Relations between chain-length distribution, molecular size, and amylose content of rice starches

Starch molecular structure, in terms of chain-length distribution (CLD) and molecular size, are important structural features regarding to “(starch) structure-property” relations for starch-based foods. In this study, amylopectin CLDs from fluorophore-assisted carbohydrate electrophoresis (FACE) are parameterized by a biosynthesis-based model, amylose CLDs and molecular sizes of amylose and amylopectin are measured by size-exclusion chromatography (SEC), and statistically meaningful relationships are established between starch CLDs, starch molecular size, and amylose content using rice starches with a wide range of amylose content. This shows that amylopectin molecular size is increased by increasing the proportion of short amylopectin chains with degree of polymerization (DP) 6-32 and decreasing the percentage of long amylopectin chains with DP 63-100. On the other hand, molecular sizes of both branched amylopectin and amylose molecules are negatively correlated with amylose content, suggesting that high-amylose rice tends to have smaller amylopectin and amylose molecular sizes. These relations are rationalized in terms of chain-length effects on the production of branched amylopectin and amylose molecules between different rice cultivars, which could provide new insights regarding to starch “structure-property” relations.