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Chien Wang*

The objective of this study was to determine if treatment with methyl jasmonate (MJ), a naturally occurring substance, would extend the shelf life of tomato slices, specifically when slices were cut from fruit previously treated with this natural product. Tomatoes were harvested at breaker stage. The fruit were divided into four lots. The first three lots were treated with MJ right after harvest at the breaker stage. Fruit from the first lot were sliced immediately after MJ treatment. Fruit from the second lot were placed at 20 °C and allowed to ripen to red stage before slicing. Fruit from the third lot were treated the same way as those in the second lot except they received an additional MJ treatment just before slicing. Fruit from the fourth lot were placed at 20 °C and allowed to ripen to red stage before MJ treatment and slicing. Each lot also included an untreated control. MJ treatments were carried out in 200-L airtight containers. MJ was spotted onto filter paper at final vapor concentration of 10-5 M. Fruit were cut with a meat slicer to obtain slices with 5-mm thickness. Slices were placed in 1-L clear plastic trays with lids and stored at 5 °C. Samples were transferred daily from 5 to 20 °C for evaluation. Fresh-cut tomatoes treated with MJ and sliced at breaker stage (lot 1) had less decay, better quality, and longer shelf life than the untreated slices. However, no differences were found between the control slices and treated slices at the red stage regardless the time of MJ treatment and whether or not additional MJ treatments were applied (lots 2, 3 & 4). The results indicate that the effectiveness of MJ in reducing decay and maintaining quality is affected by the stages of ripeness of tomatoes and the types of decay.

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Chien Wang

Berry fruits such as blackberries (Rubus sp.) and blueberries (Vaccinium corymbosum L.) are highly perishable after harvest. In addition to rapid deterioration in quality, they are also very susceptible to microbial invasion. The shelf life of these berries is usually terminated by decay. Several natural antimicrobial compounds derived from essential oils of plants were studied for their efficacies in inhibiting decay and extending shelf life of berry fruits. The severity of decay in blackberries and blueberries stored at 10 °C was significantly reduced by treatment with thymol. Treatments with menthol or eugenol also suppressed the fungal growth, but to a lesser extent. All of these three natural antimicrobial compounds extended shelf life of blackberries and blueberries as compared to the control. Berries treated with thymol, menthol, or eugenol also maintained better fruit quality with higher levels of sugars, organic acids, and oxygen radical absorbance capacity than the untreated fruits. The effects of these natural antimicrobial agents on the quality and shelf life of other fruits will be investigated.

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Chien Yi Wang

The activities of catalase and superoxide dismutase decreased while peroxidase activity increased in zucchini squash (Cucurbita pepo L., cv. `Elite') during storage at 5°C. Preconditioning of squash at 15°C for 2 days prior to the cold storage reduced the decline of catalase activity and suppressed the increase in peroxidase activity. The superoxide dismutase activity remained higher in temperature conditioned squash than in untreated squash. These results indicate that acclimation to chilling temperature in squash may also involve modifications in the activities of catalase, peroxidase, and superoxide dismutase.

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Chien Yi Wang

Temperature conditioning of zucchini squash (Cucurbita pepo L.) at 15°C for 2 days enhanced polyamine levels and delayed the development of chilling injury during storage at 5°C. Direct treatment of zucchini squash with polyamines increased the endogenous levels of polyamines and reduced chilling injury. However, treatment with polyamine inhibitors after harvest but before temperature conditioning suppressed the increase of endogenous polyamines and reduced the benefit obtained from temperature conditioning. These results suggest that the resistance of squash to chilling injury may be related to the endogenous levels of polyamines.

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Chien Yi Wang

Chilling injury inhibits the growth and development of tropical plants and shortens the postharvest life of tropical horticultural commodities. This presentation will emphasize the postharvest aspects of chilling injury. While most tropical commodities are sensitive to temperatures below 10 to 15C, specific critical temperatures may vary with the species, stage of development, and type of tissue. Likewise, symptoms of chilling injury also vary with different commodities. Reduction of chilling injury can be achieved either by increasing the tolerance to chilling in sensitive tissues or by delaying the development of chilling injury symptoms. Some methods involve the manipulation and modification of the storage environment, whereas other techniques involve direct treatment to the commodities. Specific examples of the alleviation of chilling injury in various tropical commodities will be discussed.

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Chien Yi Wang

The endogenous levels of abscisic acid (ABA) in zucchini squash were increased by temperature conditioning at 10°C for 2 days. This temperature conditioning treatment reduced the severity of chilling injury in the squash during subsequent storage at 2.5°C. The ABA levels remained higher in treated squash than in untreated samples throughout storage. Direct treatments of squash with ABA at 0.5 mM and 1 mM before storage at 2.5°C increased ABA levels in the tissue and were also effective in reducing chilling injury. The involvement of ABA in reducing chilling injury will be discussed.

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Chien Yi Wang

Cucumbers (Cucumis sativus L.) and zucchini squash (Cucurbita pepo L.) were pressure-infiltrated (82.7 kPa for 3 min) with methyl jasmonate (MJ) in aqueous suspension and then stored at a chilling temperature of 5C. Control fruit were infiltrated with distilled water and handled in a similar manner. Treatment with MJ delayed the onset and reduced the severity of chilling injury symptoms in both cucumbers and zucchini squash. Analysis of polyamines in zucchini squash showed that putrescine increased with time in storage at 5C, while spermidine and spermine decreased during the same period. MJ treatment did not have an appreciable effect on putrescine, but the treated fruit maintained higher levels of spermidine and spermine than the control fruit throughout storage at 5C.

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Chien Y. Wang

Mature leaves of kale (Brassica oleracea L., Alboglabra group) and collard (Brassica oleracea L., Acephala group), and Brussels sprouts (Brassica oleracea L., Gemmifera group) were heated by moist air at 40, 45, 50, or 55 °C for durations of 0, 30, 60, or 90 minutes. Heating of kale at 45 °C for 30 minutes was effective in maintaining better postharvest quality, delaying yellowing, and reducing losses of sugars and organic acids during subsequent storage at 15 °C. Exposure of collard at 40 °C for 60 minutes also delayed yellowing and maintained turgidity of the leaves. Other treatments were either less beneficial, not effective, or caused injury. Heat injury occurred when temperature and duration exceeded the tolerance levels. In some cases, heat-injured tissues remained green but developed fungal infection. Heat treatments had no measurable effects on the rate of senescence or storage quality of Brussels sprouts.