Insights into chain-length distributions of amylopectin and amylose molecules on the gelatinization property of rice starches.

Starch gelatinization is an endothermic transition arising during rice cooking, which significantly influences rice eating and cooking quality (ECQ). The nature of starch (especially amylose) fine molecular structures that gives rise to this endotherm is however currently unclear. A modified Gomperz model was developed in this study to fit the differential scanning calorimetry (DSC) thermograms, resulting complementary information to the traditional DSC parameters. Correlation analysis between DSC parameters with starch chain-length distributions (CLDs) from 14 different rice starches showed for the first time that although amylose CLDs didn't affect starch gelatinization temperatures, the relative length of amylose medium chains was negatively correlated with the gelatinization temperature range. Furthermore, gelatinization onset and peak temperature as well as maximum gelatinization rate were negatively correlated with the relative length of amylopectin short chains, while the conclusion temperature were related to the relative length of amylopectin medium chains. Based on these results, a model for the arrays of amylopectin and amylose molecules within semi-crystalline lamellas of rice starch granules was proposed. These results will enable plant breeders to produce rice with desirable ECQs based on better understandings of the importance of starch fine molecular structures in determining starch gelatinization property.