THE ROLE OF ORGANIC ACIDS AND NUTRIENT ELEMENTS IN RELATION TO BITTER PIT IN GOLDEN DELICIOUS APPLES
Bitter pit tissue has a higher concentration of calcium, potassium and magnesium than sound tissue as well as higher concentrations of oxalic and citric acid but a lower concentration of malic and succinic acid. In bitter pit tissue most of the calcium occurs in a water-insoluble form and thus is extractable with acetic and hydrochloric acid. Infiltration of apple tissue with oxalic and citric acid resulted in the disappearance of the middle lamellae similar to that found in bitter pit tissue. From these results an alternative mechanism for bitter pit induction and prevention is offered. It appears that localized excessive concentrations of oxalic and citric acid can induce bitter pit, as a result of their dissolving effect on the middle lamellae of cell walls. The suggested role of calcium is to eliminate the destructive effects of these acids by converting them to insoluble salts.
Steenkamp, J., Terblanche, J.H. and de Villiers, O.T. (1983). THE ROLE OF ORGANIC ACIDS AND NUTRIENT ELEMENTS IN RELATION TO BITTER PIT IN GOLDEN DELICIOUS APPLES. Acta Hortic. 138, 35-42