J. Sci. Fd Agric. 1975, 26,207-213

Seasonal English Market Variations in the Composition of South African and Israeli Avocados

David Pearson

National College of Food Technology (Uniuersity of Reading), Weybridge, Surrey KT13 ODE (Manuscript received 4 June 1974 and accepted 28 August 1974)

Avocados imported from South Africa in the summer and from Israel in winter were examined over a 12-month period. The main changes over the seasons were a marked fall in the water content (South African from 78 to 50 %, Israeli from 79 to 67 %) with a concomitant increase in the amount of extracted oil (South African from 13 to 40%, Israeli from 11 to 23%). Apart from the oil, the amounts of protein, ranging from 1.2 to 2.4% (3.6-9.8 % on the dry basis), and ash (approxi- mately 1 %) are higher than in other fruits. Avocados contain relatively little carbohydrate and the amount of sugars varies according to factors such as the time of picking and treatment prior to the analysis. The total sugars seldom exceed 1 % and no sucrose was detected in any of the fruits examined. Oil is the major con- tributor to the energy value, which varies for all samples examined from 123 to 387 kcal per 100 g. As the fruit weight tends to show a seasonal fall the variation in the calorific value is not so great when calculated on a "typical half" which is the usual basis for dietary calculations. Formulae are presented for calculating the approximate calorific value from the oil content, and the oil figure from the water content.

1. Introduction

The increasing importance of the avocado (Persea americana) in the retail and catering trade in the United Kingdom can be gauged from the total tonnage imported in 1973 (over 5000 tons) compared with 1963 when the figure was less than 600 tons. Also imports were nearly 40% higher in 1973 than in 1972.' About 60 % comes from South Africa and Israel supplies most of the rest. As the fruit comes to maturity in the winter in the growing areas the two seasons are complementary, viz. South Africa from March to October and Israel from September to April. The commonest variety imported from both areas is the Fuerte with a bright green and smooth skin. Other varieties with a similar appearance are Edranol from South Africa and Ettinger from both countries. Israel also sends avocados of the Hass variety with a purplish black warty skin, and a larger and rounder (not pear-shaped) variety, Nabal, which has a smooth and bright green skin.

The fruits are picked when they are mature but still firm and they are then cooled to 5 "C and maintained at that temperature subsequently and during sea transportation. South Africa also uses air transport in the early part of her season. Avocados are size- graded and packed in containers containing 8-18 per tray.

207

D. Pearson

The intention of this study was to cover the composition of avocados sold at the major United Kingdom fruit and vegetable markets. Several workers 2-8 have published data following the examination of individual fruits and Stah19 in Florida and Appleman (in work recorded by Biale and Young") in California studied changes in composition of avocados partly in relation to maturity. There is no evidence however that there has been a previous study of the monthly changes in avocados imported into the United Kingdom from both Israel and South Africa and covering a full 12-month period. Data quoted for one sample by authorities such as McCance and Widdowson4 (e.g. water 81.3 %, fat 8.0 %) do not represent typical figures for the fruits sold in the United Kingdom over a 12-month period. Platt5 however does quote a range for the water content from 64 to 86 %.

203

2. Experimental

Edible matter After arrival at the laboratory the fruits were kept at room temperature until they were reasonably soft. The skin and seed were then removed carefully and the edible matter was calculated as a percentage of the whole fruit. Samplepreparation The separated flesh from several fruits was thoroughly comminuted and transferred to a large stoppered jar. Portions were immediately weighed out for the various analyses. Water was estimated by drying at 100 "C to constant weight.'l Oil content was determined on the dried flesh by extraction with light petroleum (bp 40"-60°).1' Protein (total nitrogenous matter) was estimated by the macro-Kjeldahl method12 and calculated using the factor N x 6.25. Ash was weighed after ignition of the sample at 600 OC.'l Fibre was estimated by the method officially prescribed for feeding stuffs.13 Acidity was determined by titration with dilute sodium hydroxide solution using phenolphthalein as indicator and calculated as citric acid. Total carbohydrate was calculated by difference. Sugars were determined by the Lane and Eynon methodlZ on a 20 w/v solution after clearing with the Carrez reagents. To check for the presence of sucrose the 20 % extract was hydrolysed with hydrochloric acid.13 Calorific value was calculated by the method prescribed in The Labelling of Food regulation^.^^ The results were also checked by burning the dried material in a bomb calorimeter. Potassium and sodium were both estimated using an EEL flame photometer on the solution of the ash in hydrochloric acid.15

3. Results and discussion

The monthly results obtained from the examination of South African and Israeli avocados from Covent Garden Market, London from April 1973 to April 1974 are given in Tables 1,2 and 3. As most diners only eat half an avocado at a time figures are also included for a "typical half", i.e. half of the edible flesh less stone and skin. These

Seasonal variations in composition of avocados 209

are useful in the preparation of diets and in obtaining meaningful comparisons of components such as the oil which, together with the weight, varies considerably over the season. All the samples examined were Fuerte avocados except for those imported from Israel in April 1973 and 1974 (at the end of the season). Of these the results found on Hass avocados seemed to correspond with the trends found in Fuertes, but the Nabal

Table 1. Changes in the composition of South African Fuerte avocados sampled from Covent Garden from April to October 1973 (analytical determinations made on edible portion only)

Date samples received 16.4.73 14.5.73 20.6.73 13.7.73 13.8.73 17.9.73 2.10.73 Range of weights (g) 246-300 251-289 324-393 246-302 218-307 145-282 154214 Mean weight (g) 268.1 268.6 358.6 276.5 266.7 202.8 180.7 Water (‘4 77.8 75.5 74.0 65.5 59.9 50.5 52.3 Oil (%) 13.0 15.8 18.5 25.4 31.3 40.0 39.1 Calorific value 141 160 184 251 304 387 376

Composition of dry matter Oil (%) 58.6 64.9 71.2 73.6 78.1 80.8 82.0 Protein (N x 6.25) (‘4 5.9 4.9 5.8 4.3 4.7 4.8 3.6 Ash ( %) 4.5 4.5 4.6 3.5 3.0 1.6 1.7 Fibre (%) 8.1 12.2 6.5 5.5 4.7 3.4 3.4 Acidity 1.4 0.85 0.92 0.29 0.25 0.20 0.34

Carbohydrate (‘4 21.5 12.6 11.0 12.8 9.2 9.2 9.0 Sodium (mg/100 g) 4 4 4 6 3 6 8 Potassium (%> 2.1 1.7 1.5 1.2 1 .o 0.70 0.75 Typical half Weight (g) 94 94 126 97 93 71 63 Water (g) 73.1 71.0 93.2 63.5 55.7 35.8 32.9

Oil (g) 12.2 14.9 23.3 24.6 29.1 28.4 25.0 Calorific value (cal>” 133 150 232 243 283 275 237

Potassium (mg) 442 400 491 388 363 248 223

(ca1/100 g>”

(as % citric acid)

Protein (g) 1.2 1.1 1.9 1.4 1.8 1.7 1.1

Sodium (mg) 1 1 1 2 1 2 3

a Estimated by method prescribed in The Labeiiing of Food Regulations 1970 (SI 1970 No. 400). Based on mean figure for edible matter of 70%.

avocados are quite different in weight and composition (Table 3) so they are excluded from the discussion which follows. Although the history and maturity of the fruits available at Covent Garden cannot be controlled in the same manner as with those examined in the growing a r e a ~ , ~ * l ~ the results should be of greater interest to the trade and consumers in the United Kingdom.

3.1. Weights of individual fruits and edible matter Both South African and Israeli avocados showed an early season increase in weight followed by a progressive decrease, covering an overall range from 130 to 393 g. In comparison Appleman reported a steady increase during the August-May period from about 70 to 200 g.l0 The proportion of edible matter in all fruits examined varied from 64 to 81 %. In view of the wide variation found and the subjective nature of the examination it was decided to use an average figure of 70% for calculations of the “typical half ”.

210 D. Pearson

Table 2. Changes in the composition of Israeli Fuerte avocados from November 1973 to March 1974 (analytical determinations made on edible portion only)

Date sample received Range of weights (g) Mean weight (9) Water ('4 Oil ('4 Calorific value (ca1/100 g>" Composition of dry matter Oil (%) Protein ('4 Fibre ('4 Acidity (as % citric acid) Carbohydrate ('4 Sodium (mg/lOO g) Potassium ('4 Typical harf Weight (g) Water (g) Protein (9)

Ash (%)

Oil (g) Calorific value (cals" . , Sodium (mg) Potassium (mg)

2.10.73

271.7 78.7 10.7

236-296

126

50.2 6.1 5.6 7.5 0.56

30.0 19 1.8

95 74.8

1.2 10.2

120 4

356

20.11.73 278-355 315.4 75.4 15.8

164

64.2 8.9 4.5 8.5 0.49

13.4 24

1.7

110 82.9 2.4

17.4 180

7 449

11.12.73

284.2 76.5 14.7

249-332

155

62.6 9.8 4.3 7.7 0.55

15.0 17 1.8

99 76.5 2.3

14.6 153

4 41 8

8.1.74 193-308 244.9 74.8 16.7

171

66.3 9.1 4.4 7.9 0.36

11.9 16 1.7

86 64.3 2.0

14.4 147

3 347

13.2.74 187-221 210.0 70.2 20.8

209

69.8 6.4 5.4 6.0 0.40

12.0 17 1.5

73.5 51.9

1.4 15.4

155 4

324

12.3.74 184-270 231.0 69.0 23.0

225

74.2 5.5 4.5 6.1 0.26 9.4

1.5 26

81 55.9

1.4 18.6

182 6

384

a Calculated by method prescribed in The Labelling of Food Regulations 1970 (Sl 1970 No. 400). Based on mean figure for edible matter of 70 %.

3.2. Water and oil

These figures show the most significant seasonal changes, but the sum of the percen- tages of water and oil for all the samples is fairly constant and of the order of 91. Over the season the water content of the South African samples fell from 78 to just over 50% with a concomitant increase in the oil figure from 13 to 40% (58.5 to 82.0% when calculated on the dry matter). The changes in the Israeli avocados were not so marked, uiz. water from 79 to 67 % with the oil rising from 11 to 23 % (50.2 to 74.2 % when calculated on the dry matter). In general the fall in the water content takes place more slowly in the early part of the season. These general trends correspond with the results reported on United States avocados, but Appleman found a higher range for water and lower figures for the oil. More generally it is apparent that end-of-season South African avocados contain more oil than those from other areas, e.g. Biale and Younglo quote 31.6% as the maximum for mature Californian varieties.

3.3. Protein Avocados contain more protein than other fruits. The average figure found for protein in the flesh is 1.7 %, which is slightly lower than that reported for Californian varieties. In the current work there is a tendency for the protein in the flesh to increase over the season, but when calculated on the dry basis there is a slight rise in the early months followed by a distinct fall.

Seasonal variations in composition of avocados 211

Table 3. Composition of Israeli avocados of different varieties

Variety Hass Nabal Fuerte" Date sample received 16.4.73 4.4.74

Mean weight (g) 184.3 459.2 248.8 Water (%) 66.9 82.0 73.1 Oil (%I 22.9 12.3 17.8 Calorific value (ca1/100 g)b 232 123 183 Composition of dry matter Oil (%I 69.2 68.3 66.2 Protein (%) 4.8 8.9 7.1 Ash ( %) 4.8 6.1 4.8 Fibre ( %) 5.7 7.8 7.1 Acidity (as % citric acid) 0.82 0.67 0.48 Carbohydrate (%) 14.7 8.2 14.3 Sodium (mg/100 g) 15 50 16 Potassium (%) 1.5 1.7 1.6 Typical half' Weight (g ) 65 161 87 Water (g) 42.8 132.0 64.2

Oil (9) 14.7 10.8 15.0 Calorific value (cal)b 148 198 157

Potassium (mg) 320 507 371

Range of weights (g) 130-226 419-500

Protein (g) 1 .o 2.6 2.0

Sodium (mg) 3 14 4

a Mean values from Table 2. * Calculated by method prescribed in The Labelling of Food Regulations

1970 (SI 1970 No. 400). Based on mean figure for edible matter of 70 %.

3.4. Carbohydrate Unlike most of the previously published datalo the figures for carbohydrate and fibre are quoted separately in Tables 1,2 and 3. On the wet basis the carbohydrate varied from 2.9 to 6.4 %, but after the early part of the season the figures are reasonably consistent when calculated on the dry matter. The flesh contained 0.5-2.2% reducing sugars, but no sucrose was detected. Such figures are probably of minor significance however as it is well known that the level of sugar decreases rapidly during storage and ripening, so they are dependent on growth conditions, the time of picking and the length of storage prior to the analysis. Israeli fruits gave a wider range of figures than those from South Africa. The fibre content does not vary significantly except in the case of the market decrease over the South African season when calculated on the dry basis.

3.5. Acidity The acidity of avocado flesh is low, the highest figure being found in early season South African fruits, viz. 0.31 % (as citric acid). There was however a significant fall as both seasons progressed whether the figures are calculated on the wet or the dry basis.

212 D. Pearson

3.6. Mineral matter The mineral content of avocado is higher than that recorded for any other fruit.16 The ash of the Israeli fruits (1.0-1.6 %) is slightly higher than in South African avocados (0.8-1.2 %). When considered on the dry basis the ash of South African fruits falls to a much greater extent over the season than with the Israeli avocados. The potassium and sodium figures found are of the same order as those reported in the more recent liter- ature: presumably using similar instrumental techniques (cf. Winton and Wintoii3 and Jaffe and Gross16). Over the seasons the potassium (wet basis) and the potassium- ash ratio are much less variable than the potassium in the dry matter.

3.7. Calorific value The energy values in avocados are contributed almost entirely by the oil present. As the oil content rises as the season progresses, the calorific values per 100 g of edible flesh also increase. As this is mainly of dietary interest, it is more important to take this into account with the weight of fruit normally consumed. Thus there is a general trend over the season for the fruit weight to fall as the oil content increases. In consequence the calorific values of the “typical half” do not show such a large increase as when cal- culations are expressed as a function of the edible flesh. This is particularly marked with Israeli avocados where the calorific values of the typical half remained fairly constant from December 1973 to February 1974.

As the calorific value is mainly dependent on the oil content it can be readily calcul- ated approximately from the following expression (all figures on the wet flesh basis) :

C=9.07 Ff21 .2 (1) where C = calorific value expressed as kilocalories per 100 g and F = % oil in the

avocado flesh. Also if Wis the percentage of water:

F + W = 90.9 (2)

(3) Therefore F = (90.9 - w> ? 1.6

From (1) and (3) it is apparent that the calorific value can also be readily obtained with sufficient accuracy for most practical purposes from the easily determined water figure :

C = 846 - 9.07 W (4)

4. Conclusions

Samples of high quality avocados obtained at Covent Garden market showed some sig- nificant monthly changes in composition. In general the values obtained show similar trends to those reported on fruits examined in growing areas of the United States. The avocado is exceptional among fruits in that it contains more protein and mineral matter and much more oil. The author found oil contents up to 40 % in South African fruits, whereas the highest figure reported in the literature is 31.6 for Californian avocados. The water/fat ratio varies from about 1.3/1 to 7.4/1 and decreases as the commercial season progresses in both South African and Israeli fruits. Figures for individual fruits and average figures therefore may be misleading and there are advantages with

Seasonal variations in composition of avocados 213

some components in calculating the data on the fat-free basis. Apart from compositional data the weights of individual avocados tend to fall as the season progresses and it is advisable to make calculations for dietary purposes on the typical half.

Acknowledgements The author would like to express his gratitude to Mrs M. Fraser, Mr T. Piper and especially Mrs S. Welham, who carried out most of the analyses. Thanks are also due to Mr R. H. Skinner for assistance with calculations, and to the South African Avocado Growers Association and the Agrexco Agricultural Export Co. Ltd for arranging the regular supply of representative samples.

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McCance, R. A.; Widdowson, E. M. The Chemical Composition of Foods HMSO, London. 1967, 3rd edition, p. 74. Platt, B. S. Tables of Representative Values of Foods commonly used in Tropical Countries Medical Research Council, Special Report Series No. 302, HMSO, London. 1962, p. 18. Watt, B. K.; Merrill, A. L. Composition of Foods-Raw Processed Prepared Agricultural Hand- book No. 8, U S Department of Agriculture, Washington D.C. 1963, p. 7. US Department of Health, Education and Welfare. Food Composition Table for Use In East Asia FAO. 1972, p. 77. Private communication from Agrexco Agricultural Export Co. Ltd, London. Stahl, A. L. Changes in Composition of Florida Avocados in Relation to Maturity Bulletin 259, Agriculture Experiment Station, Gainesville, Florida. May 1933. Biale, J. B.; Young, R. E. In The Biochemistry of Fruits and their Products Hulme, A. C. (ed.), Academic Press, London. 1971, Vol. 2, pp. 1-63. Pearson, D. Laboratory Techniques in Food Analysis Butterworth, London. 1973. Pearson, D. The Chemical AnuZysis of Foods Churchill, London. 1970, 6th edition. The Fertilisers and Feeding Stuffs Regulations HMSO, London. 1973 (SI 1973 NO. 1521). The Labelling of Food Regulations HMSO, London. 1970 (SI 1970 No. 400). Collins, G. C.; Polkinhorne, H. Analyst (Lond.) 1952,77,430. Jaffe, M. E.; Gross, H. Univ. Calif. agric. exp. Sta. Bull. 1923,365,630.

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