Flesh softening is a major cause of deterioration in kiwifruit limiting storage life (MacRae and Redgwell, 1992) and affecting consumer acceptability (Stec et al., 1989). Kiwifruit firmness declines rapidly after harvest and is reduced to almost half of the initial value within 4 weeks of storage at 0 °C in air (Benge et al., 2000). Kiwifruit is particularly sensitive to ethylene, a hormone implicated in the softening process. Concentrations of ethylene as low as 0.005 to 0.01 μL·L−1 are sufficient to hasten kiwifruit softening and to limit its storage life and marketability (Crisosto et al., 2000).
The ethylene action inhibitor 1-methylcyclopropene (1-MCP) is an effective tool to reduce the negative effects of ethylene in fruits, vegetables, and ornamentals (Blankenship and Dole, 2003). Slower softening rates, higher acidity, and lower emission of flavor volatiles are general effects of 1-MCP observed in several fruit types (Blankenship and Dole, 2003; Watkins, 2006). Applied to kiwifruit immediately after harvest, 1-MCP reduces respiration rate, ethylene production, flesh softening, color development, and decay (Kim et al., 2001; Koukounaras and Sfakiotakis, 2007). 1-MCP has little or no effect on soluble solids content, but titratable acidity is generally higher in 1-MCP-treated kiwifruit (Koukounaras and Sfakiotakis, 2007). When applied to kiwifruit after a period (30 d) in cold storage, 1-MCP is also effective in reducing subsequent softening during shelf life at 20 °C (Boquete et al., 2004), but the treatment becomes less effective after longer periods in cold storage. For example, Kim et al. (2001) observed no reduction in softening during shelf life when kiwifruit were treated with 1-MCP after 32 d in cold storage.
Firmness is an important quality attribute by itself, and it also affects the perception of kiwifruit flavor (Stec et al., 1989). For this reason, technologies aiming at reducing the softening rate of kiwifruit should be evaluated for their effects on other sensory attributes. Despite its beneficial potential as a postharvest treatment to control excessive softening, it is not clear how 1-MCP affects the sensory properties of kiwifruit. Harker et al. (2008) reported that a consumer panel was unable to distinguish between 1-MCP-treated kiwifruit and untreated controls; however, the effects of 1-MCP on firmness are significant (Kim et al., 2001; Koukounaras and Sfakiotakis, 2007) and likely to interact with the perception of other attributes (Stec et al., 1989). In addition to the effect on firmness, 1-MCP affects other kiwifruit attributes with sensory implications: increased acidity, delayed color changes, and lack of aroma (Boquete et al., 2004; Koukounaras and Sfakiotakis, 2007).
The objectives of this study were to evaluate the effect of 1-MCP on some quality traits linked to sensory attributes of kiwifruit after storage periods ranging from short to long term and to assess whether 1-MCP-treated fruit can be conditioned to recover their sensory properties.
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