Cell wall hydrolysing enzymes and fruit softening in apple as affected by controlled atmosphere storage conditions

The fruits of apples cv. 'Golden Delicious' were harvested at preclimacteric and climacteric stages of ripening and stored at 1°C for six months under conventional cold (Cold; 0.03% CO 2 and 21% O 2 ), controlled atmosphere (CA; 3% CO 2 and 3% O 2 ) and ultra low oxygen (ULO; 3% CO 2 and 1% O 2 ) conditions. Maximum retention of fruit flesh firmness was observed under ULO followed by CA and cold storage conditions. The activities of both isolated and cell wall bound preparations of polygalacturonase showed no correlation with fruit firmness. The activity of pectin methylesterase was not affected by various storage conditions. Cellulase activity could not be detected. The activity of β-D-galactosidase and the amount of soluble polyuronides in the flesh increased during storage and showed an inverse relation with fruit firmness under various storage conditions. Anion exchange chromatography on DEAE-Sephadex A-25 resin yielded only one peak of β-galactosidase activity. The above results were almost similar in preclimacteric and climacteric apples. The possible mechanism by which the storage conditions affect fruit firmness and cell wall metabolism has been discussed.