Modulating the in vitro digestibility and predicted glycemic index of rice starch gels by complexation with gallic acid

The starch digestibility strongly depends on the food composition and microstructure formed during food processing. To control rice starch digestion and glycemic response, rice starch was complexed with a dietary polyphenol. The interaction between starch and gallic acid (GA) and its influence on the in vitro digestibility of rice starch gel were investigated, which was correlated to the variation in GA fluorescence and the changes in starch pasting and gel properties. It was found that GA influenced the starch molecular rearrangement and aggregation and subsequently the multi-scale structures of rice starch gel. ATR-FTIR and SAXS results revealed that GA not only acted as a molecular chaperone to assist starch reassembly and to form starch ordered structures at a lower amount (4.54 and 11.24 mg/g starch), but also broke starch hydrogen bonding networks and reduced the ordered multi-scale structures of starch gel at a higher level (13.21 mg/g starch). After GA complexation, the resistant starch content in starch gel increased from 15.52% to 45.93% and thus decreased the predicted glycemic index (pGI). The synergistic effects of the reassembled ordered structures and the GA inhibitory activity against enzymes should be responsible for its nutritional changes. Thus, the digestibility and pGI of starch gel can be modulated through starch reassembly chaperoned with GA molecules.