The effect of heat treatment on apple epicuticular wax and calcium uptake

Golden Delicious apples (Malus domestica Borkh) were heated for 4 days at 38 degrees C and then dipped in 2% CaCl2, or dipped in the solution without prior heating. Scanning electron micrographs of the fruit wax layer after three days of 0 degrees C storage showed that the heated apples had areas of amorphous wax and fewer surface cracks than unheated apples. There was less wax on the surface of heated than on unheated apples. Electron density scan of apple wax showed more calcium in outer than inner wax area of undipped but heated apples, while the opposite obtained in unheated apples. Dips in calcium raised the wax calcium level of the unheated apples more than the heated ones. Plasma emission spectrometry of calcium in apple peel and flesh after 5 months storage at 0 degrees C showed greater penetration of calcium from the dips into unheated apples, compared to heated apples. It is suggested that during the heat treatment the wax softens and fills in cracks while water loss pulls calcium towards the fruit surface. This continuous wax layer on heated fruit decreases the ability of external calcium to move into the apple.