Effects of collagen and casein with phenolic compounds interactions on protein in vitro digestion and antioxidation

Abstract The interaction between fish skin collagen (C), casein (CS) with tannic acid (T) or Gallic acid (G) and the effect of the addition of mixed polyphenols on protein properties were investigated. Polyphenols induced structural changes, affected digestion and antioxidant properties of the protein. The fluorescence results showed that the binding constants of the protein-polyphenol complexes were in the range from 104 to 107 L mol−1. Circular dichroism and Fourier transform infrared (FTIR) spectroscopy indicated that both single polyphenols and mixed polyphenols changed the protein secondary structure. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the polyphenols advanced the loose protein structure. After the gastrointestinal digestion, the proteolysis occurred in the small intestine, and the polyphenols reduced the degree of hydrolysis of the protein significantly and affected the antioxidant properties. This study can offer health guidance in the preparation of diets and beverages.