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  • Author or Editor: Myrna Nisperos-Carriedo x
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Application of edible coatings that can simulate controlled atmosphere storage has become a popular concept. An experimental coating developed at the USDA Winter Haven laboratory, Nature-Seal (patent application #07/679,849), or a commercial composite coating was applied to papaya fruit at the green (immature) stage for comparison to uncoated fruit. Both types of coatings contain a polysaccharide base and therefore have different properties than most commercial “wax” coatings. The fruit were stored continuously at 21C or 3 days at 13C then ripened at 21C with 95 to 98% RH. Sample fruit from each treatment were analyzed for color, weight loss, CO2 ethylene, & % decay and softening. Results showed substantial extension of papaya shelf-life when the fruit were coated with Nature Seal while the commercial coating was less effective. This effect was due to retardation of ripening as evidenced by delayed color development, softening, and effect of coating permeability to CO2 and O2 on climacteric CO2 and ethylene production.

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Edible lipid and composite films were tested for their ability to retain flavor volatiles in `Pineapple' orange fruits stored at 21° using a headspace analysis technique. Volatiles, considered to be important to fresh orange flavor, were quantified and acetaldehyde, ethyl acetate, ethyl butyrate and methyl butyrate increased progressively during storage in coated fruits. Acetaldehyde increased by the second day of storage in uncoated fruits but declined thereafter, `Sunny' tomato fruits were harvested at the green or breaker stage of maturity and ripened at 32.5, 21.0 and 12.9°C. Some fruit from the higher and lower storage temperatures were moved to 21° after one week. In most cases major or important flavor volatiles were highest in fruit transferred to or continuously stored at 21.0°C followed by 12.9 and 32.5°C. Fruit harvested at the breaker stage generally had higher volatile levels compared to those harvested green.

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Edible lipid and composite films were tested for their ability to retain flavor volatiles in `Pineapple' orange fruits stored at 21° using a headspace analysis technique. Volatiles, considered to be important to fresh orange flavor, were quantified and acetaldehyde, ethyl acetate, ethyl butyrate and methyl butyrate increased progressively during storage in coated fruits. Acetaldehyde increased by the second day of storage in uncoated fruits but declined thereafter, `Sunny' tomato fruits were harvested at the green or breaker stage of maturity and ripened at 32.5, 21.0 and 12.9°C. Some fruit from the higher and lower storage temperatures were moved to 21° after one week. In most cases major or important flavor volatiles were highest in fruit transferred to or continuously stored at 21.0°C followed by 12.9 and 32.5°C. Fruit harvested at the breaker stage generally had higher volatile levels compared to those harvested green.

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Several processes including controlled atmosphere, hypobaric storage and the application of protective films have been developed to extend shelf-life of fruits and vegetables. Recently, the application of edible coatings that can simulate controlled atmosphere storage to prolong product freshness is becoming a popular concept. The ability of these coatings to extend postharvest storage life depends on their differential permeability to CO2, O2 and water vapor.

This talk will describe the developmental aspect and specific applications of edible coatings on various fresh and minimally processed fruits and vegetables.

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Minimal processing is defined as handling, preparation, and distribution of agricultural commodities in a fresh state. Cutting fresh produce results in injury, cell leakage and accelerated perishability. The presence of an artificial barrier to gas and moisture diffusion ideally would reduce moisture loss, decrease levels of internal oxygen, increase internal carbon dioxide, reduce respiration rate and wound ethylene production, and delay ripening/senescence. In practice, the degree to which the above factors can be altered for a given commodity depends on species, cultivar, surface-to-volume ratio, respiration rate, etc. An edible coating, as an artificial barrier, is made from renewable resources, is biodegradable and can be used as a carrier for antioxidants, artificial colors, flavors, growth regulators, enzyme inhibitors and preservatives. The cutting of produce, however, results in a high moisture surface which presents special problems for coating adherence and microbial control. Recent research on coating of cut mushrooms, celery, apples, pears and peeled carrots, to maintain texture and reduce discoloration, with edible composite coatings will be discussed.

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Whole tomato fruit (Lycopersicon esculentum Mill.), cvs. Sunny and Solarset, were analyzed at 5 different ripening stages for ethylene and CO2 production. Homogenates from the same fruit were prepared for determination of color, flavor volatiles, sugars and organic acids. Of the flavor volatiles measured, only eugenol decreased during ripening in both varieties and 1-penten-3-one in `Sunny' tomatoes. Ethanol, and trans-2-trans-4-decadienal levels showed no change or fluctuated as the fruit matured while all other volatiles measured (cis-3-hexenol, 2-methyl-3-butanol, vinyl guiacol, acetaldehyde, cis-3-hexenal, trans-2-hexenal, hexanal, acetone, 6-methyl-5-hepten-2-one, geranylacetone and 2-isobutylthiazole) increased in concentration, peaking in the later stages of maturity. Synthesis of some volatile compounds occurred simultaneously with that of climacteric ethylene and color. `Solarset' fruit exhibited higher levels of sugars and all flavor components except ethanol, vinyl guiacol, hexanal and 2-methyl-3-butanol in the red stage. There were no differences between these varieties for acids

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`Valencia' oranges were-treated with an experimental polysaccharide-based coating, a commercial shellac-based water wax, or were left uncoated. The fruit were stored at 16 or 21C with 95% RH. Samples were periodically analyzed for internal gases, flavor volatiles, water loss, and `Brix. Coated fruit had lower internal O2 and higher CO2 and ethylene levels as well as higher levels of many flavor volatiles (including ethanol) compared to uncoated. The differences were greatest for shellac-coated fruit at the higher storage temperature. No differences were found for °Brix. The shellac-coating gave the best weight-loss control and the most restricted gas exchange. The low gas permeability characteristic of this type of shellac coating may result in altered flavor for fruit held at 21C.

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