The continuous development of improved snap bean cultivars throughout the years has provided germplasm with wide variety of colors, textures, shapes, and sizes to meet the growing conditions and taste preferences of consumers from many different regions (Orzolek et al., 2000). In 2001, the collection of the Food and Agriculture Organization included 26,500 Phaseolus vulgaris entries, reflecting a large genetic diversity (CIAT, 2001). Such diversity can explain the wide variation in shelf life, resistance to chilling temperatures as well as variability in physical and chemical attributes. Generalization of sensory and compositional attributes among snap bean cultivars is difficult. Quality differentiation among individual fruits and vegetables by consumers is based primarily on appearance (Zind, 1989). In snap beans, color is an important feature, which changes from a desirable bright green to an objectionable yellowish color (Trail et al., 1992). Textural attributes and loss of chlorophylls are also excellent indices of quality because they parallel color changes, loss of ascorbic acid, and off-flavor development (Cain et al., 1953; Martinez et al., 1995).
Quality at harvest and environmental conditions, particularly temperature, during the postharvest period greatly affect the shelf life and quality of snap beans. It is well recognized that good temperature management is the simplest way to maintain a high-quality appearance as well as to delay losses in the nutritional value of fruits and vegetables in general (Nunes, 2008a; Nunes and Emond, 2002). As a result of their high respiration rate and sensitivity to chilling temperatures, snap beans are very perishable (Costa et al., 1994). Therefore, for a maximum shelf life of 8 to 12 d, recommended storage temperatures range from 5 to 7.5 °C with 95% to 100% relative humidity (Cantwell and Suslow, 2010; Hardenburg et al., 1986). When stored at temperatures above the recommended, snap beans will show discoloration, yellowing, loss of firmness, and a leathery appearance, whereas when stored at temperatures below the recommended, the pods will develop chilling injury (CI) symptoms such surface pitting, diagonal brown streaks, dull appearance, and breakdown from microorganisms after transfer to warm temperature (Nunes, 2008a; Watada and Morris, 1966b). However, sensitivity to chilling temperatures seems to be cultivar-dependent (Watada and Morris, 1966a). In addition to good temperature management, minimizing the time between harvest and sale prevents decrease in chlorophylls and vitamin C contents, increased weight loss resulting from loss of moisture, and reduced crispness (Sistrunk et al., 1989).
Much of the research work done on snap beans has been directed to the processing industry (Ferreira et al., 2006; Freeman and Sistrunk, 1978; Gould et al., 1951; Kahn and McGlynn, 2009; Woodruff et al., 1962) with a few recent studies on fresh produce (Cano et al., 1998; Costa et al., 1994; Kahn and McGlynn, 2009; Martinez et al., 1995; Nunes et al., 2001). No data were however found in the literature regarding quality curves for snap beans stored at various temperatures. In fact, the few previous published studies report the optimum storage temperature for snap beans (Monreal et al., 1999; Trail et al., 1992) or the response to storage at chilling temperatures (Abou Aziz et al., 1976; Gorini et al., 1974; Watada and Morris, 1966a, 1966b) rather than changes in quality that develop over time and over a wide range of temperatures. In addition, previous studies have shown that the quality attributes that limit shelf life may vary depending on the commodity and storage temperature and therefore one single attribute should not be used to determine the end of the shelf life of a particular fruit or vegetable (Nunes et al., 2004, 2007; Proulx et al., 2005). Yet again, no information was found regarding the most important sensory quality attributes that determine the limits of marketability for snap beans stored at various temperatures. Finally, although the sensory quality of a specific commodity may still be considered acceptable for sale or consumption, the remaining compositional value might have been already significantly reduced.
The objectives of this work were to: 1) create quality curves for snap beans stored at chilling and non-chilling temperatures; 2) identify which sensory quality attribute limits the shelf life and marketability of snap beans when stored at chilling and non-chilling temperatures; and 3) evaluate the remaining compositional value at the point the snap beans had reached the minimum acceptable quality for sale.
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