Enzymatic synthesis of sodium caseinate-EGCG-carboxymethyl chitosan ternary film: Structure, physical properties, antioxidant and antibacterial properties

Proteins and polysaccharides have been frequently used in recent years to prepare environment-friendly packaging materials. However, films based on proteins or polysaccharides alone often have poor performance as packaging, so they need to be combined to improve properties. In this work, we applied enzyme technology to prepare sodium caseinate (SC)-carboxymethyl chitosan (CMC) films, incorporating epigallocatechin gallate (EGCG) as bridging molecules and antibacterial agents. SC-EGCG-CMC ternary conjugate was firstly synthesized by tyrosinase (Tyr), and the composite films were then prepared with the aid of glycerol. Under tyrosinase catalytic conditions, EGCG could cross-link with SC and CMC covalently. The effects of different concentrations of EGCG and tyrosinase on mechanical properties, water vapor permeability, antibacterial properties and free radical scavenging ability were studied. The crosslinking degree and mechanical properties were improved with the increase of EGCG and tyrosinase content. The film showed good antibacterial activity against Gram-positive bacteria. In addition, the antibacterial activity and free radical scavenging ability increased with the increase of EGCG concentration. This work provides an efficient enzymatic method to prepare films with good strength and antibacterial properties, which can be used to improve the storage quality of foods.