The role of ?-glucosidase in the biosynthesis of 2,5-dimethyl-4-hydroxy-3(2H)-furanone in strawberry (Fragaria �ananassa cv. Elsanta)

Some flavour and colour compounds are present in cells as glucosides. Their hydrolysis to form volatile aglycones is catalysed by glucosidases. Strawberry β-glucosidase (β-glucoside glucohydrolase, EC 3.2.1.21) was characterized in crude extracts of strawberry fruits. Enzymatic activity was measured by visible spectrophotometry using p-nitrophenyl-β-D-glucopyranoside as substrate. Strawberry β-glucosidase had pH optimum at pH 4 and temperature optimum at 60 °C. The enzyme followed typical Michaelis kinetics with a Km of 18.5 mM. The Vmax value was 474 × 10 −6 (IU/ml) for p-nitrophenyl-β-D-glucoside (40 °C). β-Glucosidase activity was high in unripe green strawberries, increased slightly during ripening and then decreased below pre-ripening levels in the fully ripe fruit. The levels of 2,5-dimethyl-4-hydroxy-2H-furan-3-one (DMHF) and DMHF-glucoside both increased greatly during ripening. The results are discussed in terms of the role of strawberry glucosidase on flavour biogenesis.