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R.E. McDonald, T.G. McCollum, and E.A. Baldwin

Mature, green tomatoes were either gassed or not gassed with C2H4 for 24 h, immersed in 42C water for 60 min, or held in 38C air for 48 h or not treated, and then stored at either 2C or 13C for 14 days before ripening at 20C. During ripening, the fruit were evaluated for color development, internal quality, and decay and for volatiles when full ripe. Both high-temperature treatments reduced chilling injury and inhibited decay. Days to ripen after removal from storage at 2C or 13C was not influenced by heat treatment method. Color development, lycopene content, and internal quality characteristics of fruit were similar at the ripe stage, irrespective of heat treatment. Of 15 volatiles analyzed, seven showed decreased levels of concentrations as a result of C2H4 gassing, nine showed decreased levels when stored at 2C prior to ripening, and most were unaffected by the heat treatments. Heat treatments appear to be beneficial for maintaining tomato fruit quality.

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M.M. Peet

The environmental and physiological causes of cracking or splitting of soft fruits and citrus as they ripen are not well understood. This paper explores factors contributing to radial cracking in tomatoes, gives suggestions for prevention of cracking, and suggests directions for future research. Fruit cracking occurs when there is a rapid net influx of water and solutes into the fruit at the same time that ripening or other factors reduce the strength and elasticity of the tomato skin. In the field, high soil moisture tensions suddenly lowered by irrigation or rains are the most frequent cause of fruit cracking. Low soil moisture tensions reduce the tensile strength of the skin and increase root pressure. In addition, during rain or overhead irrigation, water penetrates into the fruit through minute cracks or through the corky tissue around the stem scar. Increases in fruit temperature raise gas and hydrostatic pressures of the pulp on the skin, resulting in immediate cracking in ripe fruit or delayed cracking in green fruit. The delayed cracking occurs later in the ripening process when minute cracks expand to become visible. High light intensity may have a role in increasing cracking apart from its association with high temperatures. Under high light conditions, fruit soluble solids and fruit growth rates are higher. Both of these factors are sometimes associated with increased cracking. Anatomical characteristics of crack-susceptible cultivars are: 1) large fruit size, 2) low skin tensile strength and/or low skin extensibility at the turning to the pink stage of ripeness, 3) thin skin, 4) thin pericarp, 5) shallow cutin penetration, 6) few fruits per plant, and 7) fruit not shaded by foliage. Following cultural practices that result in uniform and relatively slow fruit growth offers some protection against fruit cracking. These practices include maintenance of constant soil moisture and good Ca nutrition, along with keeping irrigation on the low side. Cultural practices that reduce diurnal fruit temperature changes also may reduce cracking. In the field, these practices include maintaining vegetative cover. Greenhouse growers should maintain minimal day/night temperature differences and increase temperatures gradually from nighttime to daytime levels. For both field and greenhouse tomato growers, harvesting before the pink stage of ripeness and selection of crack-resistant cultivars probably offers the best protection against cracking. Areas for future research include developing environmental models to predict cracking and exploring the use of Ca and gibberellic acid (GA) sprays to prevent cracking.

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P. Perkins-Veazie, J.K. Collins, and B. Strik

Harvesting raspberry fruit with an attached receptacle prevents compression of the fruit in storage containers and permits harvesting of immature fruit. This study was done to determine the effects of receptacle retention on fruit quality during storage. `Heritage' raspberry fruit from Oregon and Arkansas were harvested at light red (red ripe) and dark red stages of maturity, and stored at 2C, 95% RH for 7 days. Dark red fruit with receptacles were firmer than those without receptacles, but there were no differences in light red fruit. Ethylene production was higher from raspberries stored with receptacles. Total anthocyanin increased in all fruit after storage and was slightly higher in fruit without receptacles. Soluble solids concentration did not change but titratable acidity decreased during storage for all treatments. When fruit were harvested after several days of rain, decay incidence in fruit held with receptacles increased. Harvesting raspberries with attached receptacles did not increase postharvest fruit quality.

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Ann M. Callahan and Carole L. Bassett

NADP-dependent Malic Enzyme (NADP-ME, EC catalyzes the decarboxylation of malate, resulting in the release of CO2. In C3 plants the enzyme does not contribute CO2 directly to photosynthesis. Rather, it is associated with the supplemental synthesis of glycolytic and Krebs Cycle intermediates, although it may also be involved in regulating intracellular pH. NADP-ME activity increases during ripening of several fruits e.g. tomato and apple, usually in association with increased respiration of the developing fruit. We examined expression of NADP-ME during ripening in peach using a cDNA probe derived from F. trinervia (C4 dicot). The probe hybridized to a single RNA species of the predicted size and was low in abundance as expected for a C3 NADP-ME. As fruit matured, the RNA levels increased to a maximum around 133-140 days after bloom (fully ripe). NADP-ME RNA was not detectable from leaves isolated at the same time.

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N. El-Assi, D. J. Huber, and J. K. Brecht

The use of irradiation to increase longevity and quality of horticultural commodities often results in undesirable softening. The biochemical basis of irradiation-induced softening is not well understood. In this study, we investigated the role of the pectic polysaccharides in irradiation-induced textural changes of `Sunny' tomato fruit. `Sunny' mature-green and pink fruit subjected to 84 or 240 Krad experienced a dosage-dependent decrease in firmness, an increase in electrolyte leakage, and an increase in chelator-soluble pectins. Additionally, pectins prepared from 240 Krad-irradiated fruit were of markedly lower mol wt compared to those from nonirradiated fruit. Irradiation-induced downshifts in pectin mol wt were also noted for preripe fruit that lack PG activity. Mol wt decreases noted for pectins from 240 Krad-treated fruit exceeded those observed for fully ripe, nonirradiated fruit The role of other cell wall polymers in irradiation-induced textural changes is currently being addressed.

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Marcos D. Ferreira, Jeffrey K. Brecht, Steven A. Sargent, and Craig K. Chandler

Hydrocooling was evaluated as an alternative to forced-air cooling for strawberry (Fragaria × ananassa) fruit. `Sweet Charlie' strawberries were cooled by forced-air and hydrocooling to 4 °C and held in different storage regimes in three different trials. Quality attributes, including surface color, firmness, weight loss, soluble solids, and ascorbic acid content, pH and total titratable acidity, were evaluated at the full ripe stage. Fruit hydrocooled to 4 °C and stored at different temperatures for 8 or 15 days showed overall better quality than forced-air cooled fruit, with significant differences in epidermal color, weight loss, and incidence and severity of decay. Fruit stored wrapped in polyvinylchloride (PVC) film after forced-air cooling or hydrocooling retained better color, lost less weight, and retained greater firmness than fruit stored uncovered, but usually had increased decay. There is potential for using hydrocooling as a cooling method for strawberries.

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Erik J. Sacks and Douglas V. Shaw

Color change in fresh, ripe strawberry (Fragaria ×ananassa Duch.) fruit stored at 0C for up to 7 days was recorded using the Commission Internationale de l' Éclairage color space (L*, a*, and b*). External (skin) fruit color became darker and less chromatic but did not change hue. Internal (flesh) fruit color became darker and more chromatic. Regression coefficients calculated for individual genotypes were homogeneous for each of the color traits except internal hue. Depending on genotype, the red fruit flesh either became a bluer red or did not change hue. In all cases, rates of change were small. Color change for fresh strawberry fruit during several days of storage at 0C likely is not an appreciable source of error in plant breeding experiments.

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Mervyn C. D'Souza, Morris Ingle, and Suman Singha

Lycopene is the predominant carotenoid pigment in tomatoes and primarily responsible for red color. Spectrophotometric procedures for lycopene evaluation although accurate are time consuming and destructive. The objective of this study was to relate chromaticity values (L*,a*,b*) measured using a Minolta Chroma Meter CR-200b portable tristimulus calorimeter with lycopene concentrations in the pericarp of 'Celebrity', 'Mountain Delight' and 'Early Pick' tomatoes. Fruit were selected to encompass varying maturities from green to red ripe and were obtained from a commercial source. Lycopene from individual skin disks or pericarp plugs corresponding to each location of color measurement was extracted in acetone and measured spectrophotometrically at 503 nm. The L* value (a measure of lightness) or a* value (a measure of redness) was determined to be well correlated with lycopene concentration in all 3 cultivars. The linear regression of the lycopene concentration on the ratio of (a*/b*) provided the best R for all cultivars (0.75).

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J. Liu, C. Stevens, V.A. Khan, J.Y. Lu, C.L. Wilson, O. Adeyeye, M.K. Kabwe, L. Pusey, E. Chalutz, T. Sultana, and S. Droby

The application of low hormetic low-dose ultraviolet light (WV-C, 254 nm) on fruits and vegetables to stimulate beneficial responses is a new method for controlling storage rots and extending the shelf-life of fruits and vegetables. The present study was aimed at treating tomatoes (lycopersicon esculentum) with different UV-C dosages (1.3 to 40 KJ/m2) to induce resistance to black mold (Alternaria alternata), gray mold (Boytris cinerea), and Rhizopus soft rot (Rhizopus stolonifer). Thesediseases were effectively reduced when tomatoes were artificially inoculated following UV-C irradiation UV-C treated tomatoes were firmer in texture and less red in color than the control tomatoes, indicating a delay in ripening. Slower ripening and resistsace to storage rots of tomatoes are probably related. The positive effect of UVC on tomatoes decreased as treatments were performed at stages of increased ripeness.

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William C. Mitchell and Gojko Jelenkovic

Assays of enzyme activity, in vivo inhibition studies and the developmental analysis of strawberry (Fragaria × ananassa Duch.) fruit alcohol dehydrogenases (ADH) suggest that both the NAD-(E.C. and the NADP-dependent (E.C. forms of ADH enzymes play integral roles in the development and ripening of fruits. One role of ADH enzymes appears to be the evocation of changes in sugar, soluble solids, acidity and volatile compounds necessary for the normal organoleptic character of strawberry fruits. The data presented includes: 1.) The wide substrate specificity of both ADH enzymes for the “fragrance and flavor alcohols and aldehydes” synthesized by ripe strawberry fruits, 2.) the effect of inhibitors of ADH activity upon strawberry fruit ripening, and 3.) the comparative regulation of NAD- and NADP-ADH enzymes including 4.) the developmental control of ADH enzymes in strawberry fruits.