Molecular causes for the increased stickiness of cooked non-glutinous rice by enzymatic hydrolysis of the grain surface protein

Abstract

Non-glutinous rice has higher amylose content but less sticky texture than glutinous rice. In this study, by soaking two non-glutinous rice with protease solution, rice stickiness is significantly increased and equivalent to that of glutinous rice. By exploring starch leaching behavior during rice cooking, we find: (i) total solids and amylopectin amount in the leachate are significantly increased by raising the protease concentration during the soaking treatment; (ii) molecular size and chain-length distribution (CLD) of leached starch from these protease-treated rice (PTR) significantly differed from the corresponding native starch; (iii) strong correlations between rice stickiness, amylopectin amount and the proportion of short amylopectin chains with degree of polymerization (DP) <36 in the leachate are established. The possible molecular mechanism for the increased stickiness of treated non-glutinous rice is put forward to explain the above result. This study could broaden the applications of non-glutinous rice for rice industry.

Keywords: Chain-length distribution; Molecular size; Non-glutinous; Protease; Stickiness.