Heat Treatment Affects Epicuticular Wax Structure and Postharvest Calcium Uptake in `Golden Delicious' Apples

Abstract

`Golden Delicious' apples ( Malus domestica Borkh) were pressure-infiltrated at harvest with a 4% CaCl 2 solution either without prior heat treatment 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 surface cracks that formed an interconnected network on the fruit surface. The epicuticular wax of heat-treated fruit did not exhibit a similar network of deep cracks. This apparent obstruction or elimination of deep cracks may limit the CaCl 2 solutions from entering the fruit. The heated fruit contained significantly less Ca than the fruit that were pressure-infiltrated with CaCl 2 solutions but not heated. These results indicate that cracks on the fruit surface may be an important pathway for the penetration of CaCl 2 solutions.