Spatial distributions and structural effects of endogenous and exogenous α-glucosidase enzymes in rice grains during cooking

Endogenous and exogenous enzymes influence the sensory properties of cooked rice by acting on starch during gelatinization. This study elucidated the distinct spatial distributions of endogenous α-glucosidase (E-AG) and an exogenous version derived from Aspergillus niger (A-AG) during cooking. The E-AG, A-AG, and water distributions in rice grains were visualized. E-AG was distributed throughout the raw grain, whereas A-AG was localized around starch granules, amyloplasts, and cell walls, penetrating the grain and existing along cell walls during soaking. With A-AG, the cooking time was prolonged by approximately 1 min, and the temperature rise from 85 to 100 °C became more gradual. This may result from enzyme-added rice's enhanced starch hydrolysis and gelatinization, which increases endothermic reactions. The modified outer area obtained at 85-100 °C reached 58 ± 7% with A-AG and 52 ± 5% without. Moreover, the enzyme's preservation effect appears to be related to its localization.