High hydrostatic pressure modulates the digestive properties of rice starch-gallic acid composites by boosting non-inclusion complexation

Influencing the starch postprandial glycemia via interventions that are sourced from natural plant materials has gained attention recently. Amylose present in starch is reported to form complexes with small ligands such as gallic acid (GA) through a conformational change that are digested slowly and contribute to the formation of resistant starch. In this study, the molecular interactions, multi-scale structure and in vitro digestion properties of normal neat rice starch and rice starch-GA composites (2, 5 % w/v) obtained either by high hydrostatic pressure (HHP) or thermal (T) treatment were compared. The multi-scale structure changes experienced by the rice starch gels (neat and composite) during simulated oro-gastrointestinal (OGIT) digestion were also characterised. Overall, formation of the V₇ type inclusion complex was demonstrated in the composite gels processed by HHP and T, although the main molecular interactions found in the composites were non-inclusion complexes. Sample A-GA-5-HHP formed gels with a unique microstructure, whilst also displaying a significant increase of the resistant starch fraction (∼13 %) and a large decrease of the rapidly digestible starch fraction than A-GA-5-T (p < 0.05). The lower digestibility in A-GA-5-HHP was attributed to increased molecular interactions between amylose and GA, as suggested by the greater intensity peak at 3520 cm^-1 in the FTIR, and the downfield chemical shifts (0.12 ppm) in the ¹³C NMR spectra. Our findings indicate that HHP gelatinisation of starch-GA composites represents a promising approach for the design of novel starch-based systems with distinct microstructure and digestion characteristics.