Enzymes of Sugar and Acid Metabolism in Stored ‘Valencia’ Oranges

Abstract

Abstract The activities of key enzymes of sugar and acid metabolism were measured in desalted protein extracts from ‘Valencia’ oranges [ Citrus sinensis (L.) Osb.] at 0, 3, 6, and 9 weeks of storage at 15C to investigate the relationship between the activities of gluconeogenic and glycolitic enzymes with postharvest changes in sugars and organic acids. Fructose-1,6-bisphosphatase (regulatory enzyme of the gluconeogenic pathway) activity was present throughout storage. Activities of the enzymes of acid metabolism (malic enzyme, isocitrate dehydrogenase/aconitase, and alcohol dehydrogenase) either increased during the first 3 weeks (malic enzyme) or remained constant during storage. Activity of enzymes involved in sugar catabolism (hexokinase, sucrose synthase, UDPG pyrophosphorylase, and PPi-dependent phosphofructokinase) increased during storage. These enzymes are necessary for organic acid use and for the subsequent oxidization of sugars in harvested sweet oranges.