Covalent conjugates of anthocyanins to soy protein: Unravelling their structure features and in vitro gastrointestinal digestion fate

Seeking for healthier dietary foods without compromising their quality has become the first choice for consumers. Various components in foods are able to interact with each other and form conjugates to improve their functionality and nutritional value. The present study investigated on the formation and structural properties of covalently linked conjugates using soy protein isolate (SPI) and black rice anthocyanins at different ratios. The in vitro digestion fate of the conjugates under simulated gastrointestinal conditions was also evaluated. Fourier transform infrared spectroscopy analysis indicated that the secondary structures of SPI was changed upon conjugation with anthocyanins as there was a decrease in alpha-helix and beta-sheet content. Three-dimensional fluorescence also revealed that the tertiary structure of SPI was less compact after conjugation with anthocyanins as a result of the unfolding of polypeptide chains. The conjugates were shown to have higher degree of hydrolysis than SPI. However, transepithelial transport of peptides across Caco-2 cell monolayer was decreased in SPI after conjugation with anthocyanins. The results of this study suggest that incorporation of anthocyanins in SPI is a way to reconcile consumer demand for healthier foods with better quality and functionality.