Annual consumption of fresh plums in the United States is 0.6 lb per capita, which is lower than that of similar types of fruit such as sweet cherry (Prunus avium) and peach (Prunus persica) that have an annual per capita consumption of 1.1 and 2.8 lb, respectively (U.S. Department of Agriculture, 2017). Low consumption may be due to the lower quality that occurs with harvest at an early stage of fruit maturity, a necessary practice to prevent bruising and premature ripening during long-distance shipping. Producers harvest plums when flesh firmness reaches 10 lbf, but plums are not considered ready to eat until they soften to 2–3 lbf (Crisosto, 1994; Kader and Mitchell, 1989; Robertson et al., 1992). Harvesting plums at more advanced stages of maturity can improve fruit quality and consumer acceptance but leads to a reduction in shelf life and greater potential for damage during shipping and distribution (Abdi et al., 1997; Candan et al., 2008; Crisosto et al., 2004; Fajt and Usenik, 2010). By growing plums closer to their intended market, they can be marketed without the need for long-distance shipping, which allows growers to harvest them at a later stage of maturity when quality is optimal.
To create cultivars with improved fruit quality, the asian plum has been hybridized with the apricot plum (Prunus simonii), the myrobalan plum (Prunus ceracifera), and other species and for cold temperature tolerance, it has been hybridized with american and canadian plum (Prunus nigra) (Hansen, 1915; Okie and Ramming, 1999). This has resulted in interspecific plums derived from the asian plum that are referred to as asian or japanese plums, and american plum (Table 1). European plums with sufficient cold temperature tolerance can be an option in zones 4 and 5 but differ in texture, flavor, and appearance from asian and american plums and are relatively unknown to most consumers. The asian plums ‘Shiro’ and ‘Methley’ are grown for their consistently high yield in cold regions but knowledge on the consumer acceptance of these and other cold hardy plums needs further evaluation. Cultivation of plums in eastern and northern growing regions of the United States and Canada requires cultivars that possess cold temperature tolerance, resistance to bacterial leaf spot, and rain cracking resistance (Norton et al., 1987), but these traits are not typically present in asian cultivars selected for long-distance shipping.
Plum and plum hybrid cultivars evaluated in this study and their respective type and species.
Consumer preference depends on flavor, texture, and appearance, which vary with cultivar and maturity at harvest (Boyhan et al., 1996; Corollaro et al., 2014; Crisosto et al., 2003). These traits can be measured with sensory testing using the untrained general public and a hedonic liking scale from 1.0 to 9.0 (Peryam and Pilgrim, 1957). For plums sold in supermarkets, a hedonic degree of liking score greater than 5.0 (neither like nor dislike) is considered consumer accepted (Crisosto et al., 2004). However, minimum acceptability scores as low as 5.0 could potentially lead to cultivar recommendations that have only slightly positive ratings of liking (Meredith et al., 1992). To ensure successful marketing, food products are expected to score at least 7.0 (Stone et al., 2012).
Soluble solids concentration, titratable acidity (TA), and flesh firmness are commonly used as indirect measures of fruit quality. Consumer acceptance of plums tends to be more favorable as SSC increases from below 10% to above 14%, but TA becomes important when SSC is below 12% (Crisosto et al., 2004). Most of the commercially important cultivars emit low amounts of aroma volatiles (Gómez and Ledbetter, 1994), so sweetness and sourness contribute most to plum flavor (Singh and Singh, 2008) and consumer acceptance (Crisosto et al., 2003). However, these traits are not as well characterized in american plums. Texture is not well studied in plums but has an impact on acceptability of sweet cherry (Chauvin et al., 2009), peach (Olmstead et al., 2015), and northern highbush blueberry [Vaccinium corymbosum (Gilbert et al., 2014)]. Many factors in addition to sweetness, sourness, and firmness contribute to fruit quality such as aroma, bitterness, astringency, and juiciness for which optimum ranges are not yet established. Because of the complex nature of quality, consumer testing is needed to identify cultivars with high consumer appeal. The objectives of this research were to determine if the partially ripe stage of maturity is as acceptable as the tree-ripe stage of maturity in several asian plum cultivars and to determine the consumer acceptability of three plum types that possess cold hardiness in U.S. Department of Agriculture hardiness zone 5.
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