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Robert A. Saftner

The ethylene precursor, 1 -aminocyclopropane- 1 -carboxylic acid (ACC), is actively transported across the tonoplast of plant cells, impacting cellular compartmentation of ACC and ethylene biosynthesis. To identify potential photoaffinity probes for identifying ACC transport-related membrane proteins, the effects of over 70 ACC and other amino acid analogs on ACC uptake into isolated maize vacuoles were investigated. Only relatively nonpolar, neutral amino acid stereoisomers of L-configuration were strong inhibitors of ACC transport. Group additions, substitutions, or deletions at the carboxyl, (x-amino and the Pro-(R) methylene, or hydrogen moieties essentially eliminated transport inhibition, whereas side-chain substitutions remained antagonistic. The kinetics of ACC and neutral L-amino acid analogs tested were competitive. The results indicate that the ACC transport system can be classified as a neutral L-amino acid carrier having a relatively high affinity for ACC and other nonpolar amino acids. The results also suggest that the carrier interacts with the carboxyl, alpha-amino, and Pro-(R) groups and the side chain of substrate amino acids. Based on these findings, potential photoaffinity probes of the ACC transport system have been identified.

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Robert A. Saftner

The effects of harvest-applied coating and shrink-wrap polymeric film treatments of apples [Malus ×domestica Borkh. `Gala' and Mansf. `Golden Delicious'] on volatile levels, quality attributes, respiration, and internal atmospheres after storage at 0 °C for 1 to 6 months, and during subsequent shelf life at 20 °C were investigated. Over 30 volatiles were detected, most of the identified volatiles were esters, the rest were alcohols, aldehydes, a ketone and a sesquiterpene. Shellac- and wax-based fruit coatings transiently inhibited total volatile levels in `Golden Delicious' while not affecting those in `Gala' apples during 6 months of storage in air at 0 °C. Holding fruit at 20 °C for up to three weeks following cold storage increased volatile levels with coated and nontreated fruit having similar amounts. Only shellac-coated `Golden Delicious' apples accumulated ethanol and ethyl acetate when held at 20 °C. The shrink-wrap polymeric film treatment had no effect on fruit volatile levels during cold storage or during subsequent shelf life at 20 °C. Coating but not film treatments reduced respiration and ethylene production rates that were observed upon transferring the fruit to 20 °C. Internal CO2 and ethylene levels increased and O2 levels decreased in coated fruit. The coating treatments led to better retention of flesh firmness in `Golden Delicious' but not `Gala' apples. Coating and film treatments reduced fresh weight loss in both cultivars during cold storage. The results suggest that harvest-applied coating and film treatments having relatively high permeability for CO2 and O2 and relatively low permeability for water vapor and fruit volatiles have potential for improving the storage and shelf-life qualities of `Gala' and `Golden Delicious' apples.

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Robert Saftner, Gene Lester and Judith A. Abbott

A new hybrid orange-fleshed netted melon has been bred specifically for use by the fresh-cut industry in winter. Quality characteristics of fresh-cut chunks from the hybrid were compared to those of its parental lines and to commercial cantaloupe and honeydew fruits available in winter. Female parent and hybrid chunks had higher soluble solids content (SSC) and firmness, and lower aromatic volatile concentrations versus that of the male parent. Hybrid chunks also had higher SSC (>3%) and were firmer (>5 N) than commercial fruit, and showed no appreciable differences in aromatic volatile concentrations to commercial honeydew or in surface color to commercial cantaloupe. Consumers liked the flavor, texture, sweetness, and overall eating quality of the hybrid chunks better than those of its inbred parents and winter honeydew and as well as or better than that of winter cantaloupe. Hybrid fruit stored 5 weeks at 1 °C under modified atmospheric conditions, then fresh-cut and stored 14 d in air at 5 °C maintained good quality (firmness = 51 N, SSC = 12.2%, surface pH = 6.0, beta-carotene and ascorbic acid concentrations = 14 and 182 mg·kg-1, respectively), and showed no signs of tissue translucency or surface pitting despite microbial populations approaching 8 log cfu·g-1. The results indicate that the orange-fleshed hybrid melon is a promising new melon type for fresh-cut processing, especially during the winter.

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Robert A. Saftner*, Judith A. Abbott and Gene E. Lester

New fresh-cut melon products prepared from orange-fleshed honeydews have recently become available in retail markets. We compared fresh-cut chunks of orange-fleshed honeydew (`Temptation' and four breeding lines), green-fleshed honeydew (`Honey Brew'), and cantaloupe (`Cruiser'). All genotypes had similar respiration and ethylene production rates and soluble solids contents: genotype means for soluble solids contents were between 9.4% and 10.1 %. Five hundred untrained consumers preferred the flavor, texture, and overall eating quality of the orange honeydews to the green cultivar, with `Temptation' scoring highest. `Temptation' chunks were less firm at the time of processing and after 12 days storage than chunks prepared from all other genotypes. The color of orange-fleshed honeydew chunks was intermediate between that of cantaloupe and green-fleshed honeydew and the color was maintained during 12 days storage. Total aromatic volatiles from juice extracts of orange-fleshed honeydew chunks was 1.2 to 4.7 times higher than that of green-fleshed honeydew extracts and volatiles from cantaloupe was >4.8 fold greater than extracts from `Temptation' and >9.3 fold higher than that of other honeydew extracts. Many individual volatiles were identical in cantaloupe and honeydews; however, honeydew genotypes, particularly the orange-pigmented types, were distinctive from cantaloupe in having relatively high levels of various nonenyl and nonadienyl acetates of uncharacterized aromas. The results indicate that `Temptation' and other orange-fleshed honeydews are a promising new melon type for fresh-cut processing.

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John R. Stommel, Judith A. Abbott and Robert A. Saftner

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Robert A. Saftner, William S. Conway and Carl E. Sams

Changes in tissue water relations, cell wall calcium (Ca) levels and physical properties of Ca-treated and untreated `Golden Delicious' apples (Malus×domestica Borkh.) were monitored for up to 8 months after harvest. Pressure infiltration of fruit with CaCl2 solutions at concentrations up to 0.34 mol·L-1 reduced both fruit softening and air space volume of fruit in a concentration-dependent manner. Turgor potential-related stress within the fruit persisted during storage and was higher in Ca-treated than in untreated fruit. Fruit that were pressure infiltrated with CaCl2 solutions between 0.14 and 0.20 mol·L-1 and then waxed to reduce water loss during storage showed no peel injury. Calcium efflux patterns from apple tissue disks indicated two distinct Ca compartments having efflux kinetics consistent with those for cell wall Donnan-phase bound and water free space soluble Ca. At Ca concentrations up to 0.20 mol·L-1, cell wall bound Ca approached saturation whereas soluble Ca showed a linear dependence. At higher external Ca concentrations, only soluble Ca in the tissue increased. During 8 months of cold storage, cell wall Ca-binding capacity increased up to 48%. The osmotic potential of apples harvested over three seasons ranged between-1.32 and -2.33 MPa. In tissue disks, turgor potential changes caused by adjusting the osmolality of the incubation solution with CaCl2 or sorbitol were accompanied by changes in the osmotic and water potentials of the tissue. In CaCl2 solutions up to 0.34 mol·L-1, turgor potential was ≥0.6 MPa in tissue incubated in 0.14 or 0.17 mol·L-1 solutions of CaCl2 and was more than 3 times higher than in tissues incubated in low (≤0.03 mol·L-1) or high (≥0.27 mol·L-1) concentrations of CaCl2. At osmotically equivalent concentrations, turgor potential was up to 40% higher in Ca-than in sorbitol-treated tissue. The results suggest that postharvest treatment with 0.14 to 0.20 mol·L-1 solutions of CaCl2 are best for maintaining fruit water relations and storage life of `Golden Delicious' apples while minimizing the risk of salt-related injuries to the fruit. While higher concentrations of CaCl2 may better maintain firmness, these treatments adversely affect fruit water relations and increase the risk of fruit injury.

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Robert A. Saftner, William S. Conway and Carl E. Sams

Effects of postharvest pressure infiltration of distilled water, CaCl2 solutions at 0.14 or 0.27 mol·L-1 without and with subsequent fruit coating treatments of preclimacteric `Golden Delicious' [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. `Golden Delicious'] apples on volatile levels, respiration, ethylene production, and internal atmospheres after storage at 0 °C for 1 to 6 months, and during subsequent shelf life at 20 °C were investigated. Over 30 volatiles were detected, most of the identified volatiles were esters; the rest were alcohols, aldehydes, ethers, a ketone, and a sesquiterpene. Pressure infiltration of water and increasing concentrations of CaCl2 resulted progressively in reduced total volatile levels, respiration, ethylene production, and internal O2 levels and increased CO2 levels in fruit following 2 to 4 months storage in air at 0 °C. Total volatile levels, respiration, ethylene production, and internal atmospheres of CaCl2-treated apples at 0.14 mol·L-1 gradually recovered to nontreated control levels following 2 weeks of shelf life at 20 °C and/or storage at 0 °C in air for more than 4 months. Following the calcium treatments with a shellac- or wax-based coating had similar but stronger and more persistent effects on volatile levels, respiration, ethylene production, and internal atmospheres than those found in fruit treated with CaCl2 alone. Calcium infiltration did not change the composition of volatile compounds found in fruit. Results suggest that pressure infiltration of `Golden Delicious' apples with CaCl2 solutions transiently inhibited volatile levels, respiration, and ethylene production, in part, by forming a more-or-less transient barrier to CO2 and O2 exchange between the fruit tissue and the surrounding atmosphere.

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James J. Polashock, Robert A. Saftner and Matthew Kramer

Fruit of highbush blueberry (Vaccinium corymbosum L.) produce antimicrobial volatiles, including trans-2-hexenal, that may confer resistance to anthracnose fruit rot, an important postharvest disease caused by Colletotrichum acutatum J.H. Simmonds. To investigate whether aromatic volatiles in highbush blueberry fruit are associated with postharvest fruit rot resistance, we compared volatiles emitted from whole fruit and extracts from fruit kept in air at 20 °C for 0 to 6 days postharvest from cultivars having a wide range of resistance to anthracnose. Antimicrobial volatiles detected included the aldehydes, trans-2-hexenal and hexanal; the monoterpenes, limonene, linalool, 8-hydroxylinalool, α-terpineol, and terpinyl acetate; and the sesquiterpenes, cadinene, caryophyllene, and α-farnesene. There were significant correlations between some detected volatiles and these differed in whole fruit and extracts. Hexanal (in fruit extracts), trans-2-hexenal, terpinyl acetate, and cadinene emissions increased in most cultivars when fruit were kept in air at 20 °C for various times postharvest. Volatile emissions from whole fruit and extracts varied widely among the cultivars with early ripening cultivars generally showing higher volatile emissions than later ripening cultivars. Although the cultivars tested differed in quantities, and in some cases, the types of volatiles produced, these differences were not related to pedigree (i.e., species composition) nor to known anthracnose resistance ratings. Except for the confounded emissions of terpinyl acetate and cadinene, more than 80% of the variation observed for each volatile was attributable to the cultivar (genetic), year (environmental), and cultivar–by-year interaction. The results suggest that, although antimicrobial aldehydes and terpenes emitted from fully ripe highbush blueberry fruit and extracts might be important flavor and aroma components, they do not significantly contribute to disease resistance against anthracnose fruit rot.

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Gene E. Lester, Robert A. Saftner and D. Mark Hodges

Orange-fleshed honey dew (Cucumis melo L., Inodorus group) fruit are known for having superior food-safety, food-quality, and fruit-marketability attributes compared with orange-fleshed netted muskmelon (C. melo, Reticulatus group) and to green-fleshed honey dew (C. melo, Inodorus group) fruit. However, little is known about the production market attributes and postharvest quality comparisons of the leading orange-fleshed honey dew cultivars. Five orange-fleshed honey dew genotypes (‘Honey Gold’, ‘Orange Delight’, ‘Orange Dew’, ‘Temptation’, and a breeding line) were glasshouse-grown in both fall and spring, harvested at abscission (full-slip), and compared after storage for 3–24 days in air at 5 or 10 °C. Fruit maturity (full-slip) was between 31 and 38 days after anthesis, with maturation dependent on genotype. Days to maturity were slightly longer in the fall than in the spring. Fruit size (number of fruit per standard commercial shipping box) was between four and six fruit per box. ‘Orange Dew’ consistently had the smallest fruit (six per box), and the breeding line had the largest (four per box). ‘Orange Delight’ and ‘Orange Dew’ had the fewest whole-fruit disorders and the highest percentage of marketable fruit at harvest and following 24 days of storage at 5 or 10 °C. ‘Orange Delight’, ‘Orange Dew’, and the breeding line consistently had a more yellow peel, whereas ‘Honey Gold’ and ‘Temptation’ fruit peels had a more greenish hue. Whole-fruit firmness was 10–25 N among the cultivars and 24–35 N for the breeding line. Internal-fruit disorders, percentage marketability, and mesocarp (pulp) firmness reflected each genotype's whole-fruit attributes. ‘Orange Delight’ and ‘Orange Dew’ fruit consistently had among the highest soluble solids concentration and relative sweetness ratings, and their pulp had a more intense orange hue and lower lightness than those of the other genotypes. After 24 days of storage, ‘Orange Delight’ and ‘Orange Dew’ maintained their higher sweetness and more orange hue in both spring and fall harvests; however, depending on harvest, they were not always significantly sweeter or more orange-hued than some of the other genotypes. Our results indicate that orange-fleshed honey dew fruit are a promising new melon type suitable as a substitute for orange-fleshed netted muskmelon fruit not only for food-safety issues but also for overall marketable quality.

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Jin-He Bai, Robert A. Saftner and Yuen S. Lee

The development of tissue translucency of fresh-cut honeydew cubes adversely affects product quality and primarily occurs in cubes that have been sanitized by dipping in chlorine water (sodium hypochlorite solution) following processing. Chlorine water dips containing calcium propionate as an antimicrobial salt were tested to decrease tissue translucency and extend the marketable shelf life of honeydew (2-cm cubes) sealed in a rigid container with a film overlap and stored at 10 °C for 7 days. Honeydew cubes not dipped following processing had higher respiration rates and microbial populations than cubes that had been dipped, and lost their marketability on day 5 due to off-odor development. Dipping in chlorine water decreased the initial population and growth of microorganisms on the cubes, compared to dipping in water or not dipping. However, translucency developed in cubes dipped in water, with or without chlorine, and became unsalable by day 5. Chlorine water dips containing calcium propionate were devised that maintained excellent antimicrobial characteristics and prevented translucency in honeydew cubes kept 7 days at 10 °C. Quality analyses revealed that calcium propionate treatments decreased respiration and ethylene production rates, maintained tissue firmness, the lightness and brightness of cube surfaces, melon aroma and overall visual quality through 7 days of storage. The calcium propionate dips did not impart or induce any detectable off-flavors or off-odors to the cubes.