Journal of the Science of Food and Agriculture J Sci Food Agric 80:1903±1908 (online: 2000)

Dietary fibre content of table olives processedunder different European styles: study ofphysico-chemical characteristicsAna Jimenez, Rocio Rodrıguez, Ignacio Fernandez-Caro, Rafael Guillen,Juan Fernandez-Bolanos and Antonia Heredia*Departamento de Biotecnologıa de los Alimentos, Instituto de la Grasa (Consejo Superior de Investigaciones Cientificas), Apdo 1078,41012-Sevilla, Spain

(Rec

* CoInvesE-maCont

# 2

Abstract: Some European varieties of olive fruit (Douro, Hojiblanca, Cassanese, Conservolia,

Taggiasca, and Thasos), processed under different conditions (black oxidised, fermented in brine or

dried by different methods) were analysed, their contents of moisture, fat and dietary ®bre being

quanti®ed. The percentages of moisture and fat were very different between varieties due to the

different processing conditions, although differences between samples of the same variety were much

less. The content of dietary ®bre was around 12% of the fresh weight, although in dried samples this

percentage increased to around 20%. Some physico-chemical characteristics (water holding capacity,

cation exchange capacity, and ion retention capacity) were measured. The water holding capacities

were related to moisture content, dry samples having the lowest values. Processed olives had very low

cation exchange capacity in comparison to other vegetables, exhibiting the same relationship between

this characteristic and moisture content. Olive ®bre retained more iron than calcium under the assay

conditions.

# 2000 Society of Chemical Industry

Keywords: table olives; European varieties; dietary ®bre; physico-chemical characteristics; nutritional value

INTRODUCTIONDietary ®bre has been traditionally de®ned as the total

polysaccharide and lignin of the diet that is not

digested by endogenous secretions of the digestive

tract.1 Cell walls of fruits, vegetables, pulses and

cereals make up the most of dietary ®bre intake,2 since

the most important ®bre components are also struc-

tural components of the cell walls.3,4

The main objectives of current research on this

subject have been to ®nd a universal concept of dietary

®bre and to establish accurate methodologies for its

determination. Also, knowledge of the physiological

effects of this component of foods in humans is of great

interest. The physiological effects are related to

physico-chemical and functional properties of dietary

®bre, eg its degradation by bacteria, viscosity, water

holding capacity, bile acid retention, mineral reten-

tion, and cation exchange capacity. It is widely known

that dietary ®bres of different origins behave differ-

ently during their transit of the gastrointestinal tract,

depending on their physico-chemical characteristics5

and on the processing that the foods undergo.6

Olives are among the fruits with an appreciable

content of dietary ®bre.7 Their consumption as table

eived 28 February 2000; revised version received 17 May 2000; acce

rrespondence to: Antonia Heredia, Departamento de Biotecnologıatigaciones Cientificas) Apdo 1078, 41012-Sevilla Spainil: ahmoreno@cica.esract/grant sponsor: EU; contract/grant number: FAIR-CT97-3053

000 Society of Chemical Industry. J Sci Food Agric 0022±5142/2

olives is very important in the Mediterranean zone (the

main producer countries) and in other non-producer

countries because of their favourable organoleptic

characteristics.8 Studies of olive dietary ®bre have

been carried out for several olive varieties, Hojiblan-

ca,9,10 Manzanilla and Gordal.11±13 Olive cell walls

have been also characterised14 as well as polysacchar-

ide modi®cations due to processing.14±19 The aim of

this work has been the determination of dietary ®bre

content of several European olive varieties, with

particular emphasis on the effect of ripening, proces-

sing and storage. Some physico-chemical characteris-

tics have also been studied in order to increase the

value of this fruit from a nutritional point of view.

EXPERIMENTALOlive fruit samplesSix varieties of processed olives fruits (Olea europaea L)

from different European countries have been used. In

Table 1 the different conditions of ripening, proces-

sing and/or storage are summarized. Samples were

provided by MacËarico Lda (Douro var), Agro-Sevilla

Aceitunas SCA (Hojiblanca var), Brogna Olei®cio

pted 31 May 2000)

de los Alimentos, Instituto de la Grasa (Conseyo Superior de

000/$30.00 1903

Table 1. Description of the samples studied in this work

Sample Variety Processing Factor studied

D4 Douro (PT) Black oxidised Stage of ripening Green fruit

D8 Cherry fruit

D12 Black fruit

H4 Hojiblanca (ES) Black oxidised Stage of ripening Green fruit

H8 Cherry fruit

Ca2 Cassanase (IT) Oven dried Processing Traditional (boiling, debittering, and oven-drying)

Ca3 Industrial (debittering and oven-drying)

C2 Conservolia (GR) Fermented in brine Time of storage In brine

C3 After 6 months

T3a Taggiasca (IT) Fermented in brine Conditions of storage In brine

T3b In acidi®ed brine

T3c In water prior to brine

T3d In water prior to acidi®ed brine

Th2 Thasos (GR) Dry salted Conditions and time of storage Dry salted

Th3 Dry salted, 4 months stored under nitrogen

Th4 Dry salted, 4 months stored under sorbic acid

Th5 Dry salted, 4 months stored under vacuum

Th6 Dry salted, 4 months stored under air

A JimeÂnez et al

Gabro SNC (Cassanese var), Institute of Technology

of Agricultural Products (Thasos var), DE Georgoudis

Co (Conservolia var), and Fratelli Carli SpA

(Taggiasca var).

Moisture determinationOlives were depitted, and the ¯esh homogenized.

Three aliquots of each sample (5g) were weighed into

capsules to within 0.1mg and dried under vacuum

(about 25mmHg) at 60±70°C until constant weight.

Fat extractionFat was determined in triplicate by Soxhlet extraction

with hexane for 2h from dried samples. The solvent

was removed in a rotary evaporator at 40°C, and the

residual oil dried.

Dietary fibre determinationDry defatted pulp in triplicate was dispersed in a buffer

solution of MES/TRIS as described by Lee et al,20 and

sequentially treated with the enzymes: (a) a-amylase

(100°C, 15min); (b) protease (60°C, 30min); (c)

amyloglucosidase (60°C, 30min). After digestion, hot

(60°C) ethanol was added to precipitate the soluble

®bre. Ash and protein corrections were made at this

step.

Protein determinationThe proteins were estimated by the micro-Kjeldahl

method on the residue of one of the replicates after

®bre determination. Kjeldahl nitrogen was converted

to protein using the factor 6.25.

Ash determinationAnother replicate of ®bre determination was reduced

to white ashes in an oven at 450°C overnight.

1904

Isolation of alcohol insoluble residue (AIR)Duplicate 50g samples of the Douro, Hojiblanca,

Cassanese, Conservolia, Taggiasca, and Thasos vari-

eties were homogenised at top speed in an Ultra-

Turrax T-25 with four volumes of 96% ethanol. After

centrifugation (1300g, 10min), samples were washed

again with 80% ethanol. The pellets were resuspended

several times in acetone until supernatants were

colourless.21 The dried ®nal residue (AIR) was used

for determination of the physico-chemical characteris-

tics of ®bre.

Study of water retentionThe water holding capacity (WHC) study was based

on the method of McConnell et al. 22 Samples (250mg

(�4)) of AIR were suspended in 15ml water. After

24h of stirring at room temperature, the suspension

was centrifuged at 14000g for 1h. The supernatant

was discarded and an aliquot of the pellet was weighed

into a pre-weighed tube and freeze-dried. The

difference in weight expressed as ml watergÿ1 AIR

was considered as the WHC.

Study of ion exchange capacityThe cation exchange capacity (CEC) was adapted

from Moorman et al. 23 Samples (500mg of AIR (�4))

were suspended in 25ml of 2N hydrochloric acid. After

24h of continuous stirring, the suspension was

centrifuged for 15min at 2500g. The residue was

washed several times with distilled water until the pH

of the supernatant was above 4. The acidic residue was

suspended in 25ml of 0.3M sodium chloride (�3)

together with a blank with distilled water, and after

stirring and centrifugation as above, the supernatant

was titrated with 0.01 N sodium hydroxide. The ®rst

J Sci Food Agric 80:1903±1908 (online: 2000)

Table 2. Moisture and fat contents expressedon fresh weight basis, of the different samplesanalysed. Different letters within the samevariety indicate significant differences

Sample a Moisture (%) Fat (%)

D4 9.6 a 78.9 a

D8 13.9 b 77.1 a

D12 13.0 b 78.4 a

H4 10.2 a 73.2 a

H8 12.8 b 69.7 b

Ca2 51.5 a 20.5 a

Ca3 27.5 b 48.1 b

C2 23.5 a 56.3 a

C3 23.2 a 63.1 b

T3a 41.7 ab 47.1 a

T3b 44.5 ab 43.7 b

T3c 40.5 ab 48.1 a

T3d 38.8 b 48.8 a

Table olive dietary ®bre: physico-chemical characteristics

wash with distilled water of this blank was also titrated.

CEC was expressed as meq gÿ1 AIR.

Study of cation retentionThe cations assayed for ion retention capacity (IRC)

are Fe(II) and Ca(II).24 Samples (100 or 200mg) of

AIR (for Fe(II) and Ca(II) determination, respec-

tively) (�2) plus a blank with distilled water were

suspended in 20ml of 75ppm cation solution. After 3h

stirring at room temperature, the suspension was

centrifuged for 15min at 2500g and the concentration

of cation was measured in the supernatant by atomic

absorption spectrophotometry. The IRC was ex-

pressed as mggÿ1 AIR.

Statistical analysisThe data were statistically analysed through their

variance. Means were compared by Duncan's multiple

range test (p<0.05).

Th2 38.8 a 27.1 a

Th3 33.5 b 21.0 b

Th4 34.0 b 20.4 b

Th5 34.3 b 19.9 b

Th6 33.9 b 19.8 b

a Sample descriptions are listed in Table 1.

RESULTS AND DISCUSSIONDietary ®bre has been isolated from each sample

provided by the different companies. Within each

group of samples one or two properties are going to be

discussed, as shown in Table 1. Douro (D4, D8, D12)

and Hojiblanca (H4, H8) olives were harvested at

different stages of ripening, the samples of each variety

undergoing the same processing. The property com-

pared in the Cassanese variety (Ca2, Ca3) was the

method of processing, and in Conservolia (C2, C3)

the storage time. Taggiasca (T3a, T3b, T3c, T3d) and

Thasos (Th2, Th3, Th4, Th5, Th6) were stored under

different conditions and the latter variety were

analysed after a storage period. The physico-chemical

characteristics of the isolated dietary ®bre have been

studied.

Moisture and fat contentsAs a consequence of the different kinds of processing

the moisture and fat content in the samples varied

greatly (Table 2). The highest moisture level was

found in olives that underwent an alkaline treatment

(Douro and Hojiblanca), a process which favours the

hydration of the fruits by disrupting cuticular waxes.7

In these ®ve samples, 70±80% of the fresh weight was

water. Although Douro olives were harvested at

different ripening stages, there were no signi®cant

differences in moisture content, unlike the ®ndings in

Hojiblanca where cherry fruits (H8) had lower water

and higher fat contents than green fruits (H4), as

previously observed.25

An intermediate moisture content was found in

brined olives without alkaline treatment, from Con-

servolia and Taggiasca varieties (40±60%). In the case

of Conservolia, there were signi®cant increases in

moisture content after 6 months of storage, showing

the effect of the slow osmotic process through the olive

cuticle during brining. Fat content remained un-

changed. Dried olives (Cassanese and Thasos vari-

J Sci Food Agric 80:1903±1908 (online: 2000)

eties) had a moisture content of around 20% and a fat

content of 30±50%, depending on the samples.

Two interesting facts are worth remarking on at this

point. There were signi®cant differences between the

traditional and the industrial processings of Cassanese

olives. Boiling treatment during the traditional process

involved a more intense drying effect on the fruits. In

Thasos, the storage period of the dry salted olives

caused a decrease in the moisture and fat contents of

olives, although the different storage conditions had

no effect.

Dietary fibre contentResults obtained on the quanti®cation of dietary ®bre

are presented in Table 3. In general, the dietary ®bre

contents of the samples were 10±15% (approx). Only

Ca3, C2, and Th3±Th6 were around 20%. In Douro,

®bre content decreased signi®cantly with ripening,

unlike previously reported results in Hojiblanca.25 In

Cassanese processing, the boiling step of Ca2 may

initiate a loss of polysaccharides and other compo-

nents, thus leading to a signi®cant decrease in dietary

®bre. A similar decrease was quanti®ed in Conservolia

variety. In this case the loss of dietary ®bre may have

been due to a longer period in brine (6 months of

storage). This decrease would be caused by a more

intense solublisation of polysaccharides into brine and

also to higher modi®cations due to chemical condi-

tions of storage. The different storage conditions of

Taggiasca variety had a very minor effect on ®bre

content, the only signi®cant quantitative differences

being between samples T3a and T3c. Again, in Thasos

1905

Table 3. Dietary fibre contents, expressedon fresh weight basis, of the differentsamples analysed. Different letters withinthe same variety indicate significant differ-ences

Sample a Dietary ®bre (%)

D4 12.3 a

D8 10.9 b

D12 11.2 b

H4 11.4 a

H8 14.1 b

Ca2 9.6 a

Ca3 19.1 b

C2 16.3 a

C3 9.7 b

T3a 13.6 a

T3b 12.1 ab

T3c 11.4 b

T3d 12.0 ab

Th2 11.9 a

Th3 17.5 b

Th4 19.0 b

Th5 19.1 b

Th6 21.1 c

a Sample descriptions are listed in Table 1.

Table 4. Water holding capacity (WHC), cation exchange capacity (CEC),and ion retention capacity (IRC) of the samples studied in this work. Differentletters within the same variety indicate significant differences

Sample a

WHC

(mlgÿ1 AIR)

CEC

(meqgÿ1 AIR)

IRC (mggÿ1 AIR)

Fe(II) Ca(II)

D4 12.8 a 0.10 a 13.7 a 6.9 a

D8 10.3 b 0.10 ab 14.1 b 6.1 b

D12 10.0 b 0.11 b 13.7 a 6.9 a

H4 10.3 a 0.10 a 15.4 a 6.5 a

H8 10.4 a 0.11 a 15.3 a 5.7 b

Ca2 7.3 a 0.05 a 7.3 a 2.9 a

Ca3 8.3 b 0.05 b 9.5 b 4.0 b

C2 8.0 a 0.07 a 12.9 a 5.5 a

C3 7.1 a 0.05 a 7.4 b 3.4 b

T3a 8.8 a 0.08 a 8.9 a 5.1 a

T3b 7.6 b 0.07 b 8.8 ab 5.0 ab

T3c 7.3 c 0.07 b 9.2 a 4.8 b

T3d 7.0 c 0.06 c 8.5 b 4.2 c

Th2 7.1 a 0.05 a 4.7 a 2.4 a

Th3 7.5 a 0.04 ab 6.0 b 2.3 ab

Th4 7.1 a 0.02 c 6.5 c 2.2 bc

Th5 7.2 a 0.04 b 6.1 bc 2.1 c

Th6 7.0 a 0.04 ab 5.9 b 2.5 a

a Sample descriptions are listed in Table 1.

A JimeÂnez et al

variety, the period of storage had more signi®cant

effects than the storage conditions. The amount of

dietary ®bre increased due to a decrease in the

moisture and fat content in the stored samples.

Physico-chemical characteristic of dietary fibreResults obtained for water holding capacity (WHC),

cation exchange capacity (CEC) and ion retention

capacity (IRC) are presented in Table 4.

The effect of ripening was studied on Douro and

Hojiblanca varieties. Both varieties had the highest

values in all the measured parameters, and were very

similar for both Douro and Hojiblanca. WHC was

around 10ml gÿ1 AIR. In Douro this characteristic

showed a slight but signi®cant decrease as ripening

progressed. In Hojiblanca this property did not

change. CEC increased signi®cantly with ripening,

and was about 0.1meqgÿ1 AIR in both varieties. IRC

behaved differently depending on the cation. Iron

retention did not change signi®cantly in either variety,

in Douro being around 14mg gÿ1 AIR and in Hoji-

blanca around 15mg gÿ1 AIR. Calcium retention

decreased between green and cherry samples (D4

and D8) and also in Hojiblanca samples. In Douro the

black sample (D12) had a higher calcium retention,

similar to that of D4.

The effect of different processing conditions was

studied in Cassanese variety (Ca2 and Ca3), with

comparisons made between the traditional and in-

dustrial processing methods. All physico-chemical

characteristics increased signi®cantly with industrial

processing (Ca3).

1906

In Conservolia, the only characteristic affected by

storage was the retention capacity of Fe(II) and Ca(II),

which decreased after 6 months. The different storage

conditions in Taggiasca variety led to signi®cant

differences. T3a (direct brining) had the highest values

and T3d (in water prior to acidi®ed brining) the

lowest, showing the importance of the storage condi-

tions on the physico-chemical characteristics of dietary

®bre. Similarly in Thasos, all the characteristics except

for WHR showed signi®cant differences in most

samples. CEC was affected very clearly during storage

in sorbic acid (Th4), its capacity decreasing from

approx 0.4 to 0.22meqgÿ1 AIR. However, this sample

that retained the highest amount of Fe(II) (6.51meq

gÿ1 AIR), showed the different linking mechanism

between Fe(II) and other cations such as sodium or

protons.

It is interesting to note that samples which had

higher moisture percentages (Douro and Hojiblanca

varieties) also had higher values of the other charac-

teristics. As mentioned for moisture content, these

factors could be also related to the alkaline treatments

that Douro and Hojiblanca olives underwent. In this

processing, pectins suffer considerable deesteri®ca-

tion,15,17,18 yielding macromolecules more able to

interact with cations ionically or by forming coordina-

tion complexes.21 Samples with intermediate values of

moisture (Cassanese industrially processed, Conser-

volia, and Taggiasca) also had intermediate values in

WHC, CEC and IRC. Dry samples (Cassanese

traditionally processed and Thasos) had the lowest

values of the three characteristics. Drying processes

J Sci Food Agric 80:1903±1908 (online: 2000)

Table olive dietary ®bre: physico-chemical characteristics

affected the structure of ®bre to a signi®cant extent,

limiting its physico-chemical capacities. This was very

clear when comparing the traditional processing

method (Ca2) with the industrial one (Ca3) in

Cassanese. Working with the same variety and

ripening stage, traditional processing led to a drier

product than did the industrial processing, the former

having lower values of WHC, CEC, and IRC.

CONCLUSIONSIn comparison with other vegetable products, the

WHC and CEC values found in processed olives are

appreciable. WHC varies from approximately 23ml

gÿ1 dry defatted residue (DDR) of lettuce and carrot,

10±11ml gÿ1 DDR of tomato and Brussel sprout,

wheat bran approximately 5ml gÿ1 DDR, to 1±

2ml gÿ1 DDR of maize and potato.5,26 The range of

values for olives processed under different conditions

was 7±12ml gÿ1 AIR, values that are in the average

zone of the range reported for other vegetables. In

CEC, olives are not within the reported range for this

characteristic, which varies from 3.1meqgÿ1 DDR of

lettuce, 2.4meqgÿ1 DDR of carrot, 1.0meqgÿ1 DDR

of celery, to 0.2meqgÿ1 DDR of potato and wheat

bran.5 Most of the studied processed olives had

0.02±0.07meqgÿ1 AIR of CEC, and only alkali-

treated olives (Douro and Hojiblanca varieties), where

pectins have a low degree of esteri®cation, had

0.1meqgÿ1 AIR. These low values for CEC imply a

low retention capacity for iron and calcium, a property

that gives the ®bre an `antinutritional' value. The

present study on processed olives values these pro-

ducts highly because of their dietary ®bre content of

10±20% and for their physico-chemical characteris-

tics. These features, together with the high percentage

of olive oil present in these vegetable products

(20±50%), as well as their appreciable organoleptic

characteristics, make processed olives very healthy

vegetable products. This analytical evaluation is

supported by the increase that has taken place in the

international trade of processed olives, where Medi-

terranean countries are the main producers.

ACKNOWLEDGEMENTSWe want sincerely to thank Mr Gil MacËarico

(MacËarico Lda, Portugal), Mr Luis Rejano (Agro-

Sevilla Aceitunas, SCA, Spain), Mr Mauro di Brogna

(Olei®cio Gabro SNC, Italy), Dr Konstantinos Kat-

xaboxakis (Institute of Technology of Agricultural

Products, Greece), Mr Danielos Georgoudis (DE

Georgoudis Co, Greece), and Dr Mauro Amelio

(Fratelli Carli SpA, Italy) for the supply of samples.

This work was supported by EU Project OLITEXT

FAIR-CT97-3053.

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