DENNISON ET AL: IRRIDATION OP CITRUS RUIT 285 IRRADIATION O DUNCAN GRAPERUIT, PINEAPPLE AND VALENCIA ORANGES AND TEMPLES R. A. Dennison1, W. Grierson2, and E. M. Ahmed1 Abstract Irradiation with dosages above 1 krad in duced some decay reduction in Pineapple and Valencia oranges stored at for s without diphenyl pads. At there was less spoilage for the Temple fruit; with diphenyl pads and storage at there was less spoilage of Pineapple oranges. The citrus fruits exami ned showed irradiation induced peel injury. Tem ple fruit were the least susceptible to peel injury. The severity of peel injury was greater as the radiation doses increased or the storage temper ature and duration increased. lorida Agricultural Experiment Stations Journal Series No. 2543. ldepartment of ood Science, University of lorida, Gainesville. 2University of lorida Citrus Experiment Station, Lake Alfred. There were no differences in the organoleptic quality attributes of irradiated grapefruit stored 19 and 2 s at 65 and 58, respectively. No differences were observed in the color or consistency of juice expressed from irradiated Valencia oranges, but a lower flavor rating was obtained from the krad level. Sections from Temple fruit irradiated with dosages in excess of 1 krad and stored s at 35 and 5 were softer and had less acceptable flavor. How ever, by extending the storage period to 13 s, no differences were observed in the flavor of Temples stored at 5. In view of the severity of peel injury irradia tion cannot be recommended for preservation of lorida citrus fruits. Introduction There is a widespread interest in the use of gamma radiation for the extension of shelf life of citrus fruits. While decay organisms can be inactivated by adequate dosages of gamma Table 1. Effects of irradiation, storage temperature and duration, and diphenyl on decay (%) and peel injury (points scale) in Duncan grapefruit. Storage Temp. Period!/ ] Dose (krad) 1 P.I, Without 1.9 1.9 1.9 6.9 1.9 1.6 Diphenyl 6.9 19.8 52. 8.2 25. 88.4 3.4 9.5 12. 1.9 5.2 6.5 11. 1.9 1.9 6. 1.8..4 1. 1.3 1. With Diphenyl 6.9.3.6 28.2 4 8.. 1.. 16.6 28. 94.5 11.8.4.6 99. 2. 5.8.2 2. 2.9 5. 8.6 4. 4.1 9.1 2. 4.3 5.8 4.6 8.8 28. 4.8 8.6 31.8 1.3 86.6 133.9 Individual fruits were scored, = none, 1 = slight, 3 = severe peel injury (1 fruits examined) 2 = medium and
286 LORIDA STATE HORTICULTURAL SOCIETY, 1966 rays, it is necessary to limit the dosage so that not more than minor changes occur in the phy sical and chemical properties of the fruit. No single radiation dose can be designated to be the minimum required for protecting cit rus fruits against spoilage. Higher radiation doses are required to retard old or established infections than incipient infections. The flux as well as the delivered dose level influence the control of infection. Beraha (1) found that de cay on oranges was not completely controlled by 182 krad3 dose delivered at 3 krad per min ute. However, he obtained effective control when the dose was delivered at 2 krad per minute over a dose range of 15 to 182 krad. By in creasing the flux rate to krad per minute, control was effective when the dose, range was 125 to 13 krad. Grierson and Dennison (4) reported a slight decay ^eduction in lorida Valencia oranges and Marsh grapefruit sub- 3One krad (kilorad) is equivalent to 1, rad. The rad is the unit which specifies the radiation dose in terms of energy absorption per unit mass. It represents an energy absorption of 1 ergs per gram of material. jected to a dose range of 1 to krad de livered at a flux rate of 6. krad per minute. Maxie et al. (6, ) found that California navel oranges irradiated with dosages up to krad were entirely free of decay for 3 months at 32 P. Guerrero et al. (5) obtained good decay control with comparatively little peel injury on irradiated California Washington navel oranges. The irradiated fruit were more susceptible to handling injury, and were less acceptable in flavor and texture. The effects of irradiation on the organoleptic characteristics of oranges and grapefruit are modified by the subsequent storage temperature and duration. Maxie et al. (6, ) found, with the exception of krad dose, no differences in the taste panel evaluations of the sections and juice from navel oranges stored up to 1 weeks at 32. The overall flavor scores, especially those treated at the lower levels of irradiation, generally improved with time after radiation. Taste panel evaluations of single strength juice prepared from whole navel oranges ex- Table 2. Effects of irradiation, storage, temperature and duration, and diphenyl on decay (%) and peel injury (points scale) in Pineapple oranges. S tor acre Temp. Period 1 Dose (krad) 1 P.I P.I Without Diphenyl 5.3 8. 9.3 5.3 6.6 8. 5 2. 5 5.6 5.6 16.9 11.9 31.6 44.6 o.o. 13.3 32..6 2. 3 9. 3 13. 3 With 8. 2.9 3. Diphenyl 12. 2 46. 3 5. 1 3.6 19.8 25.5 46. 9.4 11.5 5.5 8.2 1.9 3.8 8.8 13.8 1. 3 2. 5.4 2. 12.5 48.6.8 15.1 23.3.3 2. 2.3 9.5 24. 3.4 4.. 6 15. 3 9.8 24. 35.2 3. 23. 5 29. 4. 19.6 26.8 1.3 51.1 6.2 1/ = peel injury on a point scale. Individual fruits were scored, «none, 1 3 a severe peel injury (1 fruits examined) slight, 2 = medium and
DENNISON ET AL: IRRIDATION O CITRUS RUIT 28 posed to 3 x 1\ 6 x 1' and 1 x 1* rep1 in dicated less bitterness in the juice prepared from oranges exposed to the lowest level (3, 9). Ir radiation at 6 x 14 rep and higher increased bitterness over the controls. Irradiation with dosages up to 5 x 15 rep did not produce an off-flavor in grapefruit (2, 1). The purpose of the present study was to evaluate irradiation effects on decay control, induction of peel injury and the organoleptic quality attributes of lorida grown Duncan grapefruit, Pineapple and Valencia oranges, and Temple fruit. Materials and Methods Duncan grapefruit and Pineapple and Val encia oranges were obtained from the Citrus Experiment Station, Lake Alfred, lorida. Tem ple fruit were obtained from the Indian River 4Rep = roentgen equivalent physical which corre sponds to the amount of radiation that would bring about the same absorption of energy per unit of air or tissue as from one roentgen. Its equivalent in ergs ranges from 83 to 1 per gram of water. ield Laboratory, ort Pierce, lorida. The 1966 harvest dates for these fruits were as fol lows: grapefruit 1-24, 2-2, 3-; Pineapple 1-3, 1-1, 1-1; Valencia 3-28, 4-4, 4-11; and Temple 1-3, 2-6, and 2-13. The fruits were washed, wax ed and graded before being brought to the ood Irradiation Laboratory at Gainesville, lorida. Grading was limited to the removal of damaged or off-bloom fruit. The fruits were exposed to Co-6 gamma rays in the Mark III food irradiator to dosages of, 1,, and krad. The radiation flux was 5. krad per minute. ruits were irradi ated at 55 and with continuous exchange of air in chambers. The control and irradiated fruits were returned to the Citrus Experiment Station for further examinations. ruits were handled in ventilated cartons. There were three harvest dates of each citrus variety. At each harvest date there were four cartons for each of the irradiation levels. On return of the fruits to Lake Alfred, diphenyl pads were placed in two of the four cartons in each treatment. One carton with diphenyl pads and one carton with- Table 3. Effects of irradiation, storage temperature and duration, and diphenyl on decay (%) and peel injury (points scale) in Valencia oranges. Storaqe Tern P. Period - ^ 1 Dose (krad) P. I. P.1. Without Diphenyl.4 5. 1.2 15.4 9. 33.8 1. 19.6 46. 1. 12.6 26..4.8.8 9. 18.1.4 1.2 4.2 9.6 1 49.6 19.2 16. With Diphenyl.8 2.1.1 6.3.4 16.3.9.2 11. 1 12.1 131.9.8 1..4 11.1.4 29.4 5.3 6. 1.2 2. 5.1 5. 12.4.8 2.1 5. 4.5 8.6.4 5.2 2.9 16.1 5.4 13.5 1/ = peel injury on a point scale Individual fruits were scored, = none, 1 3 m severe peel injury (1 fruits examined) slight, 2 = medium and
288 LORIDA STATE HORTICULTURAL SOCIETY, 1966 out diphenyl pads were stored at and. ruits were examined after,, and s from harvest date for decay and peel injury. is presented as mean percentages of fruits exhibiting stem-end rot, Penicillium molds and other forms of decay. One hundred fruits from each treatment were examined for peel injury. Peel injury was rated visually with a score of for none, 1 for slight, 2 for moderate, and 3 for severe. A maximum score of would indicate severe peel injury on every fruit in the sample. Organoleptic quality attributes of Duncan grapefruit, Temple fruit, and Valencia oranges were evaluated. ollowing irradiation doses of, 1,, and krad, grapefruit were stored at 58 and 65 and Temple fruits were stored at 35 and 5. The storage rooms were maintain ed at relative humidities above 9%. Sections of the stored grapefruit and Temple fruit were presented to the taste panel members for the evaluation of color, texture, and flavor. The juice expressed from the stored Valencia oranges was evaluated for color, consistency, and flavor. A hedonic scale from 1 to 9 was used for the organoleptic ratings: a rating of 1 for dislike extremely and 9 for like extremely. Results and Peel Injury. Effects of irradia tion on decay reduction and on peel injury in Duncan grapefruit are shown in Table 1. Gen erally, storage at low temperature ( ) and the presence of a fungicide (diphenyl) resulted in the reduction of the percent of decayed fruit. However, irradiation did not always reduce de cay. Irradiation induced peel injury which was increased with higher dosages. The severity of peel injury was increased the higher the storage temperature and duration. Irradiated fruit stor ed at had less peel injury in the presence of diphenyl. Definite reduction in the percentages of decay in Pineapple oranges due to radiation were ob tained with the exception of fruit stored at in the presence of diphenyl pads (Table 2). Re- Table 4. Effects of irradiation, storage temperature and duration, and diphenyl on decay (%) and Peel injury (points scale) in Temple fruit. Storaae Temp Period P.I.1/ 1 Dose (krad) P.I Without Diphenyl 1.2 2.6 4. 1.. 6 2. 4. 3 5.8 1.2 2.4 5. 8. 15.8.6 2.3 5. 8 1 9.5 2.5 16. 1. 5 2. 4 35. 4.4 6.8 8.9.1 18..2 32.2 24. With Diphenyl 2.6 1.9 38.. 8 3. 8 56. 2.8 2.9. 4 1. 6 1. 8 2. 9 4. 4 2.5 8.6 2.2 5.1 2.3 8.6 3.4 3.8 1. 2. 1 9. 5..3 2. 5. 18. 5 25..6 4.9 6.8 1. 31. 6.5 18.3 3.3 13.3 23.1 1.,9 24,,5 68,,3 _1/ = peel injury en a point scale. Individual fruits were scored, = none, 1 3 = severe peel injury (1 fruits examined) = slight, 2 = medium and
DENNISON ET AL: IRRIDATION O CITRUS RUIT 289 duction in decay was more apparent with dos ages above 1 krad. Similar reductions of de cayed fruit stored at were obtained with either the addition of fumigant pads on un treated fruit or by radiation with a krad dose. Diphenyl pads had no effect on decay at but irradiated fruits had less decay than control fruit. However, irradiation decreased decay of fruit held at. The amount of decay and the incidence of peel injury increased with the storage temperature and duration. Di phenyl reduced peel injury only with fruits ex posed to to krad and stored at. Irradiation reduced decay for Valencia oranges stored at without diphenyl pads (Table 3). A slight decay reduction due to radiation was obtained when the fungicide was incorporated with the fruit. Control and radi ated fruit stored at exhibited less decay with diphenyl. The severity of peel injury in creased with dose level, storage temperature and duration. This is analogous with radiation ef fects on Duncan grapefruit and Pineapple oranges. The effects of diphenyl on peel injury with irradiated fruit were modified by storage temperature. ruit exhibited less peel injury with diphenyl at while there were no dif ferences at storage, except for the 1 krad treatment. There was no apparent decay reduction due to radiation in Temple fruit (Table 4). Storage at with diphenyl pads was more effective than irradiation for decay reduction. Temple fruit were less susceptible to radiation-induced Table 5. Effects of irradiation, storage temperature and duration on mean organoleptic ratings of Duncan grapefruit sections. Storage Temp. Period s Quality attribute Dose (krad) 1 58 12 8.a.9a.a 6.8a.a 6.a.9a.8a 5. 6b 5. b 2 8.a 8.a 6.9a.a.a 6.9a.9a.8a 6.8a 6.5a 6.4a 6.2a 65 11 8.1a 8.3a.3a.2a 6.8a.a 8.1a 8.3a.a 6.6a 6.2a 19.a.9a 6.8a.a 6.9a 6.2a.8a.a 6.9a 6.8a Means, within groups, followed by the same letter are not statistically different at the 5% level of probability.
29 LORIDA STATE HORTICULTURAL SOCIETY, 1966 peel injury than Pineapple or Valencia oranges with krad was rated less acceptable than (Tables 2, 3, 4). other dosages. However, after 26 s at 35, Organoleptic Evaluation. There were no there were no differences in the flavor ratings differences in the organoleptic attributes among between irradiation levels. the control and irradiated Duncan grapefruit The sections from Temple fruit irradiated sections, with the sole exception of flavor scores with dosages above 1 krad were softer and for dosages above 1 krad when the fruit were less acceptable in flavor when the fruits were stored at 58 for 12 s (Table 5). However, stored for s at 35 or 5 (Table ). With when storage at 58 was extended to 2 s, 13 s storage there were no differences in the there were no differences in the flavor of irradi- flavor of irradiated and non-irradiated fruit ated and control fruit. stored at 5, but fruit irradiated with and There were no differences in color and con- krad and stored at 35 received a lower sistency of the juice expressed from irradiated rating for flavor. With 13 s storage at 35 and non-irradiated fruits (Table 6). The flavor and 5 no changes were apparent in the texof the juice obtained from oranges irradiated ture ratings. Table 6. Effects of irradiation, storage temperatue and duration on the mean organoleptic ratings of the juice expressed from Valencia oranges. S tor acre Quality attribute Dose 1 (krad) 35 12 Consistency. Oa. Oa. Oa.a 6.8a 6.6a.a 6.4a 5.6b.a 6.2a 4.6c 26 Consistency. Oa 6. 9a 5. 9a 6.a 6.8a 5.2a 6.6a 6.2a 4.9a 6.6a 4.6a 5 11 Consistency 5. 9a 6. 8a 6. 2a 6.a 6.a 5.3ab 5.8a 6.5a 5.ab 5.9a 4.8b 19 Consistency. 9a 6. 9a 6. 9a.a 6.a.4a 6.4a 6.a.2a 5.b Means, within groups, followed by the same letter are not statistically different at the 5% level of probability.
1 DENNISON ET AL: IRRIDATION O CITRUS RUIT 291 Discussion inactivation of decay organisms. However, peel injury to lorida citrus fruit was more severe Radiation resulted in some decay reduction as the irradiation dose increased. This is in varin Pineapple and Valencia oranges stored at iance to radiation effects on California navel. The decay reduction was more apparent with oranges (5, 6, ) which may be attributed to dosages above 1 krad. The flux rate and the the nature of the fruit and to the environmental total dose delivered are important parameters conditions during fruit growth in lorida vs. in decay control. The higher the flux rate the California. General observations indicate that lower total dose required for complete decay oranges grown in arid areas are far less subject control. Beraha (1) obtained effective decay to all forms of peel injury than oranges grown control over a dose range of 15 to 182 krad in humid regions (4). It would be desirable to at a flux rate of 2 krad per minute, but with use a dose level where good decay control is krad per minute flux rate, the dose range was obtained with the least possible peel injury to 125 to 13 krad. The dosages used in the present lorida grown citrus fruits. Sommer (8) showstudy were delivered at the rate of 5. krad per ed that by exposure to moist heat some organminute, hence, higher total dosages than used isms can be sensitized so that they can be inin the present study are required for complete activated at.lower irradiation doses. Hot water Table. Effects of irradiation, storage temperature and duration on mean organoleptic ratings of Temple fruit sections. Storage Quality Temp. Period attribute Dose (krad) 1 35 Textur e 9.a.6a.a.9a.3a 6.5a 8.2a 5.4b 5.1b 8.2a 5.5b 4.2b 13.1a.a.9a.1a 6.a 6.8a 6.9a 6.b 5.b.a 5.b 5.2b 5 6.9a 6.a 6.a 6.9a 6.6a 6.8a.a 5.5b 5.b.1a 5.9b 5.4b 13.9a.8a.a.8a.5a 6.9a.a 6.2b.8a 6.5b Means, within groups, followed by the same letter are not statistically different at the 5% level of probability.
292 LORIDA STATE HORTICULTURAL SOCIETY, 1966 treatment of citrus followed by exposure to low irradiation doses may prove beneficial. The organoleptic quality attributes of the ir radiated lorida citrus fruits did not vary sig nificantly from that of control fruits. There were no serious objections from the taste panel members to the quality attributes of irradiated fruits. The lowest rating of the radiated product at the krad dose was 'dislike slightly/ This objectionable rating might be obviated by the use of lower dosages. Results obtained are in accordance with those found for navel oranges (5, 6, ) and grapefruit (2, 1). Acknowledgment This work was supported by USAEC con tract No. At-(-1)-39. ORO-39-5. LITERATURE CITED 1. Beraha, L. 1964. Influence of gamma radiation dose rate on decay of citrus, pears, peaches, and on Penicillium italicum and Botrytis cinerea in vitro. Phytopathology 54: 55-59. 2. Brownell, L. E., L. L. Kempe, J. T. Graikoski, and J. V. Nehemias. 1953. Utilization of the gross fission prod ucts. Engin. Res. Inst. Prog. Rep. No. 5, USAEC AT (11-1)- 162. 3. Brownell, L. E., L. L. Kempe, S. Petersen, H. O. rance, and J. V. Nehemias. 1954. Utilization of the gross fission products. Engin. Res. Inst. Prog. Rep. No. 6 USAEC AT (11-1)-162. 4. Grierson, W., and R. A. Dennison. 1965. Irradiation treatment of Valencia oranges and Marsh grapefruit. Proc. la. State Hort. Soc. 8: 233-23. 5. Guerrero,. P., E. C. Maxie, C. P. Johnson, I. L. Eaks, and N.. Sommer. 1966. Effect of gamma irradia tion on post-harvest behavior of orange fruits. Proc. Amer. Soc. Hort. Sci. In press. 6. Maxie, E. C, N.. Sommer, and I. L. Eaks. 1963. Radiation Technology in conjunction with post-harvest procedures as a means of extending the shelf life of fruits and vegetables. Ann. Rep. USAEC Contract T(lll)3. 34. Maxie, E. C, I. L. Eaks, H. L. Rae, C. Boyd, D. Ravetto, and G. Millay. 1964. Radiation technology in conjunction with post harvest procedures as a means of extending the shelf life of fruits and vegetables. Ann. Rep. USAEC Contract AT (11-1)-34. 8. Sommer, N.. 1966. Ionizing radiation as a means of extending the life of horticultural products. Paper presented at the XVII International Horticultural Con gress, College Park, Maryland. 9. U.S. Dept. of Commerce. 195. Radiation Preserva tion of ood. Ch. 26. U.S. Army Quartermaster Corp, Res. and Dev. Series, Natick, Mass., Pb 1593. 1. U.S. Dept. of Commerce. 1961. Preservation of ood by Low Dose Ionizing Energy. Ch. 4. U.S. Army Quartermaster Corp, Res. and Engin. Center, Natick, Mass. IRRADIATION EECTS ON JUICES EXTRACTED ROM TREATED 'VALENCIA' ORANGES AND 'DUNCAN' GRAPERUIT1 A. H. Rouse2, R. A. Dennison3, and C. D. Atkins4 Abstract Exposure of citrus fruits to gamma radia tions at levels of 15 and krad increased water-soluble pectin from 66 to 488% in extract ed orange juices and from 6 to 2% in grape fruit juices. The higher radiation level always increased the water-soluble pectin the most in juices. Ascorbic acid decreased in the juices from fruit receiving krad. Irradiated fruit stored 3 weeks at usually decreased in ascorbic acid at both levels. Citric acid de creased in juices of irradiated oranges at both lorida Agricultural Experiment Stations Journal Ser ies No. 256. lcooperative research by the lorida Citrus Experiment Station and the lorida Citrus Commission. 2University of lorida Citrus Experiment Station, Lake Alfred. 3Department of ood Science, University of lorida, Gainesville. 4lorida Citrus Commission, Lake Alfred. levels, but usually increased in juices from ir radiated grapefruit. of juices was not in fluenced by low-level gamma irradiation of the fruit. Introduction resh fruit, berries, and vegetables are gam ma irradiated usually to reduce decay incidence, thus extending the keeping quality of these per ishable products. The anticipated increase in shelf-life is not always realized because of the secondary effects of radiation on physical and chemical changes within the plant tissue (5, 9). Some fruits are more susceptable than others to irradiation damage, and Dennison and Ahmed (2) reported in their summation that no single radiation dose can be stated that will be the minimum required to protect citrus fruits against spoilage. Some metabolic processes are accelerated when citrus fruits are irradiated and the rate of acceleration may vary with the dosage level. Dennison et al. (3) have shown that the titrat-