Calcium and the firmness of kiwifruit

Abstract The effect of calcium (Ca) concentration on the firmness of kiwifruit during cool‐storage was investigated by (a) postharvest dipping of fruit in CaCl 2 , and (b) comparing endogenous Ca and firmness of fruit which differed in one of the following orchard or fruit variables: fruit size; crop load; position of the fruit on the vine; exposure to sunlight during growth; and irrigation treatments. Postharvest dipping of kiwifruit in 2,3,4, or 5% CaCl 2 reduced the rate of fruit softening early in storage, resulting in fruit which were firmer after storage than control fruit. However, severe pitting of the fruit skin developed during storage as a result of dipping in 5% CaCl 2 . Total endogenous Ca levels in kiwifruit from several orchard sources ranged from 1.7 to 2.7 mg/g dry weight, but were not correlated with fruit firmness during storage. Furthermore, lines of kiwifruit which became particularly soft during storage had Ca concentrations similar to or even higher than lines of fruit which had remained firmer. These results are discussed in relation to the prediction of fruit firmness during storage, and the potential of developing commercial postharvest treatments for maintaining firmness of kiwifruit.