Polyphenols from pigmented quinoa as potential modulators of maize starch digestion: Role of the starch-polyphenol inclusion and non-inclusion complexes

This study aimed to investigate the interaction modes between maize starch (MS) and quinoa polyphenols (QPs) under hydrothermal treatments and its influence on the multi-scale structure and digestive behaviors of MS through mechanistic analyses. Thermodynamic and microscopic results revealed that during starch gelatinization, the starch chains interacted with QP polyphenols to form new aggregates with retarded gelatinization. The X-ray diffraction and 13C nuclear magnetic resonance spectroscopy further confirmed the presence of both V-type inclusion complexes and non-inclusion complexes in QP-complexed MS. Through multiple spectroscopic approaches, it was demonstrated that complexation with QPs promoted the formation of local helical and short-range ordered structures and crystallization in MS and led to resistance of the starch chains to digestive enzymes. As a consequence, the MS–QP complexes showed substantially reduced digestion rates with increases in the contents of resistant starch and slowly digestible starch, as well as lower values of the predicted glycemic index. Compared to white quinoa polyphenols, polyphenols from red and black quinoa displayed a greater efficiency in modulating the starch structure and digestive properties. This study provides a valuable basis for the application of pigmented quinoa polyphenols as functional ingredients in starchy foods with desired glycemic response.