Effect of porous waxy rice starch addition on acid milk gels: Structural and physicochemical functionality

Abstract

Waxy rice starch granules were digested by amyloglucosidase at 50 °C for up to 24 h. Granular and lamellar structures of the digested starch granules were studied using particle sizing, scanning electron microscopy (SEM), ultra-small angle neutron scattering (USANS), and small-angle X-ray scattering (SAXS). The appearance of spherical pores on the starch granule surface upon enzymatic digestion is identified by SEM. USANS was able to monitor changes in the pore polydispersity as digestion progressed. The size of the digested starch granules decreased with digestion time up to 8 h owing to enzymatic degradation. Excessive digestion (15 h and 24 h) resulted in a slight increase in apparent starch granule diameter, suggesting that the particles might be swollen or aggregated. Thermal (50 °C) and enzymatic treatments of the starch granules induced a destruction of the starch internal lamellar structures, with enzymatic digestion showing a more prominent effect. Incorporation of the digested starch granules into acid milk gels in a pasted form resulted in a decrease in elasticity, while their incorporation in a granular form resulted in a marked (nearly 3-fold) increase in the elasticity of the acid milk gels.