Enzyme modification of starch granules: in situ reaction of glucoamylase to give complete retention of d-glucose inside the granule

Starch granules have been modified in situ by using a reaction system in which glucoamylase reacts inside starch granules to give conversions of 10–50% d-glucose inside the granule. Waxy maize, maize, and amylomaize-7 starches were converted to the extent of 18.4, 15.0, and 9.4%, respectively, after reaction for 24 h and to 51.0, 33.8, and 24.4%, respectively, after reaction for 288 h. The reaction conditions, of solid granules with a relatively low amount of water and glucoamylase inside the granule, gave 100% retention of d-glucose inside the granule. The amount of d-glucose obtained inside the granule depends on the length of time of the reaction and the type of starch. The action of glucoamylase inside the granule can be terminated by heating at 110−120° C for 20 min. By stopping the reaction at selected periods of time, starch granules were obtained that contained 10–50% (w/w) d-glucose inside the granules.