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Jong-Pil Chun, Jae-Chang Lee, and Yong-Soo Hwang

Pectins isolated from three cultivars with different maturity were compared to find a potential role of pectin modification on the fruit softening during fruit development and ripening. There was an increase of total pectins in developing fruit and no significant decrease of pectins was confirmed even after storage in `Tusgaru' (30 days) and `Fuji' (120 days), whereas soluble pectins, except NaOH-soluble ones, gradually increased in all cultivars. Gel-filtration profile and ion exchange chromatographic evidence of soluble pectins revealed that pectin degradation in apple fruit may not be associated with softening. However, a degree of esterification probably has an important role on softening of fruits. Further results will be discussed in the presentation.

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

The irradiation of harvested fruit is typically accompanied by excessive tissue softening, a process that is not well understood. In this study, we examined the role of specific cell wall polymers and the extent of general cell wall degradation and softening in irradiated tomato fruit. `Sunny' tomato fruit at mature-green and pink stages were subjected to X-ray radiation at 0, 83, and 156 Krad. Immediate softening was noted for both maturation classes, although some postirradiation recovery was evident in green fruit. Pectic polymers of both mature-green and pink fruit exhibited depolymerization and altered neutral sugar profiles in response to irradiation. Pectins, either as components of total ethanol-insoluble solids (EIS), purified by selective extraction, or of commercial origin were similarly affected by irradiation. Cellulose preparations were unaffected by irradiation. The data demonstrate that the effect of irradiation on the cell wall exhibits specificity, can occur nonenzymatically, and does not require initiating adducts of cytosolic origin.

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Raymond G. McGuire and Guy J. Hallman

Harvested, mature-green guava (Psidium guajava L.) fruit were coated with cellulose- or carnauba-based emulsions to compare the effect on fruit ripening and quality of ripened fruit. Coatings containing 2% or 4% hydroxypropylcellulose significantly slowed softening an average of 35% or 45%, respectively, compared to uncoated fruit (a delay of 1 to 2 days in September and 4 to 5 days by January). A 5% carnauba formulation slowed softening by 10% to 30% and was most effective at reducing weight loss. Neither of the cellulose- nor the carnauba-based coatings affected the decay susceptibility of softened fruit, but coated fruit did not develop as much color, had a lower soluble solids concentration, and were more prone to surface blackening in storage than uncoated fruit.

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Marcelo A.G. Carnelossi, Edinaldo O.A. Sena, Adrian D. Berry, and Steven A. Sargent

( Sreedharan et al., 2015 ). Pulp firmness, SSC, pH, and titratable acidity. Regardless of the cooling method, blueberry firmness was higher after 7 d (‘Farthing’) and 14 d (‘Emerald’) of storage, then fruit gradually softened ( Table 1 ). For ‘Farthing

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Douglas D. Archbold, Rumphan Koslanund, and Kirk W. Pomper

To facilitate the growth of a commercial pawpaw (Asimina triloba) industry, several problems with harvest and postharvest handling of fruit need to be resolved. Pawpaw fruit ripening is characterized by an increase in soluble solids content, fl esh softening, increased volatile production, and a loss of green color intensity. Within 3 days after harvest, ethylene and respiratory climacteric peaks are clearly evident. Softening of fruit is due to the action of at least four enzymes, with the softening proceeding from the surface to the interior tissue. Fruit on a single tree can ripen over a 2-week period, creating labor problems. When immature fruit is harvested it does not ripen, even if treated with ethephon at 1000 mg·L-1 (ppm), but the use of commercially available growth regulators both pre- and postharvest warrants further study. Fruit soften very rapidly at room temperature after harvest and have a 2-to 4-day shelf life. However, we have stored pawpaw fruit for 1 month at 4 °C (39.2 °F) with little change in fruit firmness and fruit apparently continue normal ripening upon removal to ambient temperature. The optimum temperature and duration for holding fruit will need to be determined. Further extension in pawpaw storage life may be feasible with controlled or modified atmosphere storage. Although there are a number of practical problems with pawpaw harvest and postharvest storage that need to be addressed, we hope to develop recommendations for harvest and handling of fruit in the near future.

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Donald J. Huber and Ken C. Gross

The absence of endo-α-1,4-d-galacturonanase (PG, EC in some fruits and the molecular suppression of PG in tomato fruit have collectively provided evidence that this protein is neither required nor sufficient to achieve normal softening in fleshy fruits. On the other hand, initial claims that down-regulation of PG was without effect on tomato softening were overstated. The influence of PG on softening does appear to be minimal during the initial stages of ripening, during which time changes in the locule tissues can significantly alter texture as monitored in whole fruit. Enzymes, including pectinmethylesterases, cellulases, rhamnogalacturonanase, and glycosidases may also play pivotal roles in softening. β-galactosidases have attracted much attention as potential determinants of fruit texture; however, conclusive evidence for this role is lacking, and increased levels of β-galatosidase (and net cell wall galactosyl residue loss) have been noted in senescing vegetative and floral organs as well as in fruit. Apoplastic pH, ionic activity, and composition are likely to contribute to tissue and wholeorgan texture through weakening of polymer aggregates and/or through modulation of cell wall enzyme activity. During the latter stages of ripening and overripening, the role of PG is apparent from the persistent structural integrity of fruit transformed with PG antisense constructs. Patterns of softening and deterioration in normal tomato fruit suggest that the catalytic activity of PG in vivo is initially queued and does not parallel the accumulation of PG protein. Developmental changes in membrane permeability, physical injury, and other stress conditions can alter the apoplastic environment, releasing constraints on PG action.

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Fan-Hsuan Yang, David R. Bryla, and Bernadine C. Strik

, 2012 ). The final type of heat damage observed was poor coloration during ripening ( Fig. 4F ). Berries with this type of damage tended to be smaller and less blue at maturity than other berries on the same cluster. Blueberries may also soften

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Kanti M. Rawal and Keith Redenbaugh

Polygalacturonase (PG) is the principal enzyme responsible for the softening of tomato during ripening. Transformation of tomatoes with antisense PG (asPG) results in significant delay in softening so that fruits with color and flavor can be harvested and shipped from the fields to distant markets. Safety evaluations of the genetically engineered tomato varieties were conducted from two perspectives: a) agricultural, and b) human food. Data were submitted to the appropriate agencies to obtain approvals for commercial production and to seek advisory opinion for the safety of food for human consumption. Calgene Fresh Inc. was created to develop human resources, physical facilities and logistic capabilities for year round supply of high quality branded produce. Vertical integration from seed production to direct consumer marketing is necessary to optimize the business endeavor.

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Yufei Xu*, Eric Hanson, James Flore, and Wayne Loescher

In Michigan boron (B) deficiencies in sour cherry have resulted in routine use of B sprays to enhance fruit set and increase fruit yield. However, field observations indicate that high B levels are associated with premature softening, making fruit unacceptable for processing. Our fertilization studies show that fruit B levels are higher, but B generally has little or no effect on fruit size, maturity, color, or pull force. However, at some locations, B applications increase the number of soft fruit, especially when harvest is delayed well after the optimum maturity date (as indicated by pull force). B-induced yield increases can be achieved without inducing excessive fruit softening by careful monitoring of fruit maturation and prompt harvest. Leaf and fruit B levels will be presented.

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Mario Mandujano, F.G. Dennis Jr., D.E. Guyer, E. Timm, and G.K. Brown

Michigan growers often have severe problems with soft `Montmorency' sour cherries. Causal factors may include weather conditions, orchard practices, harvesting methods, and conditions during hold of fruits prior to processing. In this study, efforts were concentrated on orchard practices, including shading to reduce solar radiation, irrigation, nutrient level, and application of growth regulators, especially ethephon and gibberellin. Fruit firmness decreased as maturity approached, then stabilized. Significant fruit softening occurred only during mechanical harvesting. No treatments, including sprays of calcium and potassium, consistently increased firmness, but firmness was reduced in 1993 by spraying with ethephon. Firmness varied among orchards, but no “soft” fruit, as defined by industry standards, were observed in harvested fruit. Softening appeared to be caused by excessive bruising, and was always associated with mechanical damage. Advanced maturity and heavy cropping appear to predispose the cherries to greater bruise damage.