Glycosidase activities in grapefruit flavedo, albedo and juice vesicles during maturation and senescence

Glycosidases were extracted from grapefruit ( Citrus paradisi Macf. cv. Ruby Red) flavedo, albedo, and juice vesicles harvested at five periods throughout the season. Flavedo β‐galactosidase activity was high at the September harvest and then significantly declined by November. Thereafter, no further changes occurred in β‐galactosidase activity. Flavedo α‐galactosidase activity was low and unchanged throughout the study. α‐Mannosidase, initially low in flavedo, steadily increased with advanced maturity. Trends in glycosidase activities of albedo were similar but attenuated. Juice vesicle β‐galactosidase did not change through the study period, whereas α‐galactosidase activity decreased 70% after the initial harvest period. α‐Mannosidase was initially high and then decreased to 50% of the original activity. A second peak of activity was measured in March, followed by a second decline. Extractability differences of the glycosidases suggest differences in compartmentation and function. Two isozymes of α‐mannosidase were separated in flavedo and one in juice vesicles, and characteristics were determined at an early and late harvest period. The results suggest that changes in the three glycosidases could be used to further define maturity and senescence in grapefruit.