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Interaction of hot water treatments and controlled atmosphere storage on quality of `Fuyu' persimmons
Postharvest Biology and Technology 12 (1997) 71 – 81
Interaction of hot water treatments and controlled atmosphere storage on quality of ‘Fuyu’ persimmons Douglas M. Burmeister *, Sarah Ball, Stephen Green, Allan B. Woolf The Horticulture and Food Research Institute of New Zealand, Mt. Albert Research Centre, Pri6ate Bag 92 169, Auckland, New Zealand Received 26 November 1996; accepted 17 April 1997
Abstract A matrix of 80 hot water treatment (HWT) temperatures/durations and controlled atmosphere (CA) storage regimes were tested for effects on respiratory activity, ethanol (EtOH) and acetaldehyde accumulation (AA), and storage quality of ‘Fuyu’ persimmon. Fruit were hot water treated at 47°C for 45, 60, 90, or 120; min, 50°C for 30, 45, 55, or 60 min; 52°C for 20, 30, 40, or 50 min; 54°C for 15, 20, 25, or 30 min; and as a control treatment, 20°C in air. After treatment, fruit were stored in air, 5% CO2: 2% O2, 10% CO2: 2%, or 100% N2 for 6 weeks at 0°C. Fruit quality was assessed after a 5 day shelf-life at 20°C. Respiration (CO2 production) was measured on fruit held at 20°C following HWT. After storage, C2H4, CO2, EtOH and AA production were measured on selected treatments at 0, 1, 3, and 5 days at 20°C. Hot water treatment alone, or in combination with CA, ameliorated chilling injury (CI). External browning symptoms developed on fruit in some treatments upon removal from storage, severity of symptoms being positively correlated with increasing HWT duration, and most severe in the CA treatments, especially the 100% N2 CA. CO2 production increased after HWT and then decreased (within 24 h), but remained at a higher level than the non-heated control. Following storage, CO2 production rates of fruit from all treatments were relatively similar by the end of the 5 days at 20°C. EtOH and AA production were the greatest in the 100% N2 treatment. Fruit under the longer HWT durations had lower CO2 and C2H4 production after storage and accumulated more EtOH and AA during the 5 day shelf life. These were also the treatments resulting in the lowest levels of CI. Possible mechanisms of HWT and CA alleviation of CI in ‘Fuyu’ persimmon are discussed. © 1997 Elsevier Science B.V. Keywords: Persimmon; Controlled atmosphere; Chilling injury; Hot water treatment
1. Introduction
* Corresponding author. Fax: +64 9 8154201.
Persimmons (Diospyros kaki L. cv. Fuyu) grown under New Zealand conditions are subject
0925-5214/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S 0 9 2 5 - 5 2 1 4 ( 9 7 ) 0 0 0 2 9 - X
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D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
to chilling injury (CI) during postharvest storage. CI is manifest as a gelling of the interior flesh, and its severity may vary between orchards, maturities, and seasons (MacRae, 1987). Over a range of horticultural crops, a variety of postharvest storage and handling procedures are employed to overcome CI (Wang, 1993). Hot water treatments (HWT) have been demonstrated to reduce CI of ‘Fuyu’ persimmon. Results from our unpublished previous work and others (Tanaka et al., 1971) have shown that CI of ‘Fuyu’ persimmon can also be inhibited by CA storage, with the best results obtained with an atmosphere of 100% nitrogen. The objective of this study was to determine if short duration HWT in conjunction with CA storage could be employed to improve the storage life of ‘Fuyu’ persimmons. Because ‘Fuyu’ persimmon can withstand prolonged exposures to 100% N2 atmospheres, we also were interested in the fundamental nature of the response of ‘Fuyu’ to CA and HWT, and the relationship to CI. The following is an examination of the effects of HWT and CA storage on the storage quality and physiology of ‘Fuyu’ persimmons.
bers. Each CA chamber contained all HWT durations for one temperature and was replicated four times. Additional air control consisted of four tray packs held in static air. Treatments were:
20°C air for 120 min (control)
and HWT at: 47°C 50°C 52°C 54°C
for for for for
45, 30, 20, 15,
60, 45, 30, 20,
90 55 40 25
or or or or
120 min 60 min 50 min 30 min
CA chambers were immediately sealed, placed into a refrigerated storage (within 30 min) at 0°C and ventilated with humidified atmospheres of 5% CO2: 2% O2, or 10% CO2: 2% O2 or 100% N2 so that O2 and CO2 concentrations in the chambers were maintained at9 0.2% of ventilation atmospheres. Packets of hydrated lime (Ca(OH)2; 200 g) were included to prevent CO2 accumulation in the 100% N2 treatment. Atmospheres were monitored by sampling the CA chamber headspace with a 1 ml syringe and analysing by gas chromatography.
2.3. Fruit quality assessment 2. Methods
2.1. Fruit source Fruit used were export grade (180 – 220 g) ‘Fuyu’ from a commercial orchard near Auckland, NZ. Fruit were harvested, graded and transported to the Mt Albert Research Centre where they were held overnight at 20°C. Treatments were carried out the following day.
2.2. HWT and storage procedure Fruit were placed in weighted plastic net baskets which each held a replicate of seven fruit. HWT were carried out in water baths as described by Lay–Yee et al. (1997) such that water temperature varied by no more than 0.2°C from the set temperature. After treatment fruit were removed from the basket, towel-dried and placed into 20 l CA cham-
Fruit were removed from refrigerated storage after 6 weeks at 0°C, and fruit quality assessed after 5 days at 20°C. Flesh firmness was measured using an Imada Seisakusyo penetrometer (8 mm diameter conical head) by taking the average of four measurements around the equator of the fruit. The measurements were made directly through the skin surface until the widest point of the cone was reached (MacRae, 1987). Chilling injury in ‘Fuyu’ persimmon is manifest as gelling of the cortical tissue of the fruit. This was assessed by cutting the fruit equatorially and subjectively rating CI on a scale of 0 (no gel) to 5, (firm, dark gel over the entire cut surface; mottled external appearance) as in MacRae (1987). We consider a CI5 2 to be commercially acceptable. The amount of external (skin) browning (EB) was rated on a scale of 0, (no browning) to 3, (browning of over ]75% of the skin).
D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
2.4. Gas analysis Fruit were placed in sealed plastic containers (1 or 2 l) fitted with a septum. Headspace samples were drawn with a 1 ml syringe after 1, 2, or 3 h. O2 was measured using an O2 electrode (Citicell e/s type, City Technology, London, UK) in series with an infrared CO2 transducer (Servomex 1505, Servomex Ltd., Sussex, UK). Ethylene, EtOH, and AA were measured by gas chromatography utilising a Pye Unicam Model PU4500 (Alltech Associates, Auckland, NZ) fitted with a flame ionisation detector.
2.5. Statistical analysis and data presentation Fruit quality data were analysed by analysis of variance partitioning the main effects and interactions into single degrees of freedom (df) to determine sources of variation (Little, 1981). CO2, C2H4, EtOH, and AA data were analysed and are presented using a ln(X) or ln(X +1) non-linear transformation. The interaction of HWT and storage atmosphere on CI and EB are presented as three-dimensional histograms. The histograms vary slightly in aspect to better display the interaction of CA and HWT for each temperature.
3. Results and discussion
3.1. Fruit quality In general, either HWT or CA ameliorated CI in comparison to air control. All HWT temperature, duration and atmosphere effects and interactions on quality parameters measured were significant at P ] 0.001. The differences between 10% CO2: 2% O2 and 5% CO2: 2% O2 were not significant, and thus only the data for the 10% CO2: 2% O2 treatment is presented. The main effects of CA alone without HWT were not significant. Shorter durations of HWT were required to control CI with increasing HWT temperature (Fig. 1). This duration/temperature interaction is consistent with previous work with persimmon (Lay –Yee et al., 1997), and other fruit species (Klein and Lurie, 1992; Woolf et al., 1995). Most
73
54°C HWT/CA treatments resulted in unacceptable CI levels (Fig. 1d). In the 47°C, 50°C, and 52°C HWT temperatures, there was a synergistic effect of CA and HWT, with some combinations alleviating CI over HWT or CA alone (Fig. 1a– c). This attenuation of CI was paralleled by maintained fruit firmness and higher juiciness (data not shown). Under the conditions employed in this experiment, storage under 100% N2 without HWT did not satisfactorily control chilling injury or maintain flesh firmness. This differed from unpublished from our laboratory results in the same season and over the previous 3 years. One factor that could account for this difference is the wetting of the fruit during HWT. Even though fruit were carefully dried following HWT, when they were placed (still warm) into refrigerated storage moisture would condense on the fruit surface. At the same time containers were being ventilated with a high humidity atmosphere. Thus, humidity conditions in the container were likely to be very high minimising water loss which could increase CI. This is consistent with the suggestion that high water loss early in storage may reduce the development of CI in various fruit species (Forney and Lipton, 1990). The severity of EB symptoms was positively correlated with increasing HWT duration, and was generally more severe when fruit were stored under 100% N2 or longer duration HWTs at 47°C (Fig. 2). The fruit appeared to be in good condition when removed from storage, but developed EB symptoms during 5 days at 20°C. ‘Fuyu’ persimmon have been noted to be susceptible to skin discolouration during storage (Yamamura et al., 1984). Lee et al. (1993) examined browning during storage of ‘Fuyu’ persimmon and found that it was greater in immature fruit, and where orchard soil was higher in nitrogen. The browning was partially controlled by the antioxidant diphenylamine (DPA) and by CA storage, but the authors gave no indication of the time during shelf life at which fruit were examined. Wetting fruit during HWT may be the cause of EB because it has been demonstrated that EB on ‘Fuyu’ is positively correlated with moisture content of fruit skin and increased by water sprays at harvest
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Fig. 1. Interaction of CA and HWT on development of chilling injury. Histograms are the mean of four replicates of seven fruit. LSD= 1.2.
(Kim et al., 1989). We have not observed any EB in three previous seasons’ work. Therefore, susceptibility to EB may relate to preharvest factors such as seasonal weather conditions, maturity and/or other orchard factors. We have also determined that application of 1 mg l − 1 DPA upon removal from storage gives partial attenuation of EB indicating that an oxidative process may be involved. The fact that fruit are apparently sound upon removal from storage and develop the symptoms upon warming is symptomatic of many browning disorders such as superficial scald in apple (Ingle and D’Souza, 1989).
3.2. CO2 production during HWT and following storage Immediately following HWT, CO2 production was higher and then decreased to a level above the non-heated control within 24 h (Fig. 3). We conducted three similar experiments during this season utilising various HWT temperatures and durations with similar results (data not presented). For fruit studied following storage, the main effects of atmosphere, HWT temperature and duration were significant at P5 0.001 accounting for 94% of the variation in CO2 production. Upon
D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
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Fig. 2. Interaction of CA and HWT on development of external browning symptoms. Histograms are the mean of four replicates of seven fruit. LSD = 0.6.
transfer to 20°C, CO2 production declined in all treatments. By the end of the 5 days at 20°C, CO2 production rates were relatively similar (Fig. 4). During shelf life, there was a tendency for the longer HWT durations to have lower respiration rates (Fig. 4). These were also the treatments which reduced CI, consistent with the observations of MacRae (1987) in which higher respiration rates were associated with increased CI.
3.3. C2H4 production following storage The main effects of atmosphere, HWT temperature and HWT duration were significant at P 5 0.001 accounting for 12, 26 and 53% of the variation in C2H4 production, respectively.
Ethylene production after storage was inversely related to duration of HWT. Within each HWT temperature, C2H4 production in the longer duration HWT remained lower than the no HWT control until at least 3 days at 20°C (Fig. 5). The exception to this was the 54°C HWT which had greater CI than the other HWT temperatures (Fig. 5). A specific role for C2H4 in CI has not been established (Wang, 1993), but higher C2H4 production rates 1 day after removal from storage have also been associated with increased CI in ‘Fuyu’ persimmon (MacRae, 1987). In response to hot air treatments on ‘Fuyu’, we have also observed reduced C2H4 production 1 day after storage which was correlated with reduced CI (Woolf et al., 1997a,b).
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3.4. EtOH and AA production following storage Statistical analysis of EtOH and AA production following CA storage revealed significant main effects of atmosphere and HWT duration that accounted for 90 and 91% of the variation in EtOH and AA production, respectively. EtOH and AA production were the greatest in the 100% N2 treatment (Fig. 6 and Fig. 7). Also within each HWT temperature fruit subjected to a longer HWT duration prior to storage tended to accumulate and produce more EtOH and AA during the 5 day shelf life. These are also the treatments that developed the least CI. 4. Discussion The mechanisms by which CA and HWT reduce chilling injury are unknown. Saltveit (1994) discovered that exposure of excised cucumber cotyledons and seedling leaves to EtOH vapours or anoxic atmospheres conferred chilling tolerance. He attributed this to the anaesthetic properties of alcohols preventing the phase transition of membranes,
and effects on stomatal closure, thereby preventing water loss normally associated with chilling injury. He suggested EtOH accumulation is the mechanism by which CA attenuates chilling injury. Our experiments did not directly test, but support this hypothesis since the treatments with the least CI also accumulated the most EtOH. Another possible mechanism by which heat treatments (HTs) reduce chilling injury during storage is that of induction of heat shock proteins (hsps) (Vierling, 1991). Such a role has been proposed for cucumber cotyledons (Lafuente et al., 1991), and fruit of avocado (Woolf et al., 1995) and tomato (Lurie and Klein, 1991). However, in these systems, effective HTs occur at lower temperatures (38–40°C) where hsp induction is highest (Woolf et al., 1995). Indeed, induction of some specific hsps may be significantly reduced at ] 42°C (Woolf et al., 1995; Ferguson et al., 1994). For persimmons, hot air HTs most effective at reducing chilling injury where \ 45°C while 38°C treatments had no effect on chilling injury during storage (Woolf et al., 1997a). The possible involvement of hsps in persimmon low temperature tolerance remains to be investigated. A further explanation for chilling-tolerance is that these temperatures result in changes in the activity of cell wall degrading enzymes and/or the cell wall itself. For example, Woolf et al. (1997b) have demonstrated that hot air HTs prior to storage inhibit the release of high molecular mass hydrophilic pectin from the cell wall which was associated with development of chilling injury. Such changes are also likely to occur in response to HWTs. 5. Conclusions
Fig. 3. Carbon dioxide production at 20°C following HWT. Data points are the mean of ten individual fruit replicates 9 standard error of the mean.
We have presented data regarding the response of ‘Fuyu’ to HWT and CA. HWT alone or in conjunction with CA has potential as a storage technique. The limiting factor seems to be the external browning symptoms that can develop during shelf life of the fruit. We are intrigued by the apparent tolerance of ‘Fuyu’ to long-term exposures to 100% N2 atmospheres and believe that it may be useful as a model to investigate the underlying physiology and biochemistry of fruit response to HWT and CA.
D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
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Fig. 4. Carbon dioxide production of hot water treated/CA stored fruit during 5 days at 20°C following 6 weeks 0°C storage. Data were analysed and presented as ln(mmoles CO2 kg − 1 h − 1)9 standard error of the mean. Each data point is the mean of four replicates of seven fruit.
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D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
Fig. 5. Ethylene production of hot water treated/CA stored fruit during 5 days at 20°C following 6 weeks 0°C storage. Data were analysed and presented as ln(mmoles C2H4 kg − 1 h − 1)9 standard error of the mean. Each data point is the mean of four replicates of seven fruit.
D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
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Fig. 6. Ethanol production of hot water treated/CA stored fruit during 5 days at 20°C following 6 weeks 0°C storage. Data were analysed and presented as ln(mmoles EtOH kg − 1 h − 1)9 standard error of the mean. Each data point is the mean of four replicates of seven fruit.
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D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
Fig. 7. Acetaldehyde production of hot water treated/CA stored fruit during 5 days at 20°C following 6 weeks 0°C storage. Data were analysed and presented as ln((nmoles AA + 1) kg − 1 h − 1) 9standard error of the mean. Each data point is the mean of four replicates of seven fruit.
D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
Acknowledgements Thanks are extended to Peter and Liz Hedley for supplying us with the fruit and to Michael Lay –Yee for initial discussions. To John Elgar and Ian Ferguson for editing and comments on this manuscript and Marcus Davy for the statistical analyses.
References Ferguson, I.B., Lurie, S., Bowen, J.H., 1994. Protein synthesis and breakdown during heat shock of cultured pear (Pyrus communis L.) cells. Plant Physiol. 104, 1429–1437. Forney, C.F., Lipton, W.J. 1990. Influence of Controlled Atmospheres and packaging on chilling sensitivity. In: Wang C.Y. (Ed.), Chilling Injury of Horticultural Crops. CRC Press, Boca Raton, pp. 145–164. Ingle, M., D’Souza, M.C., 1989. Physiology and control of superficial scald of apples: A review. HortScience 24, 28– 31. Kim, Y.S., Jeong, S., Son, D., Lee, K., Lee, U., 1989. Studies on the casual factors of skin browning during storage and its control method in non–astringent persimmon (Diospryros Kaki Thumb.). Korean Rural Dev. Adm. Rep. (H) 31 (3), 62 – 72. Klein, J.D., Lurie, S., 1992. Prestorage heating of apple fruit for enhanced postharvest quality: Interaction of time and temperature. HortScience 27, 326–328. Lafuente, M.T., Belver, A., Guye, M.G., Saltveit, M.E., 1991. Effect of temperature conditioning on chilling injury of cucumber cotyledons. Plant Physiol. 95, 443–449. Lay–Yee, M., Ball, S., Forbes, S.K., Woolf, A.B., 1997. Hot water treatment for insect disinfestation and reduction of chilling sensitivity of Fuyu persimmon. Postharvest Biol. Tech. 10 (1), 81 – 87. Lee, S.K., Shin, I.S., Park, Y.M., 1993. Factors involved in skin browning of non-astringent Fuyu persimmon. Acta Hort. 343, 300 – 303.
.
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Little, T.M., 1981. Interpretation and presentation of results. Proceedings of the Symposium, Statistics: A tool for the horticultural scientist. HortScience 16, 262 – 266. Lurie, S., Klein, J.D., 1991. Acquisition of low-temperature tolerance in tomatoes by exposure to high temperature stress. J. Am. Soc. Hort. Sci. 116, 1007 – 1012. MacRae, E.A., 1987. Development of chilling injury in New Zealand grown ‘Fuyu’ persimmon during storage. N. Z. J. Exp. Agric. 15, 333 – 344. Saltveit, M.E., 1994. Exposure to alcohol vapours reduces chilling-induced injury of excised cucumber cotyledons, but not of seedlings or excised hypocotyl segments. J. Exp. Bot. 45, 813 – 821. Tanaka, Y., Takase, N., Sato, J., 1971. Studies on the CAstorage of fruits and vegetables, III. Effect of CA-storage on the quality of persimmons (Diospyros kaki LINN.f.). Res. Bull. Aichi Prefecture Agric. Res. Center, Series B, c 3. Vierling, E., 1991. The roles of heat shock proteins in plants. Annu. Rev. Plant Phys. Mol. Biol. 42, 579 – 620. Wang, C.Y., 1993. Approaches to reduce chilling of fruits and vegetables. In: Jules Janick (Ed.), Horticultural Reviews. Wiley, New York, 15, pp. 63 – 86. Woolf, A.B., Watkins, C.B., Bowen, J.H., Lay – Yee, M., Maindonald, J.H., Ferguson, I.B., 1995. Reduction of external chilling injury in stored ‘Hass’ avocado fruit by dry heat treatments. J. Am. Soc. Hort. Sci. 120, 1050 – 1056. Woolf, A.B., Spooner, K.J., Lay – Yee, M., Ferguson, I.B., Watkins, C.B., Forbes, S.K., 1997a. Reduction of chilling injury in the sweet persimmon ‘Fuyu’ by hot air heat treatments. Postharvest Biol. Tech in press. Woolf, A.B., MacRae, E.A., Spooner, K.J., Redgwell, R.J., 1997b. Changes to physical properties of the cell wall and polyuronides in response to heat treatments of ‘Fuyu’ persimmon which alleviate chilling injury. J. Am. Soc. Hort. Sci. in press. Yamamura, H., Bessho, H., Naito, R., 1984. Occurrence of black stain on fruit skin (black spots) in relation to growth and development of pericarp tissues in Japanese persimmon. J. Jpn. Soc. Hort. Sci. 53, 115 – 120.
Interaction of hot water treatments and controlled atmosphere storage on quality of ‘Fuyu’ persimmons Douglas M. Burmeister *, Sarah Ball, Stephen Green, Allan B. Woolf The Horticulture and Food Research Institute of New Zealand, Mt. Albert Research Centre, Pri6ate Bag 92 169, Auckland, New Zealand Received 26 November 1996; accepted 17 April 1997
Abstract A matrix of 80 hot water treatment (HWT) temperatures/durations and controlled atmosphere (CA) storage regimes were tested for effects on respiratory activity, ethanol (EtOH) and acetaldehyde accumulation (AA), and storage quality of ‘Fuyu’ persimmon. Fruit were hot water treated at 47°C for 45, 60, 90, or 120; min, 50°C for 30, 45, 55, or 60 min; 52°C for 20, 30, 40, or 50 min; 54°C for 15, 20, 25, or 30 min; and as a control treatment, 20°C in air. After treatment, fruit were stored in air, 5% CO2: 2% O2, 10% CO2: 2%, or 100% N2 for 6 weeks at 0°C. Fruit quality was assessed after a 5 day shelf-life at 20°C. Respiration (CO2 production) was measured on fruit held at 20°C following HWT. After storage, C2H4, CO2, EtOH and AA production were measured on selected treatments at 0, 1, 3, and 5 days at 20°C. Hot water treatment alone, or in combination with CA, ameliorated chilling injury (CI). External browning symptoms developed on fruit in some treatments upon removal from storage, severity of symptoms being positively correlated with increasing HWT duration, and most severe in the CA treatments, especially the 100% N2 CA. CO2 production increased after HWT and then decreased (within 24 h), but remained at a higher level than the non-heated control. Following storage, CO2 production rates of fruit from all treatments were relatively similar by the end of the 5 days at 20°C. EtOH and AA production were the greatest in the 100% N2 treatment. Fruit under the longer HWT durations had lower CO2 and C2H4 production after storage and accumulated more EtOH and AA during the 5 day shelf life. These were also the treatments resulting in the lowest levels of CI. Possible mechanisms of HWT and CA alleviation of CI in ‘Fuyu’ persimmon are discussed. © 1997 Elsevier Science B.V. Keywords: Persimmon; Controlled atmosphere; Chilling injury; Hot water treatment
1. Introduction
* Corresponding author. Fax: +64 9 8154201.
Persimmons (Diospyros kaki L. cv. Fuyu) grown under New Zealand conditions are subject
0925-5214/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S 0 9 2 5 - 5 2 1 4 ( 9 7 ) 0 0 0 2 9 - X
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D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
to chilling injury (CI) during postharvest storage. CI is manifest as a gelling of the interior flesh, and its severity may vary between orchards, maturities, and seasons (MacRae, 1987). Over a range of horticultural crops, a variety of postharvest storage and handling procedures are employed to overcome CI (Wang, 1993). Hot water treatments (HWT) have been demonstrated to reduce CI of ‘Fuyu’ persimmon. Results from our unpublished previous work and others (Tanaka et al., 1971) have shown that CI of ‘Fuyu’ persimmon can also be inhibited by CA storage, with the best results obtained with an atmosphere of 100% nitrogen. The objective of this study was to determine if short duration HWT in conjunction with CA storage could be employed to improve the storage life of ‘Fuyu’ persimmons. Because ‘Fuyu’ persimmon can withstand prolonged exposures to 100% N2 atmospheres, we also were interested in the fundamental nature of the response of ‘Fuyu’ to CA and HWT, and the relationship to CI. The following is an examination of the effects of HWT and CA storage on the storage quality and physiology of ‘Fuyu’ persimmons.
bers. Each CA chamber contained all HWT durations for one temperature and was replicated four times. Additional air control consisted of four tray packs held in static air. Treatments were:
20°C air for 120 min (control)
and HWT at: 47°C 50°C 52°C 54°C
for for for for
45, 30, 20, 15,
60, 45, 30, 20,
90 55 40 25
or or or or
120 min 60 min 50 min 30 min
CA chambers were immediately sealed, placed into a refrigerated storage (within 30 min) at 0°C and ventilated with humidified atmospheres of 5% CO2: 2% O2, or 10% CO2: 2% O2 or 100% N2 so that O2 and CO2 concentrations in the chambers were maintained at9 0.2% of ventilation atmospheres. Packets of hydrated lime (Ca(OH)2; 200 g) were included to prevent CO2 accumulation in the 100% N2 treatment. Atmospheres were monitored by sampling the CA chamber headspace with a 1 ml syringe and analysing by gas chromatography.
2.3. Fruit quality assessment 2. Methods
2.1. Fruit source Fruit used were export grade (180 – 220 g) ‘Fuyu’ from a commercial orchard near Auckland, NZ. Fruit were harvested, graded and transported to the Mt Albert Research Centre where they were held overnight at 20°C. Treatments were carried out the following day.
2.2. HWT and storage procedure Fruit were placed in weighted plastic net baskets which each held a replicate of seven fruit. HWT were carried out in water baths as described by Lay–Yee et al. (1997) such that water temperature varied by no more than 0.2°C from the set temperature. After treatment fruit were removed from the basket, towel-dried and placed into 20 l CA cham-
Fruit were removed from refrigerated storage after 6 weeks at 0°C, and fruit quality assessed after 5 days at 20°C. Flesh firmness was measured using an Imada Seisakusyo penetrometer (8 mm diameter conical head) by taking the average of four measurements around the equator of the fruit. The measurements were made directly through the skin surface until the widest point of the cone was reached (MacRae, 1987). Chilling injury in ‘Fuyu’ persimmon is manifest as gelling of the cortical tissue of the fruit. This was assessed by cutting the fruit equatorially and subjectively rating CI on a scale of 0 (no gel) to 5, (firm, dark gel over the entire cut surface; mottled external appearance) as in MacRae (1987). We consider a CI5 2 to be commercially acceptable. The amount of external (skin) browning (EB) was rated on a scale of 0, (no browning) to 3, (browning of over ]75% of the skin).
D.M. Burmeister et al. / Posthar6est Biology and Technology 12 (1997) 71–81
2.4. Gas analysis Fruit were placed in sealed plastic containers (1 or 2 l) fitted with a septum. Headspace samples were drawn with a 1 ml syringe after 1, 2, or 3 h. O2 was measured using an O2 electrode (Citicell e/s type, City Technology, London, UK) in series with an infrared CO2 transducer (Servomex 1505, Servomex Ltd., Sussex, UK). Ethylene, EtOH, and AA were measured by gas chromatography utilising a Pye Unicam Model PU4500 (Alltech Associates, Auckland, NZ) fitted with a flame ionisation detector.
2.5. Statistical analysis and data presentation Fruit quality data were analysed by analysis of variance partitioning the main effects and interactions into single degrees of freedom (df) to determine sources of variation (Little, 1981). CO2, C2H4, EtOH, and AA data were analysed and are presented using a ln(X) or ln(X +1) non-linear transformation. The interaction of HWT and storage atmosphere on CI and EB are presented as three-dimensional histograms. The histograms vary slightly in aspect to better display the interaction of CA and HWT for each temperature.
3. Results and discussion
3.1. Fruit quality In general, either HWT or CA ameliorated CI in comparison to air control. All HWT temperature, duration and atmosphere effects and interactions on quality parameters measured were significant at P ] 0.001. The differences between 10% CO2: 2% O2 and 5% CO2: 2% O2 were not significant, and thus only the data for the 10% CO2: 2% O2 treatment is presented. The main effects of CA alone without HWT were not significant. Shorter durations of HWT were required to control CI with increasing HWT temperature (Fig. 1). This duration/temperature interaction is consistent with previous work with persimmon (Lay –Yee et al., 1997), and other fruit species (Klein and Lurie, 1992; Woolf et al., 1995). Most
73
54°C HWT/CA treatments resulted in unacceptable CI levels (Fig. 1d). In the 47°C, 50°C, and 52°C HWT temperatures, there was a synergistic effect of CA and HWT, with some combinations alleviating CI over HWT or CA alone (Fig. 1a– c). This attenuation of CI was paralleled by maintained fruit firmness and higher juiciness (data not shown). Under the conditions employed in this experiment, storage under 100% N2 without HWT did not satisfactorily control chilling injury or maintain flesh firmness. This differed from unpublished from our laboratory results in the same season and over the previous 3 years. One factor that could account for this difference is the wetting of the fruit during HWT. Even though fruit were carefully dried following HWT, when they were placed (still warm) into refrigerated storage moisture would condense on the fruit surface. At the same time containers were being ventilated with a high humidity atmosphere. Thus, humidity conditions in the container were likely to be very high minimising water loss which could increase CI. This is consistent with the suggestion that high water loss early in storage may reduce the development of CI in various fruit species (Forney and Lipton, 1990). The severity of EB symptoms was positively correlated with increasing HWT duration, and was generally more severe when fruit were stored under 100% N2 or longer duration HWTs at 47°C (Fig. 2). The fruit appeared to be in good condition when removed from storage, but developed EB symptoms during 5 days at 20°C. ‘Fuyu’ persimmon have been noted to be susceptible to skin discolouration during storage (Yamamura et al., 1984). Lee et al. (1993) examined browning during storage of ‘Fuyu’ persimmon and found that it was greater in immature fruit, and where orchard soil was higher in nitrogen. The browning was partially controlled by the antioxidant diphenylamine (DPA) and by CA storage, but the authors gave no indication of the time during shelf life at which fruit were examined. Wetting fruit during HWT may be the cause of EB because it has been demonstrated that EB on ‘Fuyu’ is positively correlated with moisture content of fruit skin and increased by water sprays at harvest
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Fig. 1. Interaction of CA and HWT on development of chilling injury. Histograms are the mean of four replicates of seven fruit. LSD= 1.2.
(Kim et al., 1989). We have not observed any EB in three previous seasons’ work. Therefore, susceptibility to EB may relate to preharvest factors such as seasonal weather conditions, maturity and/or other orchard factors. We have also determined that application of 1 mg l − 1 DPA upon removal from storage gives partial attenuation of EB indicating that an oxidative process may be involved. The fact that fruit are apparently sound upon removal from storage and develop the symptoms upon warming is symptomatic of many browning disorders such as superficial scald in apple (Ingle and D’Souza, 1989).
3.2. CO2 production during HWT and following storage Immediately following HWT, CO2 production was higher and then decreased to a level above the non-heated control within 24 h (Fig. 3). We conducted three similar experiments during this season utilising various HWT temperatures and durations with similar results (data not presented). For fruit studied following storage, the main effects of atmosphere, HWT temperature and duration were significant at P5 0.001 accounting for 94% of the variation in CO2 production. Upon
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Fig. 2. Interaction of CA and HWT on development of external browning symptoms. Histograms are the mean of four replicates of seven fruit. LSD = 0.6.
transfer to 20°C, CO2 production declined in all treatments. By the end of the 5 days at 20°C, CO2 production rates were relatively similar (Fig. 4). During shelf life, there was a tendency for the longer HWT durations to have lower respiration rates (Fig. 4). These were also the treatments which reduced CI, consistent with the observations of MacRae (1987) in which higher respiration rates were associated with increased CI.
3.3. C2H4 production following storage The main effects of atmosphere, HWT temperature and HWT duration were significant at P 5 0.001 accounting for 12, 26 and 53% of the variation in C2H4 production, respectively.
Ethylene production after storage was inversely related to duration of HWT. Within each HWT temperature, C2H4 production in the longer duration HWT remained lower than the no HWT control until at least 3 days at 20°C (Fig. 5). The exception to this was the 54°C HWT which had greater CI than the other HWT temperatures (Fig. 5). A specific role for C2H4 in CI has not been established (Wang, 1993), but higher C2H4 production rates 1 day after removal from storage have also been associated with increased CI in ‘Fuyu’ persimmon (MacRae, 1987). In response to hot air treatments on ‘Fuyu’, we have also observed reduced C2H4 production 1 day after storage which was correlated with reduced CI (Woolf et al., 1997a,b).
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3.4. EtOH and AA production following storage Statistical analysis of EtOH and AA production following CA storage revealed significant main effects of atmosphere and HWT duration that accounted for 90 and 91% of the variation in EtOH and AA production, respectively. EtOH and AA production were the greatest in the 100% N2 treatment (Fig. 6 and Fig. 7). Also within each HWT temperature fruit subjected to a longer HWT duration prior to storage tended to accumulate and produce more EtOH and AA during the 5 day shelf life. These are also the treatments that developed the least CI. 4. Discussion The mechanisms by which CA and HWT reduce chilling injury are unknown. Saltveit (1994) discovered that exposure of excised cucumber cotyledons and seedling leaves to EtOH vapours or anoxic atmospheres conferred chilling tolerance. He attributed this to the anaesthetic properties of alcohols preventing the phase transition of membranes,
and effects on stomatal closure, thereby preventing water loss normally associated with chilling injury. He suggested EtOH accumulation is the mechanism by which CA attenuates chilling injury. Our experiments did not directly test, but support this hypothesis since the treatments with the least CI also accumulated the most EtOH. Another possible mechanism by which heat treatments (HTs) reduce chilling injury during storage is that of induction of heat shock proteins (hsps) (Vierling, 1991). Such a role has been proposed for cucumber cotyledons (Lafuente et al., 1991), and fruit of avocado (Woolf et al., 1995) and tomato (Lurie and Klein, 1991). However, in these systems, effective HTs occur at lower temperatures (38–40°C) where hsp induction is highest (Woolf et al., 1995). Indeed, induction of some specific hsps may be significantly reduced at ] 42°C (Woolf et al., 1995; Ferguson et al., 1994). For persimmons, hot air HTs most effective at reducing chilling injury where \ 45°C while 38°C treatments had no effect on chilling injury during storage (Woolf et al., 1997a). The possible involvement of hsps in persimmon low temperature tolerance remains to be investigated. A further explanation for chilling-tolerance is that these temperatures result in changes in the activity of cell wall degrading enzymes and/or the cell wall itself. For example, Woolf et al. (1997b) have demonstrated that hot air HTs prior to storage inhibit the release of high molecular mass hydrophilic pectin from the cell wall which was associated with development of chilling injury. Such changes are also likely to occur in response to HWTs. 5. Conclusions
Fig. 3. Carbon dioxide production at 20°C following HWT. Data points are the mean of ten individual fruit replicates 9 standard error of the mean.
We have presented data regarding the response of ‘Fuyu’ to HWT and CA. HWT alone or in conjunction with CA has potential as a storage technique. The limiting factor seems to be the external browning symptoms that can develop during shelf life of the fruit. We are intrigued by the apparent tolerance of ‘Fuyu’ to long-term exposures to 100% N2 atmospheres and believe that it may be useful as a model to investigate the underlying physiology and biochemistry of fruit response to HWT and CA.
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Fig. 4. Carbon dioxide production of hot water treated/CA stored fruit during 5 days at 20°C following 6 weeks 0°C storage. Data were analysed and presented as ln(mmoles CO2 kg − 1 h − 1)9 standard error of the mean. Each data point is the mean of four replicates of seven fruit.
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Fig. 5. Ethylene production of hot water treated/CA stored fruit during 5 days at 20°C following 6 weeks 0°C storage. Data were analysed and presented as ln(mmoles C2H4 kg − 1 h − 1)9 standard error of the mean. Each data point is the mean of four replicates of seven fruit.
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Fig. 6. Ethanol production of hot water treated/CA stored fruit during 5 days at 20°C following 6 weeks 0°C storage. Data were analysed and presented as ln(mmoles EtOH kg − 1 h − 1)9 standard error of the mean. Each data point is the mean of four replicates of seven fruit.
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Fig. 7. Acetaldehyde production of hot water treated/CA stored fruit during 5 days at 20°C following 6 weeks 0°C storage. Data were analysed and presented as ln((nmoles AA + 1) kg − 1 h − 1) 9standard error of the mean. Each data point is the mean of four replicates of seven fruit.
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Acknowledgements Thanks are extended to Peter and Liz Hedley for supplying us with the fruit and to Michael Lay –Yee for initial discussions. To John Elgar and Ian Ferguson for editing and comments on this manuscript and Marcus Davy for the statistical analyses.
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