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J. H. MOY, Dept. of Food Science and Human Nutrition, University of Hawaii, 1920 Edmondson Rd., Honolulu, HI 96822, W. Q. Peng, and L. Wong, Dept. of Agriculture, State of Hawaii, 1428 King St., Honolulu, HI 96815.

JUSTIFICATION: Irradiation is effective as a quarantine treatment of tropical fruits to prevent fruit flies from entering into non-infested areas. USDA requires Hawaii-grown fruits be treated with an approved treatment procedure before allowing fruits to be exported to the U.S. Continent. Approved vapor heat treatment requires several hrs, is commodity-specific, and sometimes caused undesirable texture changes. Treatment by irradiation, also allowed, is efficient and effective, but also requires knowing the tolerance of each fruit to radiation. With a minimum dose of 0.25 kGy, tropical fruits recently studied at the Hawaii Research Irradiator such as papaya, mango, litchi, and carambola have shown good tolerance to irradiation. Atemoya, a relatively new tropical fruit grown in Hawaii, sometimes exhibits darkening of the skin and pulp after irradiation. It is important to determine whether this problem can be minimized through some pretreatment procedures.

OBJECTIVES: Our objective is to find ways to improve the tolerance of atemoya to radiation in order to improve its marketability.

METHODS: Several pretreatments were applied to atemoya (cv. African Pride) including chemical dips (NaH₂PO₄, lactic acid, calcium chloride, or in combination), heat shock, and dose fractionation. Treated fruits were examined for pretreatment effectiveness.

RESULTS: Results show pretreatment with a 15% CaCl₂ solution dip at 40 deg C for one hr retained the skin and pulp color of those irradiated at 0.50 kGy for up to 2 wks. Dipping fruits in a 10% NaH₂PO₄ solution at 40 deg C for one hr was effective in minimizing darkening of fruits irradiated at 0.75 kGy. Fruits treated by dose fractionation also showed less darkening than those irradiated without pretreatment.

SIGNIFICANCE: Several pretreatments have demonstrated varying degrees of effectiveness in minimizing post-irradiation darkening of skin and pulp of atemoya. More work is needed to optimize various pretreatments and to understand the mechanism of darkening.