Effects of different polyphenols on the structure and properties of sodium caseinate films mediated by tyrosinase

This study evaluated the effects of tyrosinase (Tyr) catalysis on the properties of composite films consisting of sodium caseinate (SC) and polyphenols. The effects of polyphenol type, including epigallocatechin-3-gallate (EGCG), gallic acid (GA) and tannic acid (TA), on the basic properties of the composite films were explored. Analysis using sodium dodecyl sulfate polyacrylamide gel electrophoresis, fluorescence, infrared, and circular dichroism spectroscopies confirmed that a covalent interaction occurred between SC and the polyphenols after catalysis with tyrosinase. The molecular structure and physicochemical properties of SC were influenced by attachment of the polyphenols, which altered the protein's film-forming properties. Compared to non-covalent composite films, the porosity was lower, the mechanical strength was higher, and the water vapor permeability was higher for the covalent-composite films. The degree of cross-linking between SC and EGCG was greater than for the other polyphenols, which led to better mechanical and barrier properties in the films formed from SC-EGCG conjugates. This study shows that polyphenols can be used to improve the properties of edible films made from an important milk protein