A POSTHARVEST HEAT-TREATMENT INHIBITS CELL-WALL DEGRADATION IN APPLESDURING STORAGE

Prestorage heating (38-degrees for four days) of apples (Malus domesti ca, cv Golden Delicious) leads to enhanced retention of fruit firmness during storage and poststorage ripening, but the mechanism of action is unknown. Softening of Golden Delicious fruits during storage at 0-d egrees was accompanied by an increase in H2O-, and CDTA (trans-1,2-dia minocyclohexane-N,N,N'N'-tetraacetic acid-soluble pectin), a decrease in uronic acid content in Na2CO3-Soluble pectin, and no change in the uronic acid present in the insoluble fraction of the cell wall. These changes did not occur in heated fruit during storage. During four days at 38-degrees, arabinose and galactose content of the cell wall decre ased with no accompanying decrease in uronic acids, while in unheated fruit there was a gradual loss of these three cell wall components dur ing the five months of storage. The decrease in arabinose during fruit heating was mostly from the pectic fractions, while galactose decreas ed in both pectic fractions and the insoluble residue. We suggest that loss of neutral sugar side chains during the heat treatment may lead to closer packing of the pectin strands and in turn hinder enzymatic c leavage during and after storage, resulting in firmer fruit.