Relation between the solubilization of pectin and the fate of organic acids during maturation of apples

The amount, degree of esterification and molecular weight of pectins in apples were investigated weekly during some months before and after harvest. Since molecular weight of pectin has been found constant during that period and the molecular weights of insoluble and soluble pectins in ripe fruits are nearly equal, there seems to be no shortening of chains of pectin molecules during the solubilization of a part of the pectins during ripening. The correlation between changes in solubility of pectin and in solubility of calcium, changes in the composition of the mixture of organic acids in the fruits, and some experimental evidence of a change of the pH of cell walls during that period, may be an indication that solubilization of pectin during ripening of fruits is caused by movement of calcium in the cell walls. Experiments on the relation between behaviour of calcium and solubility and swelling of pectin in cell walls and in artificial pectin films are discussed.