PECTIN ESTERASE-ACTIVITY AND PECTIN METHYL ESTERIFICATION IN HEATED GOLDEN DELICIOUS APPLES

Pectin methylesterase activity and the degree of methyl esterification of cell wall pectins were measured in Golden Delicious apples after a 4 day heat treatment at 38 degrees and after subsequent storage at 0 degrees of heated and unheated apples. Enzyme activity increased similarly during storage in both heated and unheated apples, although heated fruit softened much less than unheated. During storage, the degree of esterification decreased in both heated and unheated apples in water- and CDTA-soluble pectin, but not in insoluble pectin. In a comparison of three methods of determining methyl groups, similar values were obtained-for degree of bulk esterification of apple cell walls, regardless of treatment. Results Presented do not confirm a role for pectin methylesterase or for de-esterification in apple fruit softening.