Relations between changes in starch molecular fine structure and in thermal properties during rice grain storage

The eating and cooking quality (ECQ) of stored rice grains is significantly affected by ageing, but the molecular mechanisms for this are not well understood. In the present study, changes of starch hierarchical structures and thermal properties of starch were investigated for rices with up to 12 months storage. For the first time, it was seen that storage resulted in molecular degradation of starch. This mainly involved shorter amylose chains and around (1 -> 6)-alpha glycosidic branching points of amylopectin, which altered the crystalline structure. This resulted in lower gelatinization temperatures and enthalpy but higher crystalline heterogeneity. The ageing effect was varietally-dependent. The information obtained from this study offers improved molecular-level understanding of the effects of ageing process on rice cooking and eating qualities.