Pre- and postharvest calcium treatment of apple fruit and its effect on quality

Calcium is thought to be the most important mineral element determining fruit quality. It seems to be especially important in apples where it has been shown to reduce metabolic disorders. Calcium in adequate amounts helps to maintain apple fruit firmness and decreases the incidence of physiological disorders such as water core, bitter pit and internal breakdown. Postharvest decay may also be reduced by increasing the calcium content of apple fruit. The major problem is getting enough calcium into the fruit to have the desired effects. Soil treatments with calcium to increase fruit calcium concentration have often met with very little success. The direct application of calcium to the fruit is the most effective method for increasing fruit calcium content. This can be accomplished by preharvest sprays or postharvest dips or vacuum or pressure infiltration. Although calcium sprayed on apples on the tree can increase calcium content of the fruit, direct postharvest treatment of the fruit in solutions of calcium chloride can be even more effective. Pressure infiltration with solutions of calcium chloride can increase the calcium concentrations of apple fruit more effectively than vacuum infiltration which is more effective than dipping. Both pre- and postharvest calcium treatment methods have inherent problems. Inadequate calcium uptake is a problem in some cases in that not enough calcium is taken into the fruit to have a positive effect. In other cases, excessive calcium is taken into the fruit and injury results. Developing a commercially acceptable method of successfully increasing calcium concentration in fruit is a continuing challenge. In the meantime, orchard management to optimize fruit calcium uptake in the preharvest environment combined with supplemental postharvest application is the best strategy to prevent losses due to low fruit calcium.