Longan (Dimocarpus longan Lour.) is a subtropical fruit of the Sapindaceae originating from Burma to southern China (Nakasone and Paull, 1998; Tongdee, 1997). The fruit has a thin, light brown rind surrounding a sweet, white aril with a black seed. Longans are a rich source of vitamin C, minerals, and bioactive polyphenols (Wall, 2006; Yang et al., 2010). Important production areas are Southern China, Thailand, Taiwan, and Australia (Nakasone and Paull, 1998). Longan is grown in Hawaii, where production has expanded rapidly following the decline of the sugarcane plantations. Between 2001 and 2008, the number of longan trees planted increased from 2300 to 11,800 with 65% at bearing age (National Agricultural Statistics Service, 2009). Year-round flowering of longan trees can be stimulated with potassium chlorate, facilitating a nearly continuous harvest season and orderly market supply (Nagao, 2009). Fruit are consumed locally and exported to U.S. mainland markets. Increased exports are needed to support the expansion in production. However, the fruit are hosts of the Mediterranean fruit fly (Ceratitis capitata) and oriental fruit fly (Bactrocera dorsalis) and undergo quarantine treatment at an X-ray irradiation facility on Hawaii Island before export via air shipment.
Consumer acceptance of this high value crop requires that fruit arrive at their final destination in excellent condition with minimal defects. However, pericarp darkening and postharvest diseases typically limit longan shelf life. Although skin browning does not impact edible aril quality, it reduces the visual appearance and commercial value of the fruit. Postharvest diseases of longan are primarily caused by fungal pathogens (Coates et al., 2003). In Hawaii, Phomopsis sp., Pestalotiopsis sp., Colletotrichum sp., and Lasmenia sp. have been isolated from infected fruit (Keith, 2005; Wall et al., 2010). Sulfur dioxide fumigation is used in Asian countries to prevent peel browning and control diseases, but SO2 use is prohibited in the United States (Jiang et al., 2002). Longan fruit quality may be retained through modified atmosphere packaging (MAP) in which high humidity, high CO2, and low O2 levels are created inside semipermeable films through fruit respiration and transpiration (Kader et al., 1989). An industry analysis identified the development of postharvest technology involving MAP as a research priority for Sapindaceae fruit (Nagao, 2009). Although packaging reduces water loss, the humid atmosphere can cause greater postharvest diseases especially at higher temperatures, which may occur during retail marketing. Knowledge of O2 and CO2 levels within a package is important because levels beyond those tolerated by a commodity can induce physiological disorders or anaerobic respiration and off-flavor development (Kader et al., 1989).
Optimum temperatures must be maintained during postharvest handling to maximize shelf life and fruit quality, especially when MAP is used. However, ideal storage temperatures have not been clearly established for longans, and reports range from 1 to 10 °C at 90% to 95% relative humidity (RH) (Drinnan, 2004; Jiang et al., 2002; Paull and Chen, 1987; Tian et al., 2002). Cultivars can differ in sensitivity to CI, modified atmospheres (MAs), and disease susceptibility, and the spectrum of fungi associated with diseased fruit can vary with storage temperature. Also, temperature fluctuations are common during shipping and retail handling and can impact the effectiveness of packaging. For these reasons, our research objectives were to determine the optimum storage temperature for ‘Biew Kiew’ longans, the most widely grown cultivar in Hawaii, and to evaluate different package types under controlled and variable temperature regimes to improve quality retention of exported longans.
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