HEAT-TREATMENT AFFECTS EPICUTICULAR WAX STRUCTURE AND POSTHARVEST CALCIUM-UPTAKE IN GOLDEN DELICIOUS APPLES

'Golden Delicious' apples (Malus domestica Borkh) were pressure-infilt rated at harvest with a 4 % CaCl2 solution either without prior heat t reatment or following 4 days at 38C. Examination of the apple surfaces from both treatments by low-temperature scanning electron microscopy revealed that heat treatment changed the pattern of epicuticular wax. The epicuticular wax of nonheated fruit exhibited numerous deep surfac e cracks that formed an interconnected network on the fruit surface. T he epicuticular wax of heat-treated fruit did not exhibit a similar ne twork of deep cracks. This apparent obstruction or elimination of deep cracks may limit the CaCl2 solutions from entering the fruit The heat ed fruit contained significantly less Ca than the fruit that were pres sure-infiltrated with CaCl2 solutions but not heated. These results in dicate that cracks on the fruit surface may be an important pathway fo r the penetration of CaCl2 solutions.