Storage conditions and ripening of chiku fruits Achras sapota L.

Scientia Horticulturae, 10 (1979) 377--385 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

377

STORAGE CONDITIONS AND RIPENING OF CHIKU FRUITS ACHRAS S A P O T A L.

W.J. BROUGHTON1and H.C. WONG

Department of Genetics and Cellular Biology, University of Malaya, Kuala Lumpur (Malaysia) Present address: Institut fiir Obstbau und Gemiisebau der Universit~/t Bonn, Auf dem Hiigel 6, 5300 Bonn (Federal Republic of Germany) (Received 15 August 1978)

ABSTRACT Broughton, W.J. and Wong, H.C., 1979. Storage conditions and ripening of chiku fruits Achras sapota L. Scientia Hortic., 10: 377--385. Chiku fruits (Achras sapota L.) were found to be climacteric with the respiratory peak occurring at the same time, or 1--2 days after peak ethylene production. The optimum storage temperature was near 20° C. Storage life at this temperature could be increased by removing ethylene (C 2H4 ) and adding 5--10% (v/v) carbon dioxide (CO 2) to the storage atmosphere. Extreme relative humidities or high concentrations of CO 2impaired the quality of stored fruits. Ripening was not affected by treatment with oxygens. C~H4 or indoleacetic acid. Ascorbic acid and glucose levels increased with ripening but ascorbic acid decreased when the fruit became over ripe. Recommended storage conditions are about 20°C with 5--10% CO 2 coupled with the complete removal of C2H4 from the storage atmosphere. Short-term holding of the fruit at lower temperatures is also possible.

INTRODUCTION The c h i k u (Achras sapota L.) belongs t o t h e Sapodilla family. It is indigen o u s t o S o u t h America, b u t has been cultivated in m o s t tropical c o u n t r i e s f o r centuries (Hayes, 1 9 7 0 ; Allen, 1975). The w o r d c h i k u is derived f r o m the A z t e c n a m e o f chikl (Allen, 1975). When t h e fruit is ripe, the flesh is soft, p u l p y and granular w i t h a sweet and delicate taste. O n a c c o u n t o f its taste and l o w cost o f p r o d u c t i o n , it is o n e o f t h e m o r e p o p u l a r Malaysian fruits. Fruit are p r o d u c e d t h r o u g h o u t t h e y e a r b u t p r o d u c t i o n is n o t u n i f o r m . As a single tree can bear h u n d r e d s of fruits, m a n y are available at peak seasons. Unless o p t i m a l storage c o n d i t i o n s are devised, m a n y fruits are wasted. This c o m m u n i c a t i o n , t h e r e f o r e , deals with elucidating t h e o p t i m a l ripening and storage c o n d i t i o n s for chikus.

378 EXPERIMENTAL Fruits. -- Chikus were obtained from a garden in Petaling Jaya, Selangor.

Average weight of the fruits ranged from 75 to 100 g and they measured 6--8 cm across the widest portion. Fruits were picked hard, unripe but mature. Vaseline was applied to the cut end of the fruits to prevent dehydration and fungal infection. They were then weighed and placed in gas-tight "Kilner" jars. Details of this technique have been given previously (Broughton et al., 1977). E f f e c t o f temperature, relative humidities, o x y g e n tension, C02 tension and C2H4 tension on storage and ripening. -- Temperatures were regulated b y

placing the jars in incubators at different temperatures. Relative humidity, and gas tensions were controlled b y adding or removing the appropriate substance from the storage atmosphere. Visual assessments of appearance, as well as the taste of the fruit were performed at regular intervals. All experiments were performed as described by Nazeeb and Broughton (1978). In each of the treatments, a single fruit was used per replicate. All results are means of at least triplicate determinations. E f f e c t o f transfers. - - Fruits were stored at 4°C for 10 or 28 days after which

they were transferred to 20°C. E f f e c t o f hormones. -- Fruits were dipped daily in indole-3-yl-acetic acid

(IAA) at concentrations of 10 -3 M, 5 × 10 -3 M and 10 -2 M and incubated at 20°C until they ripened. C02 and C2H4 determination. - - T h e s e were assayed b y titrimetry and gas chromatography, respectively, as described by Broughton et al. (1977). Ascorbic acid, glucose and starch determination. -- Fruits at different stages

of ripeness were selected and their ascorbic acid, glucose and starch levels determined. The ascorbic acid content was determined by the 2,6-dichlorophenol-indophenol method (see SebreU, 1967) and glucose b y the glucose oxidase-peroxidase method (Bergmeyer and Brent, 1965). The procedure for starch determination was essentially similar to that for glucose determination. To a portion of the homogenate (from the sample for glucose determination), 5 mg each of a-amylase (1300 units/mg solid) and H-amylase (12 units/mg solid) were added. Then the mixture was incubated at 37°C for 30 min and centrifuged for 20 min at 10 000 × g at 4°C. Glucose content of the enzyme-treated supernatant was analysed using the glucose oxidase-peroxidase method. The amount of starch present was defined as the difference in glucose content of the supernatant before and after enzyme treatment, and was expressed in glucose equivalents.

379 - - Glucose oxidase (E.C.1.1.3.4.), peroxidase (E.C.1.11.1.7), o-dianisidine, s-amylase (~-1, 4-glucan 4-glucanohydrolase E.C.3.2.1.1. Bacterial Type IIA),/3-amylase (/3-1, 4-glucan maltohydrolase E.C.3.2.1.2 from barley crude type IIB), 2, 6-dichlorophenol, indophenol, and indole3-yl-acetic acid (IAA) were obtained from the Sigma Chemical Co., St. Louis, Missouri. Carbon dioxide and oxygen were obtained from Far East Oxygen Limited, Kuala Lumpur. Chemicals.

RESULTS A c h r a s s a p o t a is a climacteric fruit as seen from Fig. 1. At higher temperatures, the rate o f respiration and C2H4 production were correspondingly higher and the peaks of C2H4and CO2 production also occurred earlier (Fig. 1, Table 1). At 25°C, fruits attained the eating-ripe stage after 9 days in storage and rotted after the 13th day. At 20°C, they took 10 days to ripen and remained in a good condition for another 5 days. At 15°C, the fruits could be stored for 22 days. At this temperature, however, normal ripening failed to occur in most o f the trials. Fruits ripened at 20°C and at 25°C had excellent taste while those ripaned at 15°C were not as good. Of the 3 temperatures studied, 20°C seemed to be the most suitable, in that the normal ripeningprocess was slowed without any effect on fruit quality. Thus, subsequent experiments to extend or shorten the green life of chikus were carried out at this temperature. Fruits which were stored at 4°C for 10 days ripened normally when transferred to 20°C, and had a shelf life of 24 days (Table 1). The quality of fruit ripened, however, was similar to those which occasionally ripened at 15°C. (Q)

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Fig. 1. (a) Rate o f C 2 H 4 e v o l u t i o n b y chikus stored at different temperatures. Fruits were placed in Kilner jars and stored at 15, 2 0 or 25°C. Daily aeration o f the fruit and determination o f C~H 4 evolved were performed. (b) Rate o f CO 2 e v o l u t i o n b y c h i k u s stored at d i f f e r e n t temperatures.

380 TABLE 1 S u m m a r y o f the effect o f various t r e a t m e n t s on the onset of the climacteric, C~ H 4 production, final taste and appearance of chikus Treatment

Days t o reach C 2 H 4 peak

Days to reach CO 2 peak

Shelf-life (days)

Quality and appearance

4 5 8 16 31

5 5 9 16 33

13 15 22 24 44

Taste e x c e l l e n t Taste excellent Taste satisfactory Taste satisfactory Failed to ripen normally

Wet

9

9

14

Dry

6

7

13

Taste satisfactory, soggy appearance Taste satisfactory, wrinkled appearance

+5

5

5

13

+ 10

6

6

12

+15

7

5

12

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10

10

15

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18 21 29 15

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6 3 5 29

13 11 11 39

Taste Taste Taste Taste

4 7

10 16

Appearance soggy Taste fiat

T e m p e r a t u r e (°C) 25 20 15 4 (10 days) 4 (28 days) Relative h u m i d i t y

O~(%) Taste and appearance satisfactory Taste and appearance satisfactory Taste and appearance satisfactory Taste and appearance satisfactory

CO,(%) + 5 +10 +20 0

C ~ H 4 (mg/l) +50 +i00 +200

-C2H4

m

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good good good good

IAA 10-2M 5 × 10"3M

381

When the storage time at 4°C was increased to 28 days, the fruit failed to ripen normally u p o n transfer to 20°C. Compared to the control fruits, i.e. those stored in unmodified air, the climacteric was delayed in both the dry and wet treatments (Table 1). As a result, ripening was also delayed. Fruits ripened under the low relative-humidity treatment were wrinkled and shrivelled while those in the wet environment were soggy and the eating-quality was poor. In both treatments, the shelf life was only 2 weeks, which was similar to that of the control fruits (Table 1 ). Except for the greater production of C2H4 at higher 02 tensions, O: levels higher than those in air caused no obvious change in the respiratory or C:H4 production curves (Table 1). Both ripening-time and shelf life were similar to that of the control fruits. Taste and appearance were normal. On the other hand, both the climacteric and ripening were delayed when 02 was removed from the storage atmosphere. Higher concentrations of CO2 increasingly delayed the climacteric and ripening (see Fig. 2a, Table 1), yet the quality of fruits ripened under 5 or 10% (v/v) COs was comparable to that of the control fruits. Fruits ripened under 20% (v/v} COs looked and tasted poor. Removal of COs from the storage atmosphere delayed the climacteric as compared to control fruit b u t the climacteric occurred earlier in treatments incorporating exogenous COs (Fig. 25). 18

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Fig. 2. (a) Effect of different levels of CO 2 on the rate of C2 H+ evolution by c h i k u s stored at 20°C. (b) Effect of CO 2 removal from the respiration c h a m b e r on the rate of C: H+ evolution by c h i k u s stored at 20°C.

382

Application of exogenous C2H4 had no apparent effect on the climacteric and ripening of chikus (Table 1). On the other hand, removing the C2H4 produced by the fruits delayed the climacteric by 23 days (Table 1). Fruits ripened under both treatments were comparable in taste and appearance to the controls. IAA increased the amounts of CO2 and C2H4 produced by the fruit, but had no significant effect on the onset of the climacteric (Table 1). IAA-treated fruits, however, had a flat taste. Levels of glucose increased with progressive ripening, while the level of starch decreased in harmony with this (Fig. 3). Ascorbic acid contents also increased with ripening, but fell when the fruits became over ripe (Fig. 4). 'T

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Fig. 3. Changes in glucose and starch contents of ripening chikus. Fruits at different stages of ripeness were selected and their starch and glucose contents analysed. Stage (1) preclimacteric phase. Stage (2) at the climacteric rise. Stage (3) at the climacteric peak. Stage (4) after the climacteric peak. Stage (5)just before spoilage. DISCUSSION

At higher temperatures, the rate of respiration of chikus was greater and the fruits ripened and deteriorated faster. Short-term holding of the fruits at 4°C before storing at 20°C extended their storage life. Yet normal ripening occurred only if the duration of exposure was less than 10 days. Too long an exposure to 4°C resulted in chilling-injuries which are a function of temperature as well as duration o f exposure (Tomkins, 1959; Fidler and

383

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Fig. 4. Changes in t h e ascorbic acid c o n t e n t s o f ripening chikus. The same set o f fruits was used as in Fig. 3. Thus t h e stages o f ripeness listed t h e r e a p p l y here also.

Coursey, 1969). Singh and Mathur (1954) found that chilling-injury of

Achras sapota occurred at temperatures less than 1.6°C. This discrepancy could be due to cultivar differences or to differences in exposure periods. At 20°C, both a highly saturated and a dry environment seemed to prolong the storage life of chiku. Behaviour of chikus in the dry environment was unexpected, as several workers have reported that dry atmospheres hasten ripening (see Broughton et al., 1977; Broughton and Wu, 1979; Nazeeb and Broughton, 1978). Phan et al. (1973) advocated a relative humidity of 85--90% for optimal storage of chiku, which is in accord with the present findings. The fruits ripened under too high or too low relative humidity were of poor quality. While low 02 tensions invariably delayed ripening, levels higher than those in air had no apparent effect on chikus. Similar observations were made by Biale et al. (1954) for avocados (Persea americana) and Dull et al. (1967) for pineapples (Ananas cosmosus). Maintaining chikus under high CO2 concentrations prolonged the storage life, presumably due to respiratory inhibition. Five % (v/v) and 10% (v/v) CO2 in the storage atmosphere did not cause injury, but 20% CO2 was deleterious. Different fruits seem to have different levels of CO2 susceptibility.

384 Tomkins (1959) found, for example, that 5% (v/v) CO2 injured Cox's Orange Pipin apples (Malus pumila), while Nazeeb and Broughton (1978) found normal ripening in papayas (Carica papaya) stored at this concentration. Wilkinson (1970) advocates 15--30% CO2 for short-term holding of cherries (Prunus avium ), grapes (Vitis vinifera), plums (Prunus americana) and strawberries (Fragaria spp). Wang and Mellenthin (1975) found that 12% (v/v) CO2 was not injuriaus to Pyrus communis. Wilkinson (1970) attributes CO2 injury to the fact that excess CO: inhibits the metabolism of acetaldehyde, which is a tissue poison. Removal of CO2 did not hasten the climacteric or the ripening of chikus. This is different to the situation occurring in most tropical fruits (Broughton et al., 1977; Nazeeb and Broughton, 1978; Broughton and Wu, 1979; Broughton and Leong, 1979). Burg and Burg (1967) suggested that CO2 was a competitive inhibitor of C2H4 action. Thus removal of CO2 would render C2H4 more effective. With chikus, both the removal and addition of CO: caused an upset in C2H4 production. In the early stages of ripening, very little C2H4 was produced. Perhaps the role of CO2 in the control of the post-harvest physiology of chikus is more complicated than in other fruits. Removal of C2H4 delayed ripening in chiku without any adverse effect on the quality of the fruit. Similar observations have been reported for other fruits (Forsyth et al., 1969; Scott et al., 1971; Broughton et al., 1977; Nazeeb and Broughton, 1978; Broughton and Wu, 1979; Broughton and Leong, 1979). Surprisingly, application of exogenous C2H4 did not accelerate the ripening of chiku. Chikus do not seem to be affected by IAA, although reaction to IAA differs with species. Lampe (1971) reported a delaying effect on tomatoes (Solanum lycopersicum). Broughton and Leong (1979) found, however, that IAA hastened the ripening of guavas (Psidium gua]ava). Levels of glucose increased with a corresponding decrease in starch as chikus ripened. Glucose contents levelled off at the ripe stage and did not decrease with post-ripening as in papayas, Carica papaya (Nazeeb and Broughton, 1978) and bananas, Musa spientum (Broughton et al., 1979). Levels of ascorbic acid increased with ripening but decreased during the over-ripe phase. With the above in mind, the recommended temperature range for both optimal storage and ripening of chikus is 15--20°C. If further extension of the storage life is desired, the fruits could be stored in an atmosphere containing 5--10% (v/v) CO2, devoid of C2H4and with a relative humidity of 85--90%. Storage at lower temperatures (e.g. 4°C) for a few days is also possible. ACKNOWLEDGEMENTS We wish to thank Mohammed Nazeeb for his excellent technical assistance, and Dr. Hashim bin Abdul Wahab for his continued support. Financial assistance was provided by the Malaysian Agricultural Research and Development Institute :(M.A.R.D.I.) and by the University of Malaya.

385 REFERENCES Allen, B.M., 1975. Common Malaysian Fruits. Longmans, London, pp. 44--46. Bergmeyer, H.U. and Brent, E., 1965. Determination of glucose with glucose oxidase and peroxidase. In: H.U. Bergmeyer (Editor), Methods of Enzymatic Analysis. Verlag Chemie, GmbH., Weinheim/Bergstr., pp. 123--128. Biale, J.B., Young, R.B. and Olmstead, A.J., 1954. Fruit respiration and ethylene production. Plant Physiol., 29: 168--174. Broughton, W.J. and Leong, S.F., 1979. Maturation of Malaysian fruits. III. Storage conditions and ripening of guava. (Psidium guajava L. var. G.U. 3 and G.U. 4). M.A.R. D.I. Res. Bull., in press. Broughton, W.J. and Wu, K.F., 1979. Storage conditions and ripening of two cultivars of banana. Scientia Hortic., 10: 83--93. Broughton, W.J., Hashim, A.W., Shen, T.C. and Tan, I.K.P., 1977. Maturation o f Malaysian fruits. I. Storage conditions and ripening of papaya (Carica papaya L. var. Sunrise Solo). M.A.R.D.I. Res. Bull., 5: 59--72. Broughton, W.J., Chan, B.E. and Kho, H.L., 1979. Maturation of Malaysian fruits. II. Storage conditions and ripening of banana (Musa sapientum L. var. Pisang Emas). M.A.R.D.I. Res. Bull., in press. Burg, S.P. and Burg, E.A., 1967. Molecular requirement for the biological activity of ethylene. Plant Physiol., 42: 144--155. Dull, G.G., Young, R.E. and Biale, J.B., 1967. Respiratory pattern in fruits of pineapple Ananas cosmosus, detached at different stages of development. Physiol. Plant., 20: 1059--1065. Fidler, J.C. and Coursey, D.G., 1969. Low temperature injury in tropical fruits. In: J.C. Fidler and D.G. Coursey (Editors), Proc. Conf. Tropical -- Subtropical Fruits. London, pp. 103--110. Forsyth, F.R., Eaves, C.A. and Lightfoot, H.J., 1969. Storage quality of McIntosh apples as affected by removal of ethylene from the storage atmosphere. Can. J. Plant Sci., 49: 567--572. Hayes, W.B., 1970. Fruit growing in India. Kitabistan, Allahabad, pp. 389--394. Lampe, C.H., 1971. Response of tomato fruits to certain growth regulators with emphasis on pectolytic enzymes, cellulose and ethylene. Diss. Abst., 32: 1308B. Nazeeb, M. and Broughton, W.J., 1978. Storage conditions and ripening of papaya 'Bentong' and 'Taiping'. Scientia Hortic., 9: 265--277. Phan, C.T., Pantastico, Er. B., Ogata, K. and Chachin, K., 1973. Respiration and respiratory climacteric. In: Er. B. Pantastieo (Editor), Postharvest Physiology, Handling and Utilisation of Tropical and Subtropical Fruits and Vegetables. Avi Publishing, Westport, Connecticut, pp. 86--103. Scott, K.J., Blake, J.R., Strachan, G., Tugwell, B.L. and McGlasson, W.B., 1971. Transport of bananas at ambient temperatures using polyethylene bags. Trop. Agric. (Trinidad), 48: 245--254. Sebrell, W.H., 1967. In: W.H. Sebrell and R.S. Haris (Editors), The Vitamins; Chemistry, Physiology, Pathology, Methods. Academic Press, New York, pp. 338--359. Singh, K.K. and Mathur, P.B., 1954. A note on cold storage o f sapotas (Achras sapota). Indian J. Agric. Sci., 24: 149--150. Tomkins, R.G., 1959. The conditions for the gas storage of certain fruits and vegetables obtained by the use of a simple small-scale method. In: M. and A.M.S. Jul (Editors), Prog. Refr. Sci. Tech., Proc. Xth Int. Congr. Refr., Copenhagen, Pergamon, Oxford, pp. 189--192. Wang, C.Y. and Mellenthin, W.M., 1975. Effect of short-term high carbon dioxide treatment on storage of Anjou pear (Pyrus communis). J. Am. Soc. Hortic. Sci., 100: 492--495. Wilkinson, B.G., 1970. Physiological disorders o f fruits after harvest. In: A.C. Hulme (Editor), Biochemistry of Fruits and their Products. Academic Press, London, pp. 537--554.