LAUSR

BACKGROUND Starch-based foods (e.g. rice) usually contain multiple starch fractions with distinct digestion rate constants, while their nature is currently unknown. This study applied the recently developed consecutive reaction kinetics model to fit the in vitro digestion curves for starch fractions deconvoluted from the overall digestograms to differentiate their binding and catalysis rates to starch digestive enzymes. The fitting parameters were then correlated with starch molecular structures obtained from published data to understand starch structural features determining the binding and catalytic rate constants. RESULTS Binding and catalysis rates for the rapidly (RDF) and slowly digestible starch fraction (SDF) were controlled by distinct starch structural features. Typically, (1) the binding rate constant for RDF was negatively correlated with the amount of amylose short to intermediate chains, while positively correlated with the relative length of amylopectin intermediate chains; (2) catalysis rate constant for RDF was negatively correlated with the amount of amylose short to intermediate chains, relative length of amylose intermediate chains and amount of amylopectin long chains, while positively correlated with starch molecular size as well as relative length of amylopectin intermediate chains; (3) catalysis rate constant for SDF was negatively correlated with the amount of amylopectin long chains, while positively correlated with starch molecular size. CONCLUSION These results provide a better understanding of the nature of different starch digestible fractions and the development of foods such as rice with slow starch digestibility. This article is protected by copyright. All rights reserved.