Relationship between alpha-glucosidase activity and physical and chemical properties of rice

To examine the relationship between alpha-glucosidase and the physical and chemical properties of rice quality for human consumption, we measured alpha-glucosidase and two other saccharification enzyme activities and physicochemical properties of twenty-four kinds of milled rice originally harvested in 1997. Koshihikari and Akitakomati (modern varieties) had higher alpha-glucosidase activity than Akamai (Tsushima, local red rice) and Sinriki (old variety). On the other hand, Akage (old variety) and Akamai (Tanegashima, local red rice) had higher alpha-amylase activity than Koshihikari. alpha-Glucosidase activity showed a negative correlation with starch-iodine blue value, total solid of residual liquid, expanded volume in cooking quality of milled rice (gamma= -0.542, gamma= -0.570, gamma= -0.460, respectively) and amylose content (gamma= -0.487). alpha-Glucosidase activity also showed a positive correlation with maximum viscosity and breakdown (gamma=0.557 and gamma=0.633, respectively) in pasting properties of milled rice flours employing a Rapid Visco Analyser. These results suggested that the same activity was indirectly associated with eating quality. From the principal component analysis (PCA) for all examined measurements, the first principal component represented amylose characteristics and the second principal component represented reducing sugar characteristics. The plot of PCA defined by these two factors indicated amylose characteristics, and also a chronological order of rice on the first principal component. Moreover, alpha-glucosidase had a higher factor loading (0.778) on the first principal component, which suggests that alpha-glucosidase may be related to some parts of amylopectin synthesis.