Rice starches. II. Structural aspects provide insight into swelling and pasting properties

Abstract

The influence of starch structure (absolute (AAM), free (FAM), lipid complexed (LAM) amylose contents and amylopectin chain length distribution) on swelling behaviour (swelling power (SP), close packing concentration (C∗), total starch solubility (S) and amylose leaching (AML) in a temperature range between 55 and 125 °C) and pasting properties (6, 8 and 10% dry matter starch) of five waxy and 10 normal (low (three), intermediate (four) and high (three) peak gelatinisation temperature) rice starches was investigated. At temperatures between 55 and 85 °C, waxy starches had higher SP than normal starches. In this temperature range, however, SP and C∗ of the normal starches were independent of AAM and FAM. On the contrary, at temperatures between 95 and 125 °C, SP and C∗ of all starches decreased and increased with AAM and FAM contents, respectively. For the normal starches, SP decreased and C∗ increased with LAM contents at 65 °C. For all starches, relative amounts of short amylopectin chains with degrees of polymerisation (DP) 6–9 led to increased SP and decreased C∗ at 55 and 65 °C. Opposite results were observed for relative amounts of longer amylopectin chains with DP 12–22. AAM and FAM contents decreased with starting gel point temperatures (6, 8 and 10% dry matter starch) of normal intermediate and high peak gelatinisation temperature starches. Peak and breakdown viscosities (6% dry matter starch) decreased, whereas setback and final viscosities (10% dry matter starch) increased with AAM and FAM contents of all investigated starches. Chains of DP 6–9 and 12–22, respectively, decreased and increased starting gel point temperatures. No significant correlations between amylopectin chain length distribution and peak, breakdown, setback and final viscosities were observed.