immediate transport to market and the firmer fruit headed to storage. Systems that sort by color such as with apple (Malus × sylvestris var. domestica) (Tao et al., 1995) might be useful if fruit color can be accurately determined, as green color intensity declines as fruit ripen in some genotypes (McGrath and Karahadian, 1994). However, green color intensity must first be closely correlated to ripening stage across cultivars.
Pawpaw fruit soften rapidly at room temperature after harvest. McGrath and Karahadian (1994) and Layne (1996) indicated a 2-to-3-d shelf life was to be expected, although we have observed that those fruit at the earliest stage of ripening may have a 5-to-7-d shelf life. Refrigeration is a likely solution for slowing the loss of firmness and short-term storage. Cherimoya suffer chilling injury at temperatures below 7 °C (44.6 °F) (Alique et al., 1994). However, we have observed that pawpaw fruit can be stored for 1 month at 4 °C with little change in fruit firmness and apparently continue normal ripening upon removal to ambient temperature. We say apparently because not all ripening traits were evaluated, nor were post-storage taste tests performed. The optimum temperature and duration for holding the fruit will need to be determined. A 4- to 8-week cold-storage period after harvest could help with an orderly marketing schedule. Combined with a range of harvest periods from different cultivars, the season could be extended from the current 4 to 6 weeks now to 8 to 12 weeks. Further extension in pawpaw storage life may be feasible with controlled or modified atmosphere storage (Thompson, 1996).
Regardless of the method and details of storage, the quality of fruit ripened after cold storage must be consistent with that which occurs without storage. This is true not only for the continuing decline in firmness but the development of flavor and soluble solids content as well. The flavor of pawpaw fruit is very distinctive and needs to be preserved for the consumer.
There are a number of practical problems with pawpaw harvest and postharvest storage. A greater understanding of pawpaw ripening physiology and the role of ethylene in coordinating the process is needed. The solutions to the current problems may mean applying common harvest and storage techniques from other tree fruit crops to pawpaw. Many techniques need to be assessed to identify those most applicable to extending pawpaw storage life while maintaining high fruit quality. We are currently studying these problems and assessing potential solutions. With good fortune there may be recommendations for pawpaw harvest and handling in the near future.
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