Chemometric analysis of cooked rice texture in relation to starch fine structure and leaching characteristics

Cluster, correlation, and multivariate regression analyses were used to rationalize the effects of grain composition, starch fine structure, and leaching characteristics on cooked rice texture (hardness and stickiness). The head rice grain composition of 23 U.S. long-grain cultivars was evaluated in terms of apparent amylose content, crude protein, and surface lipids. Starch samples were prepared by extraction with dilute alkali and amylopectin fine structure was characterized by high-performance anion-exchange chromatography with pulsed amperometric detection. Hardness and stickiness of head rice samples cooked in optimum water were measured with a texture analyzer. The amylose amylopectin ratio (AAR) of the material that leached out of the grains on cooking was evaluated by high-performance size-exclusion chromatography (HPSEC). Simple correlation and multivariate linear regression analyses pointed to AAR as the main indicator of cooked rice hardness and stickiness. Cluster analysis showed that the leached starch from soft-cooking, high-amylose cultivars (e.g., Jodon and L-202) generally had a higher proportion of amylopectin than amylose (AAR<1). In contrast, dry-cooking, high-amylose cultivars (e.g., Newrex and L-205) leached out starch with a higher proportion of amylose than amylopectin (AAR>1) during cooking. The amount of leached materials itself was also higher for the soft-cooking cultivars than the dry-cooking counterparts. Cultivar differences in leaching characteristics were attributed to variations in apparent amylose content, crude protein, and amylopectin chain-length distribution.