Study on the interaction mechanism of purple potato anthocyanins with casein and whey protein

To investigate the interaction mechanism of casein (CA) and whey protein (WP) with anthocyanins from purple potato flour (PPA), multiple spectroscopic techniques and molecular docking simulation were used. After extraction and purification, two non-acylated anthocyanins and three acylated anthocyanins were identified in purple potato flour using UPLC-Q/TOF-MS. The fluorescence quenching experiment found that PPA could effectively quench the intrinsic fluorescence of CA and WP by static quenching. CA had a stronger binding affinity toward PPA than WP did, with respective Ka values of 4.23 × 105 M−1 and 1.66 × 105 M−1 at 297 K. Structural analysis indicated that PPA bound CA and WP through hydrogen bonds and van der Waals forces, and the number of bound anthocyanin molecules (n) was approximately equal to 1. The ΔG values of PPA binding with CA and WP were −30.96 kJ mol−1 and -29.16 kJ mol−1, respectively, which suggested that the binding reaction was spontaneous. Moreover, the conformational structures of CA and WP were altered by PPA binding with a decrease in α-helix and β-turn contents and an increase in β-sheet and irregular coil contents. Molecular docking analyses showed that CA and WP had different binding sites with anthocyanins. This study is helpful to better understand the interaction mechanism of CA and WP with anthocyanins and provides guidance for their applications in the food industry.