Porous rice starch produced by combined ultrasound-assisted ice recrystallization and enzymatic hydrolysis

The effects of multicycle ultrasound-assisted ice recrystallization (US+IR) combined with amyloglucosidase (AMG) or maltogenic α-amylase (MA) catalyzed hydrolysis on structure were investigated. Scanning electron microscopy (SEM) showed that the US+IR produced shallow indentations and grooves on the exterior of granules while the combination US+IR and enzyme hydrolysis created additional pores on starch granules. MA displayed a higher number of pores than AMG. The highest values of specific surface area (SBET) and the total pore volume were obtained for US+IR→MA (1.96 m2 g-1 and 7.26 × 10-3 cm3 g-1, respectively). The US+IR treatment significantly decreased the relative crystallinity, amylose content and swelling capacity. Those parameters were further efficiently decreased following enzymatic hydrolysis. The combined treatments generated products with higher initial gelatinization temperature (Ti) compared to the corresponding controls. The US+IR increased the digestion rate constant (k-value) compared to native starch. However, the combined treatment, US+IR→AMG, significantly decreased the k-value from 2.97 × 10-3 to 2.50 × 10-3 min-1 compared to its control. Our study demonstrates that US+IR treatment in combination with enzyme hydrolysis is a useful method to produce specifically functionalized porous rice starch that can be used as e.g. absorbents and for further chemical modifications.