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Christopher B. Watkins

The inhibitor of ethylene perception, 1-methylcyclopropene (1-MCP), is the basis of a new technology that is increasingly being used to improve storage potential and maintain quality of fruit and vegetables. 1-MCP is registered for use on a number of crops, including apple, apricot, avocado, banana, broccoli, kiwifruit, pear, mango, melon, peach, nectarine, persimmon, plum, and tomato. The registered crop is often specific to country. The effects of 1-MCP on quality of these crops, as well as its effects on physiological disorders and pathological diseases, are reviewed. Most available literature on 1-MCP has focused on laboratory-based trials and little information exists about its effects on product quality at the commercial level. The apple is the most significant exception, being the first crop for which 1-MCP was used commercially and extensively around the world. The apple is a crop for which limited ripening after harvest is desirable. For many other fruit, successful commercialization of 1-MCP will require an appropriate balance between 1-MCP concentrations and exposure periods that will delay but not inhibit ripening. The effects of preharvest factors, cultivar, maturity, and postharvest practices are complex and will impact commercial success of 1-MCP-based technology. For leafy or nonfruit vegetables, the advantages of 1-MCP may only be apparent under abusive conditions such as high temperatures and exogenous ethylene exposure. Finally, commercial utilization of 1-MCP-based technology will be a function of the cost of its application relative to its benefits for each product.

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Christopher B. Watkins

The tolerances of horticultural commodities to CO2 are outlined, as are also the associated biochemical and physiological aspects of differences in tolerance between and within commodity types. These tolerances are related to responses to the use of modified atmosphere packaging (MAP) during storage. Commodities vary widely in their responses to elevated CO2, and low tolerance to the gas limits its use to maintain quality in some cases. Standard recommendations are generally those established to extend the storage period of any given commodity as long as possible, and safe atmospheres may differ substantially for shorter term exposures used in MAP. Use of MAP for storage of minimally processed products represents an important example of this, as storage periods and quality attributes required for commercial marketing of cut products can be very different from those of the whole product. Factors such as cultivar and postharvest treatment before imposing high CO2 can influence responses of commodities to CO2, but are rarely considered in cultivar selection or in commercial application. A better understanding of the physiology and biochemistry of commodity responses to CO2 is required for increased use of MAP.

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Mette Larsen and Christopher B. Watkins

Firmness and aroma composition of strawberry fruit (Fragaria ×ananassa Duch. cv. Pajaro) stored in air or treated with 20% CO2 for up to 12 days at 0C were analyzed upon removal from storage. Fruit firmness increased after 2 days in CO2, while the composition of aroma compounds in the fruit was unaffected at this time. Ethanol and ethyl hexanoate accumulated after 3 days during high CO2 treatment, but these compounds usually decreased during subsequent cold storage in air. Ethyl butanoate and ethyl acetate also accumulated but continued to increase after 6 and 9 days of CO2 storage, respectively. This study suggests that treatment of strawberry fruit with CO2 after harvest, followed by air storage at 0C, can maintain firmness while minimizing off-flavor development.

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Terence L. Robinson* and Christopher B. Watkins

In 2001 and 2002, we imposed a wide range of croploads (0-15 fruits/cm2 of TCA) on 4- and 5-year-old Honeycrisp/M.9 trees by manual hand thinning soon after bloom to define appropriate croploads that give adequate repeat bloom and also the best fruit quality. At harvest each year we evaluated fruit ripening and quality. Samples were stored for 5 months in air at 38 °F and 33 °F and evaluated for fruit firmness and storage disorders. Cropload was negatively correlated with tree growth, return bloom, fruit size, fruit red color, fruit sugar content, fruit starch content, fruit firmness, fruit acidity, fruit bitter pit, fruit senescent breakdown, fruit rot and fruit superficial scald, but was positively correlated with leaf blotch symptoms, fruit internal ethylene concentration at harvest, and fruit soggy breakdown. There was a strong effect of cropload on fruit size up to a cropload 7, beyond which there was only a small additional effect. Although there was considerable variation in return bloom, a relatively low cropload was required to obtain adequate return bloom. Fruit red color was reduced only slightly up to a cropload of 8 beyond which it was reduced dramatically. The reduced fruit color and sugar content at high croploads could indicate a delay in maturity of but, fruits from high croploads were also softer, had less starch and greater internal ethylene. It that excessive croploads advance maturity. Overall, croploads greater than 10 resulted in no bloom the next year, and poor fruit size, color and flavor, but these fruits tended to have the least storage disorders. Moderate croploads (7-8) resulted in disappointing return bloom and mediocre fruit quality. For optimum quality and annual cropping, relatively low croploads of 4-5 were necessary.

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Yosef Al Shoffe and Christopher B. Watkins

Initial short-term storage is a treatment where fruit are cooled to 33 °F for a specific time period and then moved to 38 °F until the end of storage. Its effects on the development of physiological disorders in ‘Honeycrisp’ apples (Malus domestica) were investigated for two seasons. During the first season, fruit were harvested from two orchards and stored at 33 and 38 °F, with and without 1 week of conditioning at 50 °F, or stored for 4 weeks at 33 °F followed by 4 weeks at 38 °F. All fruit were stored for a total of 8 weeks. In the second season, fruit were harvested from one orchard and stored at 38 °F either with or without 1 week of conditioning at 50 °F, or stored for 1 week at 33 °F and moved to 38 °F for 15 weeks followed by 7 d at 68 °F. Short-term storage (1 to 4 weeks) at 33 °F decreased bitter pit for all orchards in the two seasons, except in comparison with the continuous 33 °F storage in the first season; soft scald was also reduced in the first season compared with continuous storage at 33 °F, with higher incidence of soft scald in orchard one compared with orchard two. Initial short-term storage at 33 °F resulted in lower soggy breakdown incidence compared with storage at 33 °F with 1 week of conditioning at 50 °F for fruit from orchard two in the first season, the only year when low-temperature injuries were observed. In conclusion, initial short-term storage at 33 °F followed by storage at 38 °F maintained the highest percentage of healthy fruit in the two seasons.

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Jianzhi Jenny Zhang and Christopher B. Watkins

The effects of postharvest treatments of air and 20 kPa CO2 (in air) at 2 or 20 °C on color, firmness, accumulations of acetaldehyde, ethanol, and ethyl acetate, activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) activity, and expression of an ADH gene were studied in strawberry fruit (Fragaria ×ananassa Duch. cv. Jewel). CO2 treatment enhanced strawberry fruit firmness at 2 °C but not 20 °C, while the rate of color changes was affected by CO2 treatment at 20 °C but not at 2 °C. Temperature also affected the accumulation of acetaldehyde, ethanol and ethyl acetate in CO2-treated fruit. All three compounds accumulated in fruits at 2 °C. At 20 °C, ethanol accumulated slightly by day 6, although ethyl acetate accumulated in fruit from both atmospheres. PDC enzyme activity was higher in CO2-treated fruit than their air-treated control at 2 °C but not at 20 °C. ADH activity and ADH mRNA accumulation of the CO2-treated berries were higher than in air at 20 °C but not 2 °C. The results, overall, indicate that patterns of change among gene expression, enzyme activities, and fermentation product accumulation were not consistent.

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Errol W. Hewett and Christopher B. Watkins

The incidence of external and internal bitter pit in `Cox's Orange Pippin' apple (Malus domestics Borkh.) fruit sprayed with normal therapeutic sprays either with or without Ca salts at 2-week intervals during the growing season was determined after 6 weeks of storage over 7 consecutive years. Following harvest, fruit was either vacuum-infiltrated with CaCI2 or received no further treatment. Although there was a tendency for fruit that had been sprayed and vacuum-infiltrated with Ca to exhibit the greatest degree of bitter pit control, this treatment was not significantly superior to Ca sprays alone. Vacuum infiltration alone reduced the disorder to a lesser extent than Ca sprays and was more effective in reducing external than internal bitter bit. The results suggest that Ca applications over the growing season are superior to postharvest vacuum-infiltration with Ca in the prevention of bitter pit.

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William J. Bramlage and Christopher B. Watkins

Seeking non-chemical alternatives to use of DPA for scald control on apples, we interrupted storage with a brief warming period. This often reduces chilling injuries of fruit. Warming `Granny Smith apples for 5 days at 20 C after 2 weeks at 0 C reduced scald as effectively as a 1000 ppm DPA treatment at that time. To better characterize this response, we tested other timings of the warming period, and also lower warming temperature. Warming at 10 C, or for shorter times at 20 C, or after longer periods at 0 C all were less effective. Maintaining a warm period before storage was not effective. During warming of `Cortland' and `Delicious' apples softening and loss of green color occurred, the extent of which increased with warming time and usually was greater if the fruit had initiated the ethylene climacteric before warming.

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Adel A. Kader and Christopher B. Watkins

Rapid expansion of modified atmosphere packaging (MAP) for horticultural produce has occurred during the last 10 years, especially for fresh cut (minimally processed) products, but limitations to further expansion reside in both responses of products and available technology. We introduce the workshop on Modified Atmosphere Packaging—Toward 2000 and Beyond by reviewing the current status of MAP technology for fresh and minimally processed products, highlighting research needs and future advances, and providing a list of selected references on MAP published since 1989.

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Christopher B. Watkins and Jacqueline F. Nock

The effects of temperature during 1-MCP treatment, and the effects of delays of up to 8 d after harvest before treatment, have been investigated using `Cortland', `Delicious', `Jonagold', and `Empire' (normal and late harvest) apple [(Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] cultivars stored in air for 2 and 4 months and in controlled atmosphere (CA) storage for 4 and 8 months. Fruit were treated with 1 μL·L–1 1-MCP for 24 hours on the day of harvest (warm) or after 1, 2, 3, 4, 6, or 8 days at cold storage temperatures. CA storage was established by day 10. Little effect of temperature during treatment (warm fruit on the day of harvest compared with cold fruit after 24 hours of cooling) was detected. Major interactions among cultivars, handling protocols before 1-MCP treatment, storage type and length of storage were observed. Delays of up to 8 days before 1-MCP treatment either did not affect efficacy of treatment, or markedly reduced it, depending on cultivar, storage type and length of storage. The results indicate that, depending on cultivar, the importance of minimizing the treatment delay increases as storage periods increase.