Rice starches. III. Structural aspects provide insight in amylopectin retrogradation properties and gel texture

The long term amylopectin retrogradation behaviour of five waxy (low peak gelatinisation temperature (T(p))) and 10 normal (low (three), intermediate (four) and high (three) T(p))) rice starches was investigated by differential scanning calorimetry (DSC) rescan following gelatinisation in excess water (1:2 w/w starch/water). Textural attributes of rice starch gets (stored during 2 days or 2 weeks at 6 degreesC) were studied following gelatinisation (8% dry matter starch) in a Brabender visco-amylograph. Both amylopectin retrogradation and gel textural characteristics were related to absolute (AAM), free (FAM) and lipid-complexed (LAM) amylose contents and amylopectin chain length distributions. Upon storage at ambient temperature (2 and 4 weeks), retrograded amylopectin DSC conclusion temperatures were not related to AAM and FAM contents. Upon 4 weeks storage at 6 degreesC, however, retrograded amylopectin conclusion temperatures and enthalpies of the investigated normal intermediate and high Tp rice starches were negatively related to both AAM and FAM contents. LAM was positively correlated with retrograded amylopectin conclusion temperatures and enthalpies in the case of 4 weeks at ambient temperature and 6 degreesC, suggesting heterogeneous nucleation. Relative amounts of antylopectin chains with DP 6-9 and DP > 25 decreased amylopectin retrogradation conclusion temperatures and enthalpies, whereas opposite results were observed for chains of DP 12-22. Higher correlations were found with increasing storage temperatures and times. Firmness and force after relaxation increased and elasticity (2 days of storage at 6 degreesC) decreased with increasing AAM and FAM contents, whereas no correlations with LAM were observed. No significant correlations between amylopectin chain length distribution and gel texture were observed. (C) 2003 Elsevier Science Ltd. All rights reserved.