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Reflective tarps at harvest reduce stem browning and improve fruit quality of cherries during subsequent storage
Postharvest Biology and Technology 25 (2002) 117– 121 www.elsevier.com/locate/postharvbio
Short communication
Reflective tarps at harvest reduce stem browning and improve fruit quality of cherries during subsequent storage Joanne L. Schick, Peter M.A. Toivonen * Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland Research Centre, Summerland, BC, Canada V 0H 1Z0 Received 7 November 2000; accepted 23 June 2001
Abstract The use of a reflective tarp, previously used in forestry, was assessed for its potential to improve the quality retention of sweet cherries (Prunus a6ium L.). The tarp was applied as a cover to bins of harvested cherries in the orchard and also during open-truck transport to the packing house. Controls were bins left uncovered in the orchard and during transport. Harvesting took place in 8-year-old orchards of ‘Lapins’ cherries where the foliar canopy provided very little shade. The results show that the use of reflective tarps can improve the retention of sweet cherry quality when subsequently stored in MAP bags for several weeks. Crown Copyright © 2002 Published by Elsevier Science B.V. All rights reserved. Keywords: Prunus a6ium L.; Postharvest handling; Temperature; Humidity; Modified atmosphere packaging; Reflective (laminated Mylar) film
1. Introduction Stem browning continues to be a problem for sweet cherry marketing in British Columbia, Canada and Washington State, USA (Haas, 1996; Thompson et al., 1997). Temperature and humidity are two factors that have been implicated in stem browning of sweet cherries (Dewey, 1951; Siegelman, 1952). After harvest, both heat from the sun and heat of respiration from the cherry fruit contribute to heat loading of the cherries (Young and Kupferman, 1994). Maintaining
Centre Contribution Number 2100. * Corresponding author. Tel.: +1-250-494-6386; fax: + 1250-494-0755. E-mail address: [email protected] (P.M.A. Toivonen).
lower fruit temperatures immediately after harvest results in firmer fruit with reduced decay and greener stems (Drake et al., 1988; Young and Kupferman, 1994). The optimum relative humidity for storage of sweet cherries has been reported to be between 90 and 95% (Hevia et al., 1998). Relative humidity in this range is particularly important in maintaining green stem color. Water evaporates much more quickly from cherry stems than from the fruit (Seske, 1996) and dessication is generally related to stem browning (Drake et al., 1988). It is clear that deterioration in fruit and stem quality can occur rapidly and therefore improved strategies to moderate both temperature and humidity immediately after harvest should be developed.
0925-5214/02/$ - see front matter. Crown Copyright © 2002 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 5 2 1 4 ( 0 1 ) 0 0 1 4 5 - 4
118
J.L. Schick, P.M.A. Toi6onen / Posthar6est Biology and Technology 25 (2002) 117–121
Reflective materials have been used during reforestation to protect seedlings from heat stress (DeYoe et al., 1985). These tarps are constructed of a Mylar® material sandwiched between a white painted surface and a shiny silver metallic surface. The reflective tarps have been shown to maintain temperature of seedlings equivalent to that of deep shade. They are easy to use and provide a useful tool for forest tree replanting projects in remote areas where refrigeration is unavailable. It was hypothesized that this reflective material could have beneficial effects when used to protect commercially harvested fresh fruit crops. The objectives of this work were: (1) to determine if the use of reflective tarps during harvest and transport could reduce cherry fruit temperature and maintain relative humidity around the fruit; and (2) to determine if the use of reflective tarps is beneficial to subsequent cherry quality during storage in plastic film packages.
2. Materials and methods
2.1. Experimental Reflective tarps (Silvicool III, lightweight) were supplied by Bushpro Supplies (668 Irish Creek Road, Vernon, BC). This reflective tarp is of laminated construction, consisting of a woven polyester core which is double coated with bright white on the outer surface and a silvered Mylar® on the under surface. The tarps were used with the white side facing the sun and the shiny metallic silver surface facing the fruit as this orientation has been shown to be the most effective in preventing heat stress when used on seedlings in reforestation. (DeYoe et al., 1985). Fruit temperature during harvest and transport was measured by miniature temperature/humidity data loggers (model H8, Onset computer Corporation, Pocasset, MA). An extendable temperature sensor was inserted inside the cherry fruit and the loggers were placed into the middle of the bins. The data loggers were placed so they also recorded the relative humidity in the airspace immediately surrounding the cherries. The air temperature and relative humidity within the tree
canopy in the orchard were monitored using the same type of data loggers and these were protected from direct sun exposure by a tent cover which was constructed out of plain white cardboard. This experiment was set up in a commercial orchard of 8-year-old ‘Lapins’ cherry trees on July 15, 1998 beginning at 09:00 h. The average ambient air temperature within the tree canopy during the test was 24.99 0.5 °C, while the average ambient humidity was 339 1%. Three pairs of bins were selected randomly in the orchard during a commercial harvest. Pickers filled a bin within approximately 20 min. One bin of each pair was covered with a reflective tarp and one bin was left as an uncovered control. After filling, the bins remained in the orchard between the tree rows for 4 h, as per practice in that orchard. The bins were then transported on an open flatbed trailer to the packing house in Naramata, British Columbia. The cherries were room-cooled overnight and the following morning they were delivered by a refrigerated truck to the cherry packing facility. Cherry samples were randomly selected from the top, middle and bottom layer of each of the experimental bins and packaged in 1 kg styrene ‘clamshell’ trays. All samples were transported by refrigerated truck to Pacific Agri-Food Research Centre at Summerland, British Columbia. The filled ‘clamshell’ trays were sealed in bags of a polyolefin film (PD-941, Cryovac, Duncan, SC) and stored at 1 °C, 75% RH. This film does not allow significant atmospheric modification, but does maintain a high humidity around the fruit. The atmospheres measured in the bags averaged at 0.7% CO2 and 19.42% O2 during storage. The quality of the cherries was evaluated the next day (i.e. week 0) on one set of samples and subsequently at week 2 and 4 of storage on other sets of samples.
2.2. Quality e6aluations Twenty-five randomly selected fruit from each tray were scored for pitting and decay. Fruit decay was assessed as a percent of fruit from a 25 fruit sample showing any type of decay, however,
J.L. Schick, P.M.A. Toi6onen / Posthar6est Biology and Technology 25 (2002) 117–121
the decay organisms were not identified. Pitting was evaluated and recorded as a percentage of 25 fruit showing visible pitting. The stems of the fruit were rated for color using a four point index: 4=0 – 25% of the stem surface being brown, 3 = 25 – 50% of the surface being brown, 2 =50 –75% of the surface being brown and 1 =75 –100% of the surface being brown. The stems were then weighed and dried at 60 °C in a vacuum oven for 24 h and then reweighed. The percentage water content of the stems were calculated using the initial (fresh) and final (dry) weights.
2.3. UV-absorbing solute leakage measurements Tissue leakage of the stems was determined using the method described by Redman et al. (1986). Ten stems were cut with a razor blade into sections of 1 mm length and leakage determined over a two hour incubation at room temperature by measuring absorbance of the bathing medium at 280 nm. The samples were then frozen at − 20 °C, thawed and a second absorbance measurement of the bathing medium was taken. The ratio of the first and second absorbance measurements was defined as the relative leakage ratio (RLR).
119
the cherries in the open bin decreased from 95 to about 75% while in the orchard and dropped to 35% during transport to the packing house (Fig. 1b). Relative humidity within the covered bins was at 100% for most of the time until they were received at the packing house. Fruit that had been handled in the reflective tarp-covered bins retained the best stem quality through the 4 weeks of storage, retaining a color score of greater than 3 (Table 1). Stems of fruit from the uncovered bins rated below 2 (\ 50% brown), which would be considered unacceptable. Stem quality was largely determined within the first 2 days after harvest (week 0), with little or no change occurring after that time. This indicates that damage was incurred during handling in the field and/or during transport. Water retention in the stems was also significantly (P5 0.001) better for cherries that had been handled in reflective tarp-covered bins
2.4. Statistical analyses Data presented are means of two 25 fruit subsamples from each of the three replicates that were evaluated at 0, 2 and 4 weeks. The data were analysed using the General Linear Models (GLM) procedure of SAS (SAS, Cary, NC).
3. Results In the orchard and enroute to the packing house, the temperature of the ‘Lapins’ fruit pulp in uncovered bins increased gradually from 20 °C to a maximum of 25.2 °C (Fig. 1a). The fruit pulp temperature of cherries in the reflective tarp covered bins remained relatively constant at approximately 23 °C in the orchard and enroute to the packing house. The RH in the airspace between
Fig. 1. Cherry fruit pulp temperature (a) and relative humidity within the airspace between the fruits (b) recorded for ‘Lapins’ cherries during harvest and transport to the packing house.
J.L. Schick, P.M.A. Toi6onen / Posthar6est Biology and Technology 25 (2002) 117–121
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Table 1 The effects of reflective tarps on pitting, decay, stem color, stem water content and stem tissue relative leakage ration (RLR) in ‘Lapins’ cherries Treatment
Storage duration Pitting (% fruit Decay (% fruit (weeks) affected) affected)
Stem color (1–4 scale)a
Stem water content (% fresh weight)
RLRb
Open
0 2 4
48.7 81.3 92
0 2 7.3
2.1 1.7 1.7
54.5 55 49.9
– 0.54 0.64
Tarp
0 2 4
38 60.0 76.7
0 0 4.7
3.1 3.4 3
63.3 62.6 57.8
– 0.28 0.44
** ** NS 14.6
NS ** NS 5.3
** NS NS 0.6
** ** NS 2.2
** ** NS 0.16
Significancec Treatment (T) Time (W) T×W LSDPB0.05 a
4= 0–25% of the stem surface being brown, 3 = 25–50% of the surface being brown, 2 =50–75% of the surface being brown and 1= 75–100% of the surface being brown. b RLR, relative leakage ratio. c ** Significant at the PB0.01 level; NS, not significant. The values represent the means of two subsamples comprised of 25 fruit, replicated three times.
(Table 1). Stem water loss occurred during storage in all treatments, but stems of fruit from covered bins had approximately 10% greater water content compared with stems of fruit from uncovered bins. In addition, the membrane integrity of stem tissue was greatest in cherry stems for fruit handled in reflective tarp-covered bins as indicated by a lower RLR value throughout the storage period (Table 1). At week 2, RLR of the stem tissue for cherries handled in uncovered bins was almost double compared with those that had been protected by the reflective tarps. Fruit quality retention was also improved with the use of the reflective tarps at harvest and during transport. Surface pitting incidence was lower for fruit handled in the reflective tarp-covered bins (Table 1). Incidence of decay was slightly lower for fruit which had been handled in reflective tarp-covered bins, however, this was not statistically significant.
4. Discussion The relationship between temperature, humidity and fruit moisture loss is due to the water vapor pressure deficit (WVPD) between the tissues and the surrounding air and the ability of the tissue to resist this driving force (Patterson, 1987). WVPD increases with increasing temperature and decreasing humidity. Compared with other produce, sweet cherries have low skin diffusion resistance (Patterson, 1987; Crisosto, 1992). Micke and Mitchell (1968) reported 1.5% total cherry fruit weight loss during open truck transit of less than 1 h. Cherry stems lose water about 14 times faster than the fruit (Seske, 1996), therefore it is imperative that they be protected even if they are in transit for only a short time. In this study, the tarps prevented dehydration of the stems as indicated by the significantly higher water contents for fruit handled in reflective tarp-covered bins. Dessication
J.L. Schick, P.M.A. Toi6onen / Posthar6est Biology and Technology 25 (2002) 117–121
stress leads to loss of membrane integrity (Levitt, 1972). Loss of membrane integrity leads to loss of cellular compartmentation which consequently allows polyphenol oxidase (PPO) and polyphenol substrates to mix in the damaged cells, resulting in tissue browning (Vamos-Vigyazo, 1981). Stems of cherries exposed to direct sun during harvest and transportation had higher relative leakage ratios and subsequently developed higher levels of stem browning. The rate of surface pit formation in cherries increases under higher temperatures and low levels of humidity (Patterson, 1987). In this experiment, significantly fewer fruit developed pitting when protected by reflective tarps at harvest and during transport. Exposure to the sun also contributes to increased decay (Patterson, 1987; Hansen, 1999). Low levels of decay were observed in ‘Lapins’ cherries and while reflective tarp-covered fruit had less decay, the effect was not significant. However, reflective tarps did reduce decay in ‘Lambert’ cherries in another study where a high incidence occurred from fruit in that particular orchard (data not shown).
5. Conclusion Cherries are harvested and transported to local markets during the hottest time of the year in the Pacific Northwest. Precautions need to be taken to keep cherries cool and prevent dessication of the fruit. Reflective tarps were effective in maintaining cherry quality when used immediately after harvest in the orchard, and during transit to packing house.
Acknowledgements We would like to thank Jake van Weston for allowing access to his orchard and crop during commercial harvest. We thank Sabina Stan for her technical assistance. This project was supported by the Sun Fresh Co-operative and the
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Agriculture and Agri-food Canada Matching Investment Initiative. References Crisosto, C.H., 1992. Sweet cherry harvest, postharvest handling and storage. WSU Tree Fruit Postharvest J. 3, 3 – 6. Dewey, D.H., 1951. The effects of air blast precooling on the moisture content of stems of cherries and grapes. Amer. Soc. for Hort. Sci. Tech. Paper No. 333, Dept. of Veg. Crops, Cornell Univ., Ithaca, NY, 6 pp. DeYoe, D., Holbo, H.R., Waddell, K., 1985. Seedling protection from heat stress between lifting and planting. Forest Res. Lab., Tech. Paper No. 1979, Oregon State Univ, Corvallis, OR, 2 pp. Drake, S.R, Kupferman, E.M., Fellman, J.K., 1988. ‘Bing’ sweet cherry (Prunus a6ium L.) quality as influenced by wax coatings and storage temperature. J. Food Sci. 53, 124 – 126. Haas, M. 1996. Marketing Report. B.C. Fruit Packers Cooperative Newsletter-July/August. Hansen, M., 1999. Temperature is key to postharvest handling. Good Fruit Grower 50 (8), 36. Hevia, F., Wilkens, R., Lanuza, P., Mujica, C., Olave, Y., 1998. Influence of hydrocooling and fruit color on the behavior of bing sweet cherries after refrigerated storage. Acta Hort. 468, 731 – 736. Levitt, J., 1972. Responses of Plants to Environmental Stresses. Academic Press, New York, p. 697. Micke, W.C., Mitchell, F.G., 1968. Handling cherries to maintain top quality and shelf life. Wash. State Hort. Assoc. Proc. 64, 213 – 218. Patterson, M.E, 1987. Factors of loss and the role of heat removal for maximum preservation of sweet cherries. WSU Postharvest Pomology Newsletter 5 (1), 3 – 9. Redman, R.E., Heraldson, J., Gusta, L.V., 1986. Leakage of UV-absorbing substances as a measure of salt injury in leaf tissue of woody species. Physiol. Plant. 67, 87 – 91. Seske, L., 1996. Respiration and storage potential in Norwegian-grown sweet cherries. Acta Hort. 410, 357 – 362. Siegelman, H.W., 1952. Brown discoloration and shrivel of cherry stems. J. Am. Soc. Hort. Sci. 61, 265 – 269. Thompson, J.F., Grant, J., Kupferman, E.M, Knutson, J., 1997. Reducing sweet cherry damage in postharvest operations. HortTechnology 7, 134 – 138. Vamos-Vigyazo, L., 1981. Polyphenol oxidase and peroxidase in fruits and vegetables. CRC Crit. Rev. Food Sci. Nutr. 15, 49 – 127. Young, C., Kupferman, E.M., 1994. In-field hydro cooling —cherry temperature management. WSU Tree Fruit Postharvest J. 5, 20 – 21.
Short communication
Reflective tarps at harvest reduce stem browning and improve fruit quality of cherries during subsequent storage Joanne L. Schick, Peter M.A. Toivonen * Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland Research Centre, Summerland, BC, Canada V 0H 1Z0 Received 7 November 2000; accepted 23 June 2001
Abstract The use of a reflective tarp, previously used in forestry, was assessed for its potential to improve the quality retention of sweet cherries (Prunus a6ium L.). The tarp was applied as a cover to bins of harvested cherries in the orchard and also during open-truck transport to the packing house. Controls were bins left uncovered in the orchard and during transport. Harvesting took place in 8-year-old orchards of ‘Lapins’ cherries where the foliar canopy provided very little shade. The results show that the use of reflective tarps can improve the retention of sweet cherry quality when subsequently stored in MAP bags for several weeks. Crown Copyright © 2002 Published by Elsevier Science B.V. All rights reserved. Keywords: Prunus a6ium L.; Postharvest handling; Temperature; Humidity; Modified atmosphere packaging; Reflective (laminated Mylar) film
1. Introduction Stem browning continues to be a problem for sweet cherry marketing in British Columbia, Canada and Washington State, USA (Haas, 1996; Thompson et al., 1997). Temperature and humidity are two factors that have been implicated in stem browning of sweet cherries (Dewey, 1951; Siegelman, 1952). After harvest, both heat from the sun and heat of respiration from the cherry fruit contribute to heat loading of the cherries (Young and Kupferman, 1994). Maintaining
Centre Contribution Number 2100. * Corresponding author. Tel.: +1-250-494-6386; fax: + 1250-494-0755. E-mail address: [email protected] (P.M.A. Toivonen).
lower fruit temperatures immediately after harvest results in firmer fruit with reduced decay and greener stems (Drake et al., 1988; Young and Kupferman, 1994). The optimum relative humidity for storage of sweet cherries has been reported to be between 90 and 95% (Hevia et al., 1998). Relative humidity in this range is particularly important in maintaining green stem color. Water evaporates much more quickly from cherry stems than from the fruit (Seske, 1996) and dessication is generally related to stem browning (Drake et al., 1988). It is clear that deterioration in fruit and stem quality can occur rapidly and therefore improved strategies to moderate both temperature and humidity immediately after harvest should be developed.
0925-5214/02/$ - see front matter. Crown Copyright © 2002 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 5 2 1 4 ( 0 1 ) 0 0 1 4 5 - 4
118
J.L. Schick, P.M.A. Toi6onen / Posthar6est Biology and Technology 25 (2002) 117–121
Reflective materials have been used during reforestation to protect seedlings from heat stress (DeYoe et al., 1985). These tarps are constructed of a Mylar® material sandwiched between a white painted surface and a shiny silver metallic surface. The reflective tarps have been shown to maintain temperature of seedlings equivalent to that of deep shade. They are easy to use and provide a useful tool for forest tree replanting projects in remote areas where refrigeration is unavailable. It was hypothesized that this reflective material could have beneficial effects when used to protect commercially harvested fresh fruit crops. The objectives of this work were: (1) to determine if the use of reflective tarps during harvest and transport could reduce cherry fruit temperature and maintain relative humidity around the fruit; and (2) to determine if the use of reflective tarps is beneficial to subsequent cherry quality during storage in plastic film packages.
2. Materials and methods
2.1. Experimental Reflective tarps (Silvicool III, lightweight) were supplied by Bushpro Supplies (668 Irish Creek Road, Vernon, BC). This reflective tarp is of laminated construction, consisting of a woven polyester core which is double coated with bright white on the outer surface and a silvered Mylar® on the under surface. The tarps were used with the white side facing the sun and the shiny metallic silver surface facing the fruit as this orientation has been shown to be the most effective in preventing heat stress when used on seedlings in reforestation. (DeYoe et al., 1985). Fruit temperature during harvest and transport was measured by miniature temperature/humidity data loggers (model H8, Onset computer Corporation, Pocasset, MA). An extendable temperature sensor was inserted inside the cherry fruit and the loggers were placed into the middle of the bins. The data loggers were placed so they also recorded the relative humidity in the airspace immediately surrounding the cherries. The air temperature and relative humidity within the tree
canopy in the orchard were monitored using the same type of data loggers and these were protected from direct sun exposure by a tent cover which was constructed out of plain white cardboard. This experiment was set up in a commercial orchard of 8-year-old ‘Lapins’ cherry trees on July 15, 1998 beginning at 09:00 h. The average ambient air temperature within the tree canopy during the test was 24.99 0.5 °C, while the average ambient humidity was 339 1%. Three pairs of bins were selected randomly in the orchard during a commercial harvest. Pickers filled a bin within approximately 20 min. One bin of each pair was covered with a reflective tarp and one bin was left as an uncovered control. After filling, the bins remained in the orchard between the tree rows for 4 h, as per practice in that orchard. The bins were then transported on an open flatbed trailer to the packing house in Naramata, British Columbia. The cherries were room-cooled overnight and the following morning they were delivered by a refrigerated truck to the cherry packing facility. Cherry samples were randomly selected from the top, middle and bottom layer of each of the experimental bins and packaged in 1 kg styrene ‘clamshell’ trays. All samples were transported by refrigerated truck to Pacific Agri-Food Research Centre at Summerland, British Columbia. The filled ‘clamshell’ trays were sealed in bags of a polyolefin film (PD-941, Cryovac, Duncan, SC) and stored at 1 °C, 75% RH. This film does not allow significant atmospheric modification, but does maintain a high humidity around the fruit. The atmospheres measured in the bags averaged at 0.7% CO2 and 19.42% O2 during storage. The quality of the cherries was evaluated the next day (i.e. week 0) on one set of samples and subsequently at week 2 and 4 of storage on other sets of samples.
2.2. Quality e6aluations Twenty-five randomly selected fruit from each tray were scored for pitting and decay. Fruit decay was assessed as a percent of fruit from a 25 fruit sample showing any type of decay, however,
J.L. Schick, P.M.A. Toi6onen / Posthar6est Biology and Technology 25 (2002) 117–121
the decay organisms were not identified. Pitting was evaluated and recorded as a percentage of 25 fruit showing visible pitting. The stems of the fruit were rated for color using a four point index: 4=0 – 25% of the stem surface being brown, 3 = 25 – 50% of the surface being brown, 2 =50 –75% of the surface being brown and 1 =75 –100% of the surface being brown. The stems were then weighed and dried at 60 °C in a vacuum oven for 24 h and then reweighed. The percentage water content of the stems were calculated using the initial (fresh) and final (dry) weights.
2.3. UV-absorbing solute leakage measurements Tissue leakage of the stems was determined using the method described by Redman et al. (1986). Ten stems were cut with a razor blade into sections of 1 mm length and leakage determined over a two hour incubation at room temperature by measuring absorbance of the bathing medium at 280 nm. The samples were then frozen at − 20 °C, thawed and a second absorbance measurement of the bathing medium was taken. The ratio of the first and second absorbance measurements was defined as the relative leakage ratio (RLR).
119
the cherries in the open bin decreased from 95 to about 75% while in the orchard and dropped to 35% during transport to the packing house (Fig. 1b). Relative humidity within the covered bins was at 100% for most of the time until they were received at the packing house. Fruit that had been handled in the reflective tarp-covered bins retained the best stem quality through the 4 weeks of storage, retaining a color score of greater than 3 (Table 1). Stems of fruit from the uncovered bins rated below 2 (\ 50% brown), which would be considered unacceptable. Stem quality was largely determined within the first 2 days after harvest (week 0), with little or no change occurring after that time. This indicates that damage was incurred during handling in the field and/or during transport. Water retention in the stems was also significantly (P5 0.001) better for cherries that had been handled in reflective tarp-covered bins
2.4. Statistical analyses Data presented are means of two 25 fruit subsamples from each of the three replicates that were evaluated at 0, 2 and 4 weeks. The data were analysed using the General Linear Models (GLM) procedure of SAS (SAS, Cary, NC).
3. Results In the orchard and enroute to the packing house, the temperature of the ‘Lapins’ fruit pulp in uncovered bins increased gradually from 20 °C to a maximum of 25.2 °C (Fig. 1a). The fruit pulp temperature of cherries in the reflective tarp covered bins remained relatively constant at approximately 23 °C in the orchard and enroute to the packing house. The RH in the airspace between
Fig. 1. Cherry fruit pulp temperature (a) and relative humidity within the airspace between the fruits (b) recorded for ‘Lapins’ cherries during harvest and transport to the packing house.
J.L. Schick, P.M.A. Toi6onen / Posthar6est Biology and Technology 25 (2002) 117–121
120
Table 1 The effects of reflective tarps on pitting, decay, stem color, stem water content and stem tissue relative leakage ration (RLR) in ‘Lapins’ cherries Treatment
Storage duration Pitting (% fruit Decay (% fruit (weeks) affected) affected)
Stem color (1–4 scale)a
Stem water content (% fresh weight)
RLRb
Open
0 2 4
48.7 81.3 92
0 2 7.3
2.1 1.7 1.7
54.5 55 49.9
– 0.54 0.64
Tarp
0 2 4
38 60.0 76.7
0 0 4.7
3.1 3.4 3
63.3 62.6 57.8
– 0.28 0.44
** ** NS 14.6
NS ** NS 5.3
** NS NS 0.6
** ** NS 2.2
** ** NS 0.16
Significancec Treatment (T) Time (W) T×W LSDPB0.05 a
4= 0–25% of the stem surface being brown, 3 = 25–50% of the surface being brown, 2 =50–75% of the surface being brown and 1= 75–100% of the surface being brown. b RLR, relative leakage ratio. c ** Significant at the PB0.01 level; NS, not significant. The values represent the means of two subsamples comprised of 25 fruit, replicated three times.
(Table 1). Stem water loss occurred during storage in all treatments, but stems of fruit from covered bins had approximately 10% greater water content compared with stems of fruit from uncovered bins. In addition, the membrane integrity of stem tissue was greatest in cherry stems for fruit handled in reflective tarp-covered bins as indicated by a lower RLR value throughout the storage period (Table 1). At week 2, RLR of the stem tissue for cherries handled in uncovered bins was almost double compared with those that had been protected by the reflective tarps. Fruit quality retention was also improved with the use of the reflective tarps at harvest and during transport. Surface pitting incidence was lower for fruit handled in the reflective tarp-covered bins (Table 1). Incidence of decay was slightly lower for fruit which had been handled in reflective tarp-covered bins, however, this was not statistically significant.
4. Discussion The relationship between temperature, humidity and fruit moisture loss is due to the water vapor pressure deficit (WVPD) between the tissues and the surrounding air and the ability of the tissue to resist this driving force (Patterson, 1987). WVPD increases with increasing temperature and decreasing humidity. Compared with other produce, sweet cherries have low skin diffusion resistance (Patterson, 1987; Crisosto, 1992). Micke and Mitchell (1968) reported 1.5% total cherry fruit weight loss during open truck transit of less than 1 h. Cherry stems lose water about 14 times faster than the fruit (Seske, 1996), therefore it is imperative that they be protected even if they are in transit for only a short time. In this study, the tarps prevented dehydration of the stems as indicated by the significantly higher water contents for fruit handled in reflective tarp-covered bins. Dessication
J.L. Schick, P.M.A. Toi6onen / Posthar6est Biology and Technology 25 (2002) 117–121
stress leads to loss of membrane integrity (Levitt, 1972). Loss of membrane integrity leads to loss of cellular compartmentation which consequently allows polyphenol oxidase (PPO) and polyphenol substrates to mix in the damaged cells, resulting in tissue browning (Vamos-Vigyazo, 1981). Stems of cherries exposed to direct sun during harvest and transportation had higher relative leakage ratios and subsequently developed higher levels of stem browning. The rate of surface pit formation in cherries increases under higher temperatures and low levels of humidity (Patterson, 1987). In this experiment, significantly fewer fruit developed pitting when protected by reflective tarps at harvest and during transport. Exposure to the sun also contributes to increased decay (Patterson, 1987; Hansen, 1999). Low levels of decay were observed in ‘Lapins’ cherries and while reflective tarp-covered fruit had less decay, the effect was not significant. However, reflective tarps did reduce decay in ‘Lambert’ cherries in another study where a high incidence occurred from fruit in that particular orchard (data not shown).
5. Conclusion Cherries are harvested and transported to local markets during the hottest time of the year in the Pacific Northwest. Precautions need to be taken to keep cherries cool and prevent dessication of the fruit. Reflective tarps were effective in maintaining cherry quality when used immediately after harvest in the orchard, and during transit to packing house.
Acknowledgements We would like to thank Jake van Weston for allowing access to his orchard and crop during commercial harvest. We thank Sabina Stan for her technical assistance. This project was supported by the Sun Fresh Co-operative and the
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