The Activity of Starch-Hydrolysing Enzymes in Pears during Development and Cold-Storage

Some varieties of pears can no longer ripen after spending some time in coldstorage. An investigation has been made of the changes in the activity of a small number of enzymes in this fruit during growth and cold storage. The changes in the activity of a- and /9-amylase in three varieties of pears, gathered at different dates, were examined; these varieties differ considerably from the point of view of their post cold-storage ripening potentialities. During the pear’s development on the tree, the quantities of a- and /3-amylase increase to a certain extent. During cold-storage, the quantity of a-amylase continues to increase, reaching a value which is never achieved under natural conditions. The rise in a-amylase activity during cold storage proved to be entirely different for the three varieties of pears. There is a certain parallel between the rise in a-amylase activity and the possibility of ripening after cold storage, which was also found when a comparison was made of the first and second picking of the variety Comtesse de Paris. If the increase is not too excessive, ripening remains possible. If the rise in a-amylase activity is too great, at a rough estimate six to eight times the value at commercial picking-time, ripening is rendered impossible. In the ratio between the value for a-amylase activity in pears during cold-storage at a given moment and that about commercial picking time, we found an indication as to whether pears can still ripen or not. It is possible that a specific critical value exists for each variety.