Dragon fruit is an exotic tropical fruit produced by epiphytic, night-blooming Hylocereus cacti of neotropical origin. Also known as pitaya, pitahaya, strawberry pear, and thang loy, the fruit are oblong–oval with bright red skin covered with green bracts or “scales,” accounting for the name dragon fruit (Morton, 1987; Paull, 2004). The flesh is sweet, delicate, white or red–purple, and contains numerous tiny black seeds. The fruit is nonclimacteric and has the best flavor when harvested at full red color (Nerd et al., 1999).
Dragon fruit is being grown commercially in Israel, Vietnam, Taiwan, Nicaragua, Australia, and the United States (Merten, 2003). Two species (H. undatus and H. polyrhizus) and their hybrids comprise most of the production. Dragon fruit is enjoyed as a fresh fruit or juice, but also is valued as a natural food colorant. The red peel of both species as well as the red–purple flesh of H. polyrhizus contain water-soluble betacyanin pigments similar to those found in red beets (Beta vulgaris) (Wybraniec and Mizrahi, 2002).
In Hawaii, dragon fruit is a new specialty fruit crop grown for local consumption but has potential to supply U.S. mainland markets. However, dragon fruit is a host for tephritid fruit flies and therefore subject to quarantine restrictions. Hot forced air treatments have been proposed for dragon fruit disinfestation with minimal reduction in quality (Hoa et al., 2006); however, irradiation generally is more efficient and less phytotoxic than heat treatments for tropical fruit (Follett and Sanxter, 2000, 2002, 2003). Irradiation may be the most widely tolerated of all the major phytosanitary treatments, especially at the low doses required for quarantine security against fruit flies and many other pests (Hallman, 2001). The USDA's Animal Plant Health Inspection Service (APHIS) allows export of dragon fruit from Hawaii after irradiation with a 400-Gy dose or after irradiation with a 150-Gy dose and inspection for mealybugs (Dysmicoccus neobrevipes, Maconellicoccus hirsutus, and Pseudococcus cryptus) (APHIS, 2008). The island of Hawaii has a commercial electron beam facility that is used for quarantine treatment of tropical fruits. Local growers are interested in exporting irradiated dragon fruit from Hawaii, but quality and sensory analyses are needed before markets can be developed and large shipments can be risked.
Dose uniformity ratios at the commercial electron beam facility in Hawaii (designed to treat fresh produce) are typically 1.5 to 2.0 (Follett et al., 2007). Therefore, commodities treated with a minimum absorbed dose of 400 Gy may receive maximum doses of 600 to 800 Gy irradiation, which may approach or exceed fruit tolerance limits. Dragon fruit injury must be absent or minimal before irradiation treatment can be used commercially. There are no published reports of dragon fruit radiotolerance limits. Therefore, the objectives of this study were to determine the quality of dragon fruit exposed to irradiation doses 800 Gy or less.
Animal and Plant Health Inspection Service (APHIS), U.S. Department of Agriculture 2008 Interstate movement of fruit from Hawaii. Final rule Fed. Regist. 73 24851 24856
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