Softening of several fruits and vegetables at low humidity with respect to their endogenous ethylene concentrations

Induction of softening in banana, cucumber, carrot and Japanese radish at low relative humidity (55% RH) was investigated with respect to their endogenous ethylene production. In banana, exogenous ethylene pretreatment rapidly hastened yellowing of the peel and softening of the flesh at both high and low RH. However, pretreatment with diazocyclopentadiene (DACP), and inhibitor of ethylene action, inhibited yellowing but did not prevent softening at high and low RH. In cucumber, carrot, and Japanese radish, softening of the firmness progressed at low RH even though endogenous ethylene activity was inhibited by DACP pretreatment. In cucumber, the flesh softened rapidly at low RH which was positively correlated to the increase in water soluble pectin and a decrease in sodium hexametaphosphate soluble pectin. These result may indicate that induction of softening in several types of fruits and vegetables proceeds independent of endogenous ethylene concentration, and that the degradation of cell wall polysaccharides is induced directly by water deficit stress.