Modeling of in vitro digestogram by consecutive reaction kinetics model reveals the nature of starch digestive characteristics

Starch digestion involves enzymatic binding and consecutive catalysis steps, while their relative contribution to the overall digestion kinetics and relations to both starch chemical and physical structures are currently unknown. A consecutive reaction kinetics model (CRK) was developed in this study to modelling in vitro starch digestograms of 15 retrograded rice starches. Fine molecular structures, ordering of retrograded crystallites and physical forms of these retrograded starches were obtained from our published data. Results showed that starch digestograms can be satisfactorily deconvoluted by the CRK model into a combination of enzymatic binding and catalysis curves. More importantly, it for the first time showed that enzymatic binding is the rate-limiting step during the digestion process. Correlation analysis among CRK model-fitted parameters with starch structural parameters showed that starch digestive enzymes had a distinct binding affinity and catalytic activity towards different starch chemical and physical structures. These results help a better understanding of the starch digestion process and subsequently the design of functional foods with slower starch digestibility.