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Susan Lurie and Joshua D. Klein

Apples (Malus domestica Borkh. cv. Anna) were treated at harvest by a dip in 3% CaCI2 solution, heated for 4 days at 38C, or the two treatments combined, before being placed in OC storage. After removal of the apples from storage and holding them for 1 week at 20C, the combined treatment maintained fruit quality best. The fruit remained firmer than with either treatment separately, and peel yellowing and decreased titratable acidity caused by the heat treatment were less pronounced. Heat treatment alone maintained fruit firmness, while CaCI2 alone had no effect on fruit quality, although it raised the fruit calcium level more than the combined treatment in most experiments. Altering the temperature (0, 20, or 38C) of the CaCl2 dip did not change its efficacy. There was less soluble and more insoluble pectin in cell wall extracts of apples from the combined treatment than from other treatments. In addition, proportionally less Ca was present in the water-soluble pectin fraction of the combined treatment compared to other treatments, indicating different binding properties in the cell wall.

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Joshua D. Klein and Susan Lurie

`Anna' and `Granny Smith' apples (Malus domestics Borkh.) that were kept at 46C for 12 hours or at 42C for 24 hours before storage at 0C were firmer at the end of storage and had a higher soluble solids: acid ratio and a lower incidence of superficial scald than unheated fruit. These heat regimes produced results similar to those obtained by keeping fruit at 38C for 72 or 96 hours before storage. Prestorage regimes of 46C for 24 hours or 42C for 48 hours resulted in fruit damage after storage.

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Joshua D. Klein and Susan Lurie

Commercial, ecological, and agrotechnical considerations have recently renewed interest in the use of physical rather than chemical means to maintain postharvest quality of horticultural crops. This review discusses prestorage heat treatments that protect against physiological disorders, enhance natural resistance to pathogen infection, reversibly inhibit fruit ripening, and permit flexibility in storage temperatures.

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Joshua D. Klein and Susan Lurie

The benefits conferred by a prestorage heat treatment on poststorage quality of apples (Malus domestics Borkh.) were measured on `Anna', a non-storing early cultivar, and `Granny Smith', a long-storing late cultivar. The major benefit was a decrease in rate of apple softening, both during OC storage and during simulated shelf life at 20C. Soluble solids concentration was not affected by heat treatment, but titratable acidity was reduced. Ethylene production after heat treatment and storage was similar to or higher than that of control apples, but respiration was lower. The optimum temperature and time combination for prestorage treatment of both cultivars was 4 days at 38C.

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Susan Lurie and Joshua D. Klein

Mature-green tomato (Lycopersicon esculentum Mill.) fruit, when kept for 3 days at 36, 38, or 40C before being kept at 2C for 3 weeks, did not develop chilling injury, while unheated fruit placed at 2C immediately after harvest did. When removed from 2 to 20C, the heated tomatoes had lower levels of K+ leakage and a higher phospholipid content than unheated fruit. Sterol levels were similar in heated and unheated fruit while malonaldehyde concentration was higher in heated fruit at transfer to 20C. The unheated tomatoes remained green, and brown areas developed under the peel; their rate of CO2 evolution was high and decreased sharply, while ethylene evolution was low and increased at 20C. In contrast, the heat-treated tomatoes ripened normally although more slowly than freshly harvested tomatoes: color developed normally, chlorophyll disappeared, and lycopene content increased, CO2, and ethylene evolution increased to a climacteric peak and K+ leakage increased with time. During prestorage heating, heat-stress ethylene production was inhibited, protein synthesis was depressed, and heat-shock proteins accumulated. There appears to be a relationship between the “heat shock response” and the protection of tomato fruit from low-temperature injury.

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Joshua D. Klein and Susan Lurie

Apple (Malus domestica Borkh. `Grand Alexander') fruit were stored immediately at 0C after harvest or after being held at 38,42, or 46C for 72,24, or 12 h, respectively. Half of each fruit lot was dipped in 1.5 % CaCl before storage. Heating did not appreciably affect Ca uptake into epidermal or cortical tissue. Calcium and heat treatments acted synergistically in reducing the severity of superficial scald and in retaining fruit firmness after 5 months of storage, relative to nontreated or nonheated Ca-dipped fruit.

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Saichol Ketsa, Sugunya Chidtragool and Susan Lurie

Freshly harvested mango fruit (Mangifera indica L. cv. Nam Dok Mai), were heated at 38 °C for 3 days or heated and then stored at 4 °C for 3 weeks before ripening at 25 °C, then compared with nonheated fruit for quality changes. When not refrigerated, heated and nonheated fruit ripened within 7 days to a comparable quality, although titratable acidity remained higher in heated fruit. The peel of heated fruit was initially yellower in cold-stored fruits, and soluble solids content was initially greater, whereas firmness and titratable acidity were less than that of nonheated fruit during ripening at 25 °C. After cold storage and ripening, heated fruit had a lower incidence of disease and developed less chilling injury than nonheated fruit. Nonheated fruit stored at 4 °C also developed off-flavors whereas the heated fruit did not. Heat treatment did not inhibit ripening but did ameliorate low-temperature injury.

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Susan Lurie, Reuven Ronen and Beny Aloni

Bell pepper (Capsicum annuum L.) plants were sprayed at full bloom with paclobutrazol (50 and 100 mg·liter–1), uniconazole (20 and 50 mg·liter–1), or mefluidide (20 and 50 mg·liter–1). Mature-green and red fruit were harvested 4 and 8 weeks after spraying, respectively. Paclobutrazol and uniconazole, but not mefluidide, affected plant growth and fruit morphology. All three growth regulators alleviated chilling injury that developed on green and red peppers after 28 days at 2C. Potassium leakage was lower from tissue disks, and weight loss less, from treated fruit than from control fruit. Ethylene and CO2 production at 20C were similar in control and paclobutrazol-treated fruit after 28 days at 2C. These results are consistent with previous findings that showed these growth regulators are able to increase tolerance to low temperatures in whole plants. Chemical names used: N-[2,4-dimethyl-5-trifluoromethyl sulfonyl amino phenyl acetamide] (mefluidide); (2RS, 3RS) 1-(4-chlorophenyl)-4,4 dimethyl-2-(1,2,4-triazol-1-yl)-pentan-3-ol (paclobutrazol); (E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4 triazol-1-yl)-pentan-3-ol (uniconazole).

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Zohar Shaham, Amnon Lers and Susan Lurie

`Granny Smith' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] were harvested in two seasons and stored at 0 °C air storage with no pretreatment (control), after heating for 4 d at 38 °C, or after treating for 16 hours at 20 °C with 1 μL·L-1 1-methylcyclopropene (1-MCP). The effects of the two treatments on superficial scald development were consistent over both seasons. Scald began to appear after 8 weeks in control fruit, after 16 weeks in heated fruit but not on 1-MCP treated fruit. α-Farnesene accumulation and oxidation were slower in the skin of heated than in control fruit, and almost entirely absent in 1-MCP treated fruit. The activities of five antioxidant enzymes, ascorbate peroxidase, catalase, glutathione reductase, peroxidase and superoxide dismutate, were measured at two-week intervals in the apple peel, quantitatively as total activity and qualitatively by isozyme analysis. Enzyme activities either increased or remained stable during 16 weeks of storage, except for superoxide dismutase activity, which decreased. Ascorbate oxidase activity was higher in heated than control apples and there was an additional peroxidase isozyme present in activity gels. The activities of antioxidant enzymes were lower in 1-MCP treated fruit except for catalase during the first month of storage. Lipid soluble antioxidant activity was higher in 1-MCP treated fruit than the fruit of the other treatments, and water soluble antioxidant activity was higher in both treatments than in control fruit during the time that scald was developing in control apples. Both free and total phenol contents in the peel fluctuated during storage but no consistent trend was detected. The differences in enzyme activity and antioxidant content of the peel of 1-MCP and heated apples may play a role in preventing or delaying the appearance of superficial scald.

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Susan Lurie, Reuven Ronen and Shimon Meier

Storing `Maor' green bell peppers (Capsicum annuum L.) for 3 weeks at 2C resulted in the development of chilling injury (CI) evidenced as surface pitting. Fruit held at 8C did not develop any CI symptoms, but, after 3 weeks of storage, the fruit began to change color from green to red. PAM fluorometry was used to measure changes in photosynthetic competency in whole green bell peppers. Three photosynthetic characteristics could be measured by this method: quantum yield (Fm/Fe), photochemical quenching (Qp), and nonphotochemical quenching (Qnp). Fm/Fo decreased 90% during the first week of storage at 2C and remained low thereafter, while Qnp decreased after 2 weeks at 2C, just before the peppers began to develop CL Qp was similar at both storage temperatures. Potassium leakage as a CI measurement also increased in excised pepper discs after 2 weeks at 2C. The results indicate that PAM fluorometry can measure CI nondestructively before tissue damage is visible in green peppers.