TECHNICAL BULLETIN No. 93 FEBR UARY 1977

Respiration, Ethylene Production,

and Shelf Life Extension

in Irradiated Papaya Fruit After StorageUnder Simulated Shipping Conditions

ER N EST K. AKAMINE and T HEO DO RE GOO

HAWAII AGRICULTURAL EXPERIMENT STATIO N , U NIVERSITY OF H AW AII

CONTENTS

Page

Introduction 1Materials and Methods 1Results 3

Unrefrigerated Fruit 3Refrigerated Fruit 7

Discussion and Conclusion 10Literature Cited 12

THE AUTHORS

Ernest K. Akamine is Plant Physiologist, Hawaii AgriculturalExperiment Station, and Professor of Plant Physiology, College ofTropical Agriculture, University of Hawaii.

Theodore Goo is Research Associate, Hawaii Agricultural Experi­ment Station, College of Tropical Agriculture, University of Hawaii.

ACKNOWLEDGMENTS

This research was supported in part by a grant from the UnitedStates Atomic Energy Commission (Contract No. AT(04-3)-235,Project Agreement No.5). The authors are grateful to Harry Y.Yamamoto, Food Technologist, Hawaii Agricultural ExperimentStation, and Professor of Food Science, College of Tropical Agriculture,University of Hawaii, for his assistance with gas chromatographictechniques and for his critical suggestions on the manuscript.

Received for publication October 1971 with final review by authors December1976.

Respiration, Ethylene Production,and Shelf Life Extension

in Irradiated Papaya Fruit After StorageUnder Simulated Shipping Conditions

ERNEST K. AKAMINE and THEODORE GOO

INTRODUCTION

The effectiveness of ionizing irradiation with gamma rays to extendthe shelf life of fresh fruit o f the papaya (Carica papa ya L. 'Solo') hasbeen demonstrated (4,5,6,7), and the relationship between shelf lifeextension and respiration has also been investigated (3). This technicalbulletin reports the relationship between irradiation, shelf life,respiration, and ethylene production of papaya fruit after storage underconditions simulating air and surface shipment from Hawaii to theUnited States Mainland.

MATERIALS AND METHODS

Freshly harvested papaya fruits from the Island o f Hawaii wereair-flown to Honolulu, Island of Oahu, where they were installed inexperiments on the afternoon of the day of harvest. To control storagedecay, all fruits were dipped for 20 minutes in hot water maintained at1200 F, and then they were cooled in running tap water for 20 minutes(1,2,4,5,6,7). The fruits were then irradiated with gamma rays from aCobalt'i" source at the Hawaii Research Irradiator facility. Each experi­ment used fruits of uniform maturity as judged visually b y the approxi-

2 HAWAII AGRICULTURAL EXPERIMENT STATION

mate degree of surface yellow color development. For the determi­nation of respiration and ethylene production, four replicate fruits wereused in each treatmen t.

After treatment, the fruits were stored under two sets of temperatureconditions to approximately simulate shipping conditions to the U.S.Mainland fr om Hawaii: (1) without refrigeration at 77° F for 1 day tosimulate air-shipping conditions and (2) with refrigeration at 55° F for7 days to simulate marine-shipping conditions. For the first lot, initialgas sampling was performed just prior to the Lday storage period andthen daily thereafter at 77° F. For the second lot, initial gas samplingwas performed when the fruits were remo ved from refrigeration andthen daily thereafter at 70-77° F.

For each treatment, samples of carbon dioxide (C0 2 ) for respirationmeasurements and ethylene (C2 H4 ) were taken from the atmospheresaround four fruits held separately for 1 hour in sealed gastight glass jars(volume about 6.2 liters). Gas samples of 1 to 5 milliliters werewithdrawn with a gastight syringe from each jar for analysis by gaschromatography, using a thermal conductivity detector unit (VarianAerograph 90-P) for CO 2 and a hydrogen flame ionization unit(Aerograph Hy-Fi 600-D) for C 2 H4 • The thermal conductivity detectorunit was equipped with a silica gel (powder) column in a copper tubing(internal diameter IA inch, length 14 inches). The respectivetemperatures for the column, injector, and detector were 210°, 250°,and 235° F. The carrier gas was helium maintained at a flow rate of 47ml/minute. The hydrogen flame ionization unit was equipped with analumina (60/80 screen size) column in an aluminum tubing (internaldiameter 1/8 inch, length 6 feet). The respective temperatures for thecolumn and injector were 212° and 265° F. The flow rate of the carriergas (nitrogen) and the hydrogen was 25 ml/rninute. The averageanalyses from the four replicates in each treatment are shown in theplots of results (Figures 1-7).

Between gas samplings, the fruits were held in open corrugated paperpapaya cartons at temperatures used for the CO 2 and C 2 H4

determinations. The rate of ripening and the time of the attainment ofthe edible ripe stage were also observed. A fruit was considered edibleripe when the surface was about 87 percent yellowed and yieldedslightly or readily to finger pressure. Observations were continued untilthe fruits were judged unmarketable due to decay or overripening (fruityielded very readily to finger pressure), or both.

SHELF LIFE EXTENSION IN IRRADI ATED PAP AYAS 3

RESULTS

Unrefrigerated Fruit

In a series of four experiments, fruits irradiated at 25- 28 .5, 75- 85. 5 ,125-142.5, or 250- 285 krad were studied at 77° F, a temperaturefavorable for ripening. .

In the first experiment , fruits with an initial degree of surfaceyellowing of approximately 13 percent were irradiated at 25- 28.5 krad.

0.6

0.1

--- - Ca rbo n dioxide (ha l wa ter + 25-28.5 krad)- - -- Carbon dioxi de (hot wa ter o n ly )-- --- - --- Ethy lene (h a l water + 25-28.5 krad )• ......... Eth ylen e (h a l water o n ly)

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Fig ure I. Respi rati on (CO z) a nd e thylene (C zH 4) produc­tion in 13 percent yellow papa yas hot wat ertreat ed on ly or hot wat er treat ed and irradi at edat 25-28 .5 krad , follow ed by storage a t 77° F.

4 HAWAII AGRICULTURAL EXPERIMENT STATION

The results for irradiated and unirradiated fruits are shown in Figure 1.The initial high rates of respiration were due to the high temperature(about 85- 90° F) of the fruits immediately after the hot-water dip andirradiation. Fruit temperature decreased to the temperature (77° F) ofthe storage room by the following day, and respiration also decreased.Respiration continued to decrease during days 2 and 3, then it began toincrease. The respiratory peak for the irradiated lot was attained on day4 and was slightly greater than that of the unirradiated lot, whichreached its peak on day 5. In general, the respiratory patterns of thetwo lots were similar. The fruits attained the edible ripe stage in 4 to 5days. Immediately after treatment, no C2 H4 production was detectedin either lot of fruits (Figure 1). In contrast to respiration and despite areduction in fruit temperature during day 1, production of C2 H4 inboth lots commenced and continued to increase to about the time ofthe respiratory peak. Then a rapid decrease followed. The onset ofC2 H4 production preceded the increase in CO 2 liberation by 2 days.The production of C 2 H4 was greater in irradiated than in unirradiatedfruits (Figure 1).

The results of the second, similar experiment, in which fruits withabout 25 percent yellowed surface were irradiated at a dose of 75- 85.5krad, are shown in Figure 2. As in the previous experiment, no C2H4

emanation was detected initially in either lot. During the first day, fruittemperature decreased, C 2 H4 production began, and respirationdecreased. The onset of C2 H4 production preceded by 1 day therespiratory rise (Figure 2). The C2 H4 production peak was attained 1day earlier b y the unirradiated lot, but the height of the peak wasgreater in the irradiated lot. The respiratory peak was attained on thesame day. The fruits in both lots became edible ripe on the third dayafter treatment.

In the third experiment , fruits with about 15 percent surfaceyellowing were subjected to a dose of 125-142.5 krad. The results(Figure 3) indicated that respiration and C 2 H4 production were bothgreatly altered by irradiation at this dose. The respiratory and C2 H4

production peaks were more than doubled in height, and theattainment of the peaks was delayed 3 or 4 da ys . The unirradiated lotwas edible ripe in 4 days, and the irradiated lot in 7 days. The irradiatedfruits developed blotchiness (uneven surface degreening) and scalding(surface browning). In this experiment, the onset of C2 H4 productionand the onset of respiratory rise coincided (Figure 3).

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6 HAWAII AGRICULTURAL EXPERIMENT ST AT IO N

In the fourth experiment, fru its with about 13 percent surfaceyellowing were irradiated at a do se of 250- 285 krad. An even greatereffect on respiration and C2 H4 prod uct ion occurred with this higherdose (Figure 4 ). T he resp iratory peak was increased four t ime s byirradiation, an d the attainment of the peak was delayed 2 days. TheC2 H4 peak was increased five times, and the attainment of the peakwas delayed 2 days by irradiation. The unirradiated fruits were edible

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Fig-ure 4. Respiration (C0 2 ) and ethylen e (C 2 H 4 ) produc­tion in 13 percent yellow papayas hot watertreat ed on ly or hot water treated a nd irradiatedat 250-285 krad, followed by sto rage at 77° F.

SHELF LIFE EXTENSION IN IRRADIAT ED PAP AYAS 7

ripe in 3 days. The irradiated fruits, o n the ot he r hand, were severelyscalded and failed to ripen, remaining firm throughout the storageperiod until attacked b y decay organ isms. There was again asimultaneous onset of respiratory rise and onset of C2H4 production(Figure 4).

Refrigerated Fruit

In a series of four experiments, papayas given the same irradiationdoses as in the previous series, except for the highest dose, were studiedat 70-77° F a fter refrigeration at 55° F. Respiration and C2H4 studies

5

--- -- Carbon di oxide (ho t wat er + 25-28.5 krad )- - -- Carbon di oxide (ho t wat er o n ly)- - - - -- - Eth ylen e (ho t wat er + 25-28.5 krad )•• - .. •••• Eth ylene (ho t wa ter on ly)

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Figu re 5. Respirati on (C0 2 ) and ethy lene (C Z H 4 ) p roduc­tion a t 77° F in 13 percent yellow papayas hotwa ter treat ed on ly o r hot wa ter treat ed and ir­ra d ia ted a t 25-28. 5 kr ad , followed by storagein itia lly a t 55° F fo r 7 days th en a t 77° F.

8 HAWAII AGRICULTURAL EXPERIMENT STATION

were conducted on the fruits immediately upon removal from coldstorage and daily thereafter .

The first ex periment used fruits of about 13 percent yellow colorirradiated at 25- 28.5 krad. As expected, immediately upon removalfrom refrigerated storage, CO 2 liberation was very low, and C2 H4

production was nil (Figure 5). After 1 day at 77° F, CO 2 prod uct ionincreased about six times; and C2 H4 production had commenced.There was no further increase in respiration after the first day, butC2 H4 emanation contin ued to increase, reaching the peak productionin 3 days. The respiratory behavior of the irradiated and unirradiatedfruits was similar, but the peak for C2 H4 production was greater for theirradiated fruits (Figure 5) . The fruits in the two lots were edible ripeabout the third day after removal from cold storage.

----Ca rbo n diox ide (ho t wat er + 75-85.5 kra d )- --- Ca rbo n d ioxide (ho t wat er on ly)- - - - - --- - Ethy lene (ho t wa ter + 75-85.5 krad ) 5•• • •..• . . • Ethylene (ho t wa ter on ly)

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Fig-me 6. Respiration (CO 2) a nd ethy lene (C 2 H 4) produc­tion at 72° F in 13 percent yellow papayas hotwater treated only or hot water treated and ir ­radiated a t 75-85 .5 krad , followed by storageinitially at 55° F for 7 da ys th en at 72° f.

SHELF LIFE EXTENSION IN IRRADIATED PAPAYAS 9

In the second experiment, papayas of about 13 percent color stagewere irradiated at a dose of 78- 85. 5 krad. After removal from coldstorage to 72 0 F, respiration increased during day 1 (Figure 6) andcontinued to inc rease on days 2 , 3, and 4, whe n the peak was reached.The ethylene peak was attained during day 3. In general, respirationand C2 H4 production were the same for irradiated and unirradiatedfruits except that after the peak prod uct ion , unirradiated fruits

----Carbon d io x ide (ho t wat er + 125-1 42.5 krad )----- Ca rbo n di oxide (ho t wat er o n ly )- - ------ Eth ylene (ho t wa ter + 125- 142.5 krad )•• " • •• • • • •Ethy lene (hOI wa ter o n ly) 0.7

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Figure 7. Resp ira tion (C0 2 ) and ethylene (C Z H 4 ) produc­tion at 700 F in 10 percent yellow papayas hotwater treated only or hot water treated and ir­radiated a t 125-142.5 krad, followed by storageinitially at 550 F for 7 days then at 700 F.

10 HAWAII AGRICULTURAL EXPERIMENT STATION

produced more C2 H4 • The edible ripe stage of fruits occurred on day 5for unirradiated fruits and on day 7 for irradiated fruits. The irradiatedfruits in this experiment were slightly scalded.

The results shown in Figure 7 concern papayas of about 10 percentyellow stage irradiated at 125-142.5 krad and studied at 70° F afterrefrigeration (the third experiment). A repeat of this experiment (thefourth experiment) produced similar results (not shown).

The initial maturity of the fruit and the post-refrigeration storagetemperature of this third experiment were similar to those of thesecond experiment, yet the respiratory and C2 H4 patterns weresomewhat different. The respiratory peak was attained about 1 daylater in this experiment (Figure 7) than in the previous experiment(Figure 6). The respiratory rate was greater in irradiated papayas thanin unirradiated fruits in this experiment (Figure 7), compared withsimilar respiratory patterns for unirradiated and irradiated fruits when alower irradiation dose was used (Figure 6). Peak C2 H4 production forthe two lots was attained at the same time in the previous experiment(Figure 6), whereas the peak of the irradiated fruits appeared 1 dayearlier than that of the unirradiated fruits-in this experiment (Figure 7).The reduction in C2 H4 emanation due to irradiation was much greaterfor the higher dose treatment (Figure 7) than for the lower dosetreatment (Figure 6). Unirradiated fruits were edible ripe in 5 days andthe irradiated fruits in 7 days. The irradiated fruits were scalded.

DISCUSSION AND CONCLUSION

An irradiation dose of 25-28.5 krad is ineffective for delaying theoccurrence of the respiratory peak and thus the rate of ripening inunrefrigerated (Figure 1) as well as refrigerated papaya fruits (Figure 5),which confirms the findings of previous investigations (7). Theseprevious investigations established that, even with the optimal dose forshelf life extension (about 75 krad), the rate of ripening is not reducedin fruits with 25 percent or more of initial surface coloration, and thisphenomenon is shown again in the present experiment, in which 25percent yellow fruits irradiated at a dose of 75- 85.5 krad attained therespiratory peak on the same day as unirradiated fruits (Figure 2).

SHELF LIFE EXTENSION IN IRRADIATED PAPAYAS n

Refrigeration reduced the difference in respiratory response betweenirradiated (75-85.5 krad) and unirradiated fruits with 13 percent initialsurface color (Figure 6). However, irradiation delayed the attainment ofthe edible ripe stage by approximately 2 days.

In papayas irradiated at a relatively high dose of 125-142.5 krad, theappearance of the respiratory. peak was delayed in fruits stored at 77° F(Figure 3). When refrigerated at 55° F, the appearance of therespiratory peak was not delayed (Figure 7). In both cases, theattainment of the edible ripe stage was delayed 2 or 3 days. In papayasirradiated at a higher dose of 250-285 krad, followed by storage at77° F, there was a great delay in the appearance of the respiratory peak(Figure 4), but the fruits were severely injured and failed to ripennormally.

Whether C2 H4 triggers the onset of the respiratory rise or whetherC2 H4 is merely a by-product of respiration has been of academicinterest for some years. Earlier work (8,9) provided no evidence ofC2 H4 being the trigger mechanism for the respiratory rise. In recentyears, with the advent of more sensitive instrumentation for C2 H4

detection, more evidence is being accumulated in support of theconcept that C2 H4 is the trigger (10,11). The relationship betweenthese two physiological processes can be analyzed in the results of thefour experiments that were conducted at 77° F. In two of theexperiments, in which the fruits were not scalded, the onset of C2 H4

production preceded by 1 to 2 days the onset of respiratory rise in boththe irradiated and unirradiated fruits (Figures 1 and 2). However, in theother two experiments, in which the irradiated fruits were scalded, thetwo processes coincided in both lots of fruits (Figures 3 and 4). Thisseems to be an inconclusive evidence that the C2 H4 maybe the triggerfor respiration in treated papayas, provided the fruits can tolerate thetreatments.

12 HAWAII AGRICULTURAL EXPERIMENT ST AT IO N

LITERATURE CITED

1. Akamine, E. K. 1960. Temperature effects in fresh papayas processed for

shipment. Hawaii Agr. Exp, Sta. Bull. 122. 14 pp.

2 . , and T. Arisumi. 1953. Control of postharvest storage decay of fruits

of papaya (Carica papaya L.) with special reference to the effect of hot water.

Proc. Amer. Soc. Hort. Sci. 61: 270-274.

3. , and T. Goo. 1967. Preliminary studies on respiration of

gamma-irradiated fresh fruits, In Dosimetry, tolerance, and shelf life

extension related to disinfestation of fruits and vegetables by gamma

irradiation. Division of Isotopes Development, United States Atomic Energy

Commission, Contract Number AT(04-3)-235, Project Agreement No.5.

Annual Report June 1,1966 to May 31, 1967. pp. 127-139.

4. , and . 1969. Effect of gamma irradiation on shelf life

extension of fresh papayas. In Dosimetry, tolerance, and shelf life extension

related to disinfestation of fruits and vegetables by gamma irradiation.

Division of Isotopes Development, United States Ato mic Energy Commission,

Contract Number AT(04-3)-235, Project Agreement No.5. Annual Report

June 1, 1968 to May 31,1969. pp. 33-53.5. , and R. Wong. 1965. Shelf life extension of papayas with gamma

irradiation. In Dosimetry, tolerance, and shelf life extension related to

disinfestation of fruits and vegetables by gamma irradiation. Division of

Isotopes Development, United States Atomic Energy Commission, Contract

Number AT(04-3)-235, Project Agreement No.5. Annual Report June 1,

1964 to May 31,1965. pp. 55-75.6. , and . 1966. Refrigerated storage of irradiated papayas. In

Dosimetry, tolerance, and shelf life extension related to disinfestation of

fruits and vegetables by gamma irradiation. Division of Isotopes

Development, United States Atomic Energy Commission, Contract Number

AT(04-3) -235, Project Agreement No.5. Annual Report June 1, 1965 to May

31, 1966.pp. 17-26.

7. , and R. T. F. Wong. 1966. Extending the shelf life of papayas with

gamma irradiation. Hawaii Farm Sci. 15(1):4-6.

8. , R. E. Young, and J. B. Biale. 1957. Respiration and ethylene

production in the purple passion fruit. Proc. Amer. Soc. Hort. Sci.

69:221-225 .

9. Biale, J. B., R. E. Young, and A. J. Olmstead. 1954. Fruit respiration and

ethylene production. Plant Physiol. 29: 168-1 74.

10. Hansen, E. 1966. Postharvest physiology of fruits. Ann. Rev. Plant Physiol.

17:459-480.

11. Pratt, H. K., and J. D. Goeschl. 1969. Physiological roles of ethylene in

plants. Ann. Rev. Plant Physiol. 20:541-584.

DISCLAIMER

Reference to a com pany or product name does not imply approvalor recommendation of th e product by the College of Tropical Agri ­culture, Univers it y of Hawaii , or the United States Department ofAgricu lture to the exclusion of others that may be available .

Single copies o f th is p u blica tio n ava ila ble wi thout cha rge to Hawaii resi den ts from co untyagr-nts. O u t-of -Sta te inq uiries or bulk orders sho u ld be sent to the Co llege of Tropica l Agri­cu lturc O rcin Desk , Room 108 Krauss Ha ll, 2500 Do le Street , Honolu lu, Hawa ii 96822 .Prire per co py 10 bu lk users, thirt y cen ts p lus postag e.

Hawaii Agricultural Experime n t StationCollege of Tropical Agricu lt ure, U nivers ity of H awaiiWill ia m R. Furt ick, Dean o f the Co llege and Director o f the Exper im ent StationNoel P . Kefford, Acting Asso cia te Di rector of the Ex pe rime n t Sta tio n

T ech . Bull. 93-February 1977 (2M )