In vitro digestibility of rice starch granules modified by β-amylase, transglucosidase and pullulanase.

It is highly desirable to lower the glycemic index of rice starch-based foods. Herein, rice starch granules were treated sequentially with β-amylase (BA), transglucosidase (TG) and pullulanase (PUL). The results indicated that compared with native rice starch and PUL-modified starch, degree of crystallinity, gelatinization temperature and enthalpy of BA/TG/PUL-modified starches increased remarkably. Moreover, the functionality of BA/TG/PUL-treated starch depended enormously on TG treatment time. BA/TG/PUL-modified starch possessed the highest relative crystallinity, gelatinization temperatures and gelatinization enthalpy and the content of resistant starch at TG treatment time of 20 h and the resistant crystals were formed largely from linear chains with DP 9-11. Whether before cooking or after cooking, BA/TG/PUL-modified starches had strong resistance to enzyme hydrolysis and had lower glycemic index. This outcome may offer a novel sight for the exploitation of starch-based functional foods with low glycemic index.