Pectase in Doyenné Boussoch pears and changes in the quantity of the enzyme during development

The presence of pectase in Doyenne Boussoch pears was demonstrated by gel tests and the activity of the isolated enzyme was estimated titrimetrically. By measuring the rate of increase in viscosity of mixtures of pectin solutions and pear extracts, changes in the pectase content of the fruit during the development were investigated. The activity of the enzyme was found to be high in the young fruit, then to start falling off rapidly at about the middle of July and to straighten out to a low level some two weeks before the commercial picking time. Possible changes in the Ca content of the extracts used in the experiments were shown not to be responsible for the results obtained. The fact that the pectase content of the fruit does not decrease after picking as it does when left on the tree suggests an explanation for some of the difficulties encountered with the ripening of pears after cold storage.