Complexation of thermally-denatured soybean protein isolate with anthocyanins and its effect on the protein structure and in vitro digestibility.

The complexation of anthocyanin-rich black rice extracts (ARBRE) with soybean protein isolate (SPI) heated at 0, 70, 85, and 100 °C and its effect on protein digestibility were studied. The structural changes of SPI during its interaction with ARBRE in all the samples were studied by Fourier transform infrared, circular dichroism, and fluorescence spectroscopy. The secondary structure changes of SPI in all the samples after complexation with ARBRE showed a significant increase in α-helix and a significant decrease in β-sheet contents. Results also showed that ARBRE quenched the SPI fluorescence (in both unheated and heated samples) via static quenching with a single binding site. The digestibility of unheated and heated SPI was improved upon complexing with ARBRE. The formation of the SPI-ARBRE complexes is beneficial for the application of soy protein-based products in foods by increasing their protein digestibility and nutritional quality.