in avocado sample 3 = 1.00%× 6.25 = 6.25 %

Average % of crude Protein of avocado (dry basis) = 6.5 + 6.625 + 6.25 % 3

= 6.46 %

Calculation of crude protein content in wet basis

Average % of moisture content in avocado = 75.31 %

% of protein on wet basis = (percentage ondry basis )×(100−moisture )

100

% of crude Protein of avocado on wet basis = 6.46×(100 – 75.31)

100 = 1.59 %

Discussion

Here crude protein percentage of avocado was determined using kjeldhal method. Usually in food stuff, inorganic N content is negligible compared with organic nitrogen. Therefore only organic N is determined in the avocado sample.

There are three steps in kjeldhal method

Digestion Distillation Titration

Digestion

For the digestion, homogenized sample was used and it was digested in strong sulfuric acid in a heating unit at 340℃, in the presence of a catalyst(Cu/ Se/ Hg) which helps in the conversion of the organic nitrogen to ammonia and finally it is converted to (NH4)2SO4 .

K2SO4 or Na2SO4 are added as salts into the sample to increase the reaction mixture upto 390℃.

During digestion below oxidations and reduction are occurred.N NH3

NH3 + H2SO4 (NH4)2SO4 C CO2

S SO2

H & O H2O

Here we used a catalyst to increase the reaction rate. As catalyst we can use copper Sulphate with TiO2 or selenium or mercury.Hg as a catalyst, increase the reaction rate quickly, takes less time But the problem is it can be hazard effects due to toxic compounds. Se as a catalyst, indicate low reaction rate. Copper Sulphate with TiO2 is much safer but it takes long time.Here Hg is used based on the time factor. These catalysts are found as tablets.

Reaction which occurs during digestion,Organic N + H2SO4 (NH4)2SO4 + H2O + CO2 + By products

Electrical digestion grid was used for the digestion and cotton wool was used to cover all the places where toxic gas can be released.When weighing the samples, 1” x 1” tissue paper pieces were used, because in there we measuring minute amounts of samples, so there is an ability to remain some amount of

sample on the balance and also it’s easy to transfer sample in to kjeldhal flask without remaining the sample on the walls.

Analytical balance was used to measure the samples to minimize the measuring errors.

Digestion was carried out until a clear solution was observed.

Distillation

The second step is the estimation of generated ammonia produced by neutralizing the digest with alkali and trap NH3 in 4 % Boric acid.

Although it is necessary to add NaOH only, Na2S2O3 was mixed with NaOH pellets. Because if we use Hg as catalyst it forms a complex with NH3 . To break this complex we added Na2S2O3.

When dissolving the NaOH pellets with Na2S2O3 in water a water bath was used to prevent damages due to generation of heat.

The liberated NH3 moves out of the digestion flask and into the receiving flask - which contains an excess of 4% H3BO3.

At the low pH, NH3 gas is converted into the NH4+, and simultaneously converts the boric

acid to the borate ion.

Methyl Red + Methyl Blue mixture is used as the indicater here. When Indicator mix with H3BO3 it gives pink color. When it reacts with NH3 it gives green colour.

(NH4)2SO4 + 2 NaOH 2NH3 + 2H2O + Na2SO4

NH3 + H3BO3 (boric acid) NH4+ + H2BO3

- (borate ion)

Titration

Using a back titration with the boric acid in NH4+ using .02M HCl , produced NH3 amount

was determined. Colour change was green to pink. Then concentration of Hydrogen ions required to reach the end point is equivalent to the concentration of Nitrogen that was in the original avocado sample.

H2BO3- + H+ H3BO3

For the calculation, 6.25 was used as the conversion factor.

According to the data bases protein content of avocado is 1.7g / 100g. But through this practical, protein content was determined as 1.59 g / 100g. So there is a difference in standard protein content value and the observed value.

There can be determinate or systematic errors like instrumental errors, personal errors, and experimental errors.As an instrumental error , measuring the weight can be mentioned.As some experimental errors, some amount of NH3 Can be evaporated when alkaline mixture is added, All the protein may not be completely digested and some amount of NH3 Can be trapped in side the condenser.As Personal errors , Errors which occurs during taking the pipette and burette readings can be mentioned.

According to the environment conditions (soil, humidity, water level in soil etc.) where avocado plant was grown, protein content can be varied.

Conclusion

Precentage of crude Protein of avocado on wet basis is 1.59 %.

Determination of crude Fiber content of Avocado.

Materials :

1 liter conical flask

Air condenser

Beakers

Desiccator

Weighing balance

Litmus paper

Chemicals :

Dil, Sulphuric acid

Dil. Sodium hydroxide

Alcohol

Diethyl ether

Procedure :

Dried powdered avocado sample was taken and 3g of the sample was added to a 1

liter conical flask. Then 200ml of boiling 1.25% Sulphuric acid was added to the flask and the

air condenser was fixed to the flask.

Then the mixture was boiled for 30 minutes. While boiling the mixture, boiling water

was added to the flask whenever necessary to maintain the volume at a constant level.

While boiling the flask was swirled occasionally to remove solids from adhering to the sides

of the flask.

The hot solution was decanted through a Buchner funnel fitted with a piece of silk

cloth. The flask was rinsed with boiling water and the entire residue was transferred to the

Buchner funnel and filtered. The residue remaining on the funnel was rinsed with boiling

water until it is free from acid. The acidity was checked using blue litmus papers.

Then using 200ml of near boiling 1.25% NaOH solution, the residue was carefully

transferred to 1 liter flask from the silk cloth. The mixture was brought to boil as quickly as

possible and the gentle ebullition was maintained for 30 minutes. Boiling water was added

whenever necessary to maintain the volume.

The hot solution was decanted through a Buchner funnel fitted with a previously

weighted ash less filter paper. The entire residue was transferred quantitatively from the

flask to the Buchner funnel. Then it was washed with 1% HCl until the filtrate was free from

alkali, followed by distilled water, 15ml of alcohol and 10ml of diethyl ether.

A crucible was taken and it was cleaned and dried well. The weight of the crucible

was measured and the ash less filter paper was transferred to the crucible with the residue.

It was dried in an oven at 105oC until a constant weight was observed. After drying,

the weight was measured and then it was transferred to the muffle furnace and was

incinerated at 550 oC. The weight was measured after cooling the crucible using the

desiccator.

Data :

Sample 1 Sample 2 Sample 3

Weight of dried ash less filter paper / g 0.3667 0.3748 0.3623

Weight of dried empty Crucible /g 14.1268 14.9857 15.0126

Weight of dried sample / g 3.0200 3.0146 3.0146

Weight of the crucible + filter paper + residue after drying

in the oven / g

15.3490 15.6965 15.5298

Weigh of Crucible + ash after incineration /g 14.3230 15.2915 15.9792

Calculation

Determination fibre in dry basis

Sample 1

Weight of Crucible + ash + fibre residue = 15.3490 - 0.3667 g

= 14.9823 g

Weight of Crucible + ash = 14.3230 g

Percentage of fibre (dry basis) = Loss∈weight onincineration

Weight of the sample beforedefatting x100

= (14.9823 – 14.3230) x 100 3.0200

= 21.83 %

Sample 2

Weight of Crucible + ash + fibre residue = 15.6965 - 0.3748 g

= 15.3217 g

Weight of Crucible + ash = 15.2915 g

Percentage of fibre (dry basis) = Loss in weight on incineration x 100

Weight of the sample before defatting

= (15.3217 – 15.2915) x 100 3.0146

= 22.84 %

Sample 3

Weigh of Crucible + ash + fibre residue = 15.5298 - 0.3623 g

= 15.1675 g

Weigh of Crucible + ash = 15.8792 g

Percentage of fibre (dry basis) = Loss in weight on incineration x 100

Weight of the sample before defatting

= (15.8792– 15.1675) x 100 3.0146

= 23.61 %

Average Percentage of fibre content of avocado in dry basis = 21.83 + 22.84 +23.61

3

= 22.76%

Determination of fibre in wet basis


Percentage of nutrient on wet basis =Percentage on dry basis x (100 - % of moisture)

100

Percentage of fibre on wet basis = 22.76 x (100 – 75.31 )

100

= 5.62 %

Discussion

Mainly there are five steps in determination of crude fibre.

1. Defattering2. Acid digestion3. Alkaline digesion4. Dry and weigh residue5. Ash and weigh residue

1. Defattering

Normally defatting is done only for food which contains more than 1 % of fat. Therefore its necessary to analyze fat content before analyze fibre content. In avocado fat content is obtained as 12.76 % so fat content is more than 1% therefore defatting step was done using petroleum ether.

2. Acid digestionDuring acid digestion, sample was boiled with dil. H2SO4 for 30 min. Then protein

compounds can be eliminated by digestion.

3. Alkaline digestionDuring alkaline digestion, sample was boiled with dil. NaOH for 30 min. Then carbohydrate compounds can be eliminated by digestion.

4. Dry and weigh residueDigested sample was kept in oven until it removes moisture completely. Then

Residue contains only ash and fibre.

5. Ash and weigh residueSample was Incinerate at 500℃. Then ash in the sample is eliminated.

For this experiment also, dried sample was used. Then first total fat amount is determined on dry basis and then it was converted to wet basis.

In the digestion process hot handling is important continuously. The rate of heating should be gently boiled. Filtering should be done as soon as possible since late filtration generally results in lower results.

To reduce evaporation losses during boiling the reflux condenser is used. But in using reflux condenser it’s difficult to shake the sample therefore we used an air condenser.

In digestion we maintained the volume of the solution by adding hot water due to minimize concentration changes.

For the filtration after digestion with dil. H2SO4, piece of cloth was used. It is very suitable because fibre can comes out if we use a filter paper.

Litmus papers were used to check whether residue is acidic or basic.

In digestion except fiber others are dissolve in sulfuric acid and NaOH . Hemicelluloses get dissolve in dilute alkali while pectin and hydrocolloids dissolve in hot water. Protein is denatured and lost in strong acid treatment. But mineral matter do not get dissolve in above treatments. Due to this these remain with insoluble fiber matters. To avoid this error ash content is determined and deducts the amount of ash from the fiber.

Finally filtrate was washed with alcohol and diethyl ether to eliminate chlorophyll like pigments which may present in the sample.

In final filtration ash less filter paper must be used, otherwise fibers of the filter paper may added to the fiber content of the sample. It can give 97 % accuracy.

According to the data bases fibre content of avocado is 6.17g / 100g . But through this practical, fibre content was determined as 5.62 / 100g. So there is a difference in standard moisture content value and the observed value.

According to the environment (soil, humidity, water level in soil etc.) content it can be varied. There can be determinate or systematic errors like experimental errors and instrumental error like measuring the weight.All the proteins, carbohydrates may not be digested and there can be some remained part. It also can be affected for the final result. As well as avocado is a highly fat contained fruit. So defatting may not be 100% successful.

So these can be reasoned for the difference of standard value and determined value.

Determination of ash content in avocado sample

Materials :

Muffle furnace Crucibles Weighing balance Desiccator

Tongs

Procedure :

About 3 g of dried avocado sample was weighed into a clean dry pre weighed crucible. Then the sample was ignited slowly over a flame until no more fumes were evolved.The dish was transferred to muffle furnace until it was free of black carbon particles and turn into white in color. Dish was removed carefully and allowed to cool in a desiccator. It was weighed ofter taking out from desiccator and Process of ashing, cooling and weighing was repeated till no further loss in weight was indicated.Same procedure was done to three samples of dried avocado .

Data :

Sample No.

Weight of the empty crucible /g

(m0)

Weight of the Sample /g

Weight of the Sample + crucible before

ashing /g (m1)

Weight of the Ash + Crucible/g ( m2)

1 75.4590 3.0130 78.472 75.6473

2 77.3435 3.0044 80.3479 77.5361

3 75. 6728 3.0072 78.6800 75.8650

Calculation

Ash % m/m = weight of ash

Weigh t of t hesample

Ash % m/m = m2 – m0m1−m0

mo = Weight of empty crucible m1 = Weight of empty crucible + sample before ashingm2 = Weight of empty crucible + ash

Determination of total ash content ( Dry basis)

Sample 1

Ash percentage for Avocado sample 1 (m/m) = 75.6473−75.459078.472−75.4590 × 100 %

= 6.25 %Sample 2


= 6.41 %

Sample 3


= 6.39 %

Average Ash percentage for Avocado sample =6.25+6.41+6.39

3

= 6.35 %

Determination of total ash content in Wet basis


percentage of fibre on wet basis = (percentage on dry basis) × (100- moisture) 100

So the fibre percentage in dry basis = 6.35×(100−75.31)

100

= 1.57 %

Percentage of ash content of the avocado sample on wet basis is 1.57 %.

Detrmination of acid insoluble ash content in Avocado

Materials:

10% HCl acid Litmus paper Filter funnels Ash less filter paper Beakers Hot water

Procedure:

Ash residue of avocado samples was dissolved in 10% HCl and filtered through an ash less filter paper. The filtrate was washed with hot water until the filtrate was free from acid. The filter paper with containing the ash was carefully transferred into the porcelain dish and incinerated. The dish was transferred into the muffle furnace at 550oC and kept until got white or gray colour residue. Dish was cooled in a desiccator and weighed until a constant weight is obtained.

Data :

Sample No Weight of the empty crucible /g

Weight of the Sample + crucible before

ashing / g

Weight of the acid insoluble ash+ crucible

/ g

1 75.4590 78.4720 75.4626

2 77.3435 80.3479 77.3483

3 75.6728 78.6800 75.6785

Calculation

Acid insoluble ash percentage (m/m) = weight of acid insoluble ash X 100%

Weight of Sample

Sample 1

Acid insoluble ash percentage (m/m) for sample 1 = (75.4626– 75.4590) X 100% ( 78.4770 – 75.4590)

= 0.12%

Sample 2

Acid insoluble ash percentage (m/m) for sample 2 = (77.3483 – 77.3435) X 100% ( 80.3479 – 77.3435)

= 0.16 %

Sample 3

Acid insoluble ash percentage (m/m) for sample 3 = (75.6785 – 75.6728) X 100% ( 78.6800 – 75.6728)

= 0.19 %

Average Acid insoluble ash percentage (m/m) in avocado =( 0.12 + 0.16 + 0.19) % 3

= 0.156 %

Determination of total ash content ( Wet basis)


percentage of acid insoluble ash on wet basis = (percentage on dry basis) × (100- moisture) 100

So the acid insoluble ash percentage in wet basis = 0.156×(100−75.31)

100

= 0.039 %

Discussion

In determination of ash content of avocado, dry ashing method was used. It requires a muffle furnace capable of maintaining 550 °C. During dry ashing, water and volatiles are vaporized and organic compounds are oxidized via O2 in air into CO2, CO, and N-oxides.

Most minerals are converted to oxide, sulfates, phosphates, chlorides and silicates.

Usually crucibles are used which are prepared of Pt , Ni , Si,and porcelain. These crucibles can tolerate temperature up to 1200 ℃ and can store at higher temperature also. As well as they are easy to clean.

Sample was incinerated until it is free of black carbon particles and it is white in colour. Some inorganic matter (Fe, Se, Pb, Hg) could volatilized during ashing.

According to the data bases ash content of avocado is 1.04g / 100g . But through this practical, ash content was determined as 1.57 / 100g. So there is a difference in standard ash content value and the observed value.

Although sample was white in colour after ashing, All the organic matter may not be burnt away.

According to the environment conditions (soil, humidity, water level in soil etc.) where avocado tree was grown, ash content can be varied.

There can be determinate or systematic errors like experimental errors and instrumental error like measuring the weight.

Acid insoluble ash Refers to ash that is insoluble in acids such as sandy matter. It should be less than ash content. In this experiment 0.039 % of acid insoluble ash content was determined.

Conclusion

Percentage of ash content of the avocado sample on wet basis is 0.156 %

Percentage of acid insoluble ash content of the avocado sample on wet basis is 0.039 %.

Avocado Proximate analysis

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