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.
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.
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.
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.
`Golden Delicious' apples were pressure-infiltrated (34 kPa) at harvest with 0, 20, 35, or 50 g·L–1 solutions of CaCl2 followed without and with a water rinse, a wax or shellac emulsion treatment, or a shrink-wrap packaging, and stored at 0°C. The CaCl2 treatments delayed senescent breakdown, but also caused superficial injury to the fruit. A water rinse in combination with a wax- or shellac-based coating or shrink wrap packaging reduced the appearance of superficial injury in fruit treated with 35 or 50 g·L–1 solutions of CaCl2 and eliminated it in fruit treated with a 20 g·L–1 solution of CaCl2. While reducing the risk of calcium-related injury to the fruit, the coating and film treatments maintained the beneficial effects of calcium on apples and reduced weight loss of the fruit during cold storage.
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.
Three polyamine biosynthesis inhibitors, α-difluoromethylornithine (DFMO), α-difluoromethylarginine (DFMA), and α-methylornithine (MeOrn), alone and in combination with CaCl2, were tested for their ability to reduce in vitro growth and soft rot development in apple (Malus domestica Borkh.) fruit caused by Botrytis cinerea Pers.:Fr. and Penicillium expansum Link. All three inhibitors reduced the in vitro growth of the pathogens. Calcium had no effect on fungal growth in vitro. Pressure infiltration of millimolar concentrations of DFMO or DFMA or 25 g·L-1 CaCl2 solutions into apples reduced subsequent soft rot development by B. cinerea and P. expansum >40%. A combination treatment of Ca and DFMO or DFMA reduced decay >67%. Treatment of apples with MeOrn was less effective at inhibiting decay development. None of the inhibitors affected polyamine levels in apple cortical tissues. Some injury to the fruit surface was observed with Ca treatments. Fruit treated with Ca and any of the inhibitors were less firm than those treated with Ca alone. Specific polyamine biosynthesis inhibitors in combination with Ca may prove useful in reducing postharvest decay in apples.
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.
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.