CELL-WALL CHANGES AND PARTIAL PREVENTION OF FRUIT SOFTENING IN PRESTORAGE HEAT-TREATED ANNA APPLES

Prestorage heat treatment (38 degrees C for 4 days) retarded the softe ning of 'Anna' apple fruits during 0 degrees C storage. Fruit softenin g of unheated apples during storage was accompanied by changes in pect ic substances: a decrease in uronic acid content in the carbonate-solu ble fraction and an increase in the water-soluble fraction. Heat treat ment partially inhibited the degradation of uronic acids in the cell w all. The degree of pectin methylation in both heated and nonheated fru it decreased during storage. In heat treated apple fruit the content o f galactose and arabinose in the cell wall decreased during storage; i n non-heated fruit only galactose decreased. We suggest that the inhib ition of solubilisation of the carbonate soluble pectin fraction is on e of the main factors contributing to the firmness retention caused by heat treatment. The loss of both arabinose and galactose in heat trea ted fruits may also play an as yet undefined role in the effect of hea t treatment on fruit softening.