Removal of starch granule-associated proteins alters the physicochemical properties of diverse small granule starches

Abstract

The properties of four small-granule (oat, quinoa, amaranth and rice) starches before and after removal of starch granule-associated proteins (SGAPs), particularly surface-proteins and channel-proteins, were investigated and compared with two large-granule (waxy and normal maize) starches. The hypothesis, which was confirmed by results, was that the small-granule starches would be more susceptible to water and heat than the large-granule starches after removal of SGAPs on surfaces and in channels using protease. Surface-proteins of some granules in oat and rice starch presented as a film and channel-proteins were observed in oat, quinoa and rice starches. Compared to large-granule starches, removing SGAPs led to a greater reduction in gelatinization temperature for small granule starches. Meanwhile the reduced extent of rigidity of swollen small-granules during shearing was greater after removing SGAPs, corresponding to the reduced peak, breakdown and final viscosities. Furthermore, the removal of SGAPs for small-granule starch pastes weakened pseudoplasticity and shear-thinning behaviour. Removing SGAPs contributed to amylose leaching, accelerated the recrystallization and rearrangement of starch molecules, and facilitated retrogradation, thereby leading to a stronger gel network.