Packaged salad-cut lettuce for food service and salad mixes is an increasingly important component of the lettuce industry (Glaser et al., 2001). Lettuce is highly perishable, and the cutting required in processing further shortens its shelf life (Bolin and Huxsoll, 1991). Modified-atmosphere (MA) packaging, in conjunction with temperature control, have been important techniques for extending the shelf life of these products (Kim et al., 2005; Smyth et al., 1998). Typically, low-O2/high-CO2 environments are created that will retard oxidative browning and delay senescence (Kim et al., 2005; Smyth et al., 1998). These environments are achieved by matching product respiration with the oxygen permeability of the packaging film, and by flushing the package with a low O2 gas mixture to rapidly achieve the desired gas environment. Although this achieves control of browning, damage from CO2 injury or fermentation from low O2 stress may reduce the salability of the product (Kim et al., 2005; Smyth et al., 1998).
Shelf life and the visual quality of salad-cut lettuce can be affected by the production environment, vegetative maturity, as well as by the choice of cultivar (Chiesa et al., 2003; Couture et al., 1993; Watada and Qi, 1999). Furthermore, lettuce breeders seek to develop multiuse cultivars that are useful in a diversity of products and markets. However, little if any breeding has been reported on the shelf life of salad-cut lettuce in MA packaging. Given the importance of this market, lettuce cultivars, breeding lines, and populations should be selected with increased shelf life in low-O2/high-CO2 MA environments. To implement this practice, effective evaluation methods and knowledge of the genetic variation within lettuce for shelf life are needed. The objectives of this research were to determine the genetic variation for shelf life of salad-cut lettuce in low-O2 MA environments and to develop rapid evaluation methods suitable for a lettuce breeding program.
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