Removal of starch granule-associated proteins promotes α-amylase hydrolysis of rice starch granule.

Starch granule-surface proteins (SGSPs) and granule-channel proteins (SGCPs) are granule-associated proteins (SGAPs), which have been found to be distributed on the surface and channels of starch granules, respectively. To investigate the impacts of SGAPs on α-amylase hydrolysis of starch, SGCPs or SGAPs of waxy, low and high amylose rice starches were removed. Removal of SGAPs or SGCPs greatly increased hydrolysis rate of rice starches. Meanwhile, these granules incurred a greater number and size of pores on their surfaces during hydrolysis. Compared to low and high amylose starches, waxy starch before and after removing SGAPs exhibited a higher hydrolysis rate. Rice starch hydrolysis began with enlargement of cavity and channels both horizontally and vertically. XRD analysis revealed that removal of SGAPs decreased relative crystallinity (RC) of starch and advanced changes in RC during hydrolysis process. This study provides new information about the role of SGAPs in the mechanisms of α-amylase hydrolysis.