Rice starches. I. Structural aspects provide insight into crystallinity characteristics and gelatinisation behaviour of granular starch

Abstract

To gain an understanding of the contribution of structural aspects to the gelatinisation behaviour of rice starch, five waxy and 10 normal rice starches, isolated from 15 milled rice samples, were analysed for structural features [absolute (AAM), free (FAM) and lipid-complexed (LAM) amylose contents, amylopectin chain length distribution and relative crystallinity] and gelatinisation behaviour as evaluated by differential scanning calorimetry. In doing so, the normal rice starches were classified according to their peak gelatinisation temperatures (Tp) as low, intermediate and high Tp rice starches. Higher AAM and FAM contents went hand in hand with decreased onset (To), Tp and conclusion (Tc) gelatinisation temperatures and increased gelatinisation range (Tc−To) of normal intermediate and high Tp starches, whereas LAM contents increased with To, Tp and Tc and decreased with Tc−To of all investigated starches. For all starches, the relative amounts of amylopectin chains with degree of polymerisation (DP) 6–9 were negatively correlated with To, Tp and Tc and positively with Tc−To. On the contrary, chains of DP 12–22 increased gelatinisation temperatures and decreased Tc–To. Furthermore, To, Tp and Tc of the normal rice starches increased with relative crystallinity.