Preparation and characterization of genipin cross-linked and lysozyme incorporated antimicrobial sodium caseinate edible films

Sodium caseinate (NaCas) possesses good film forming capacity, but mechanical strength of NaCas films is declined by hydrophilic residues in NaCas molecules. Genipin (GP), a low-toxicity natural cross-linking agent, was used at the level at 1 mg/g NaCas to improve the mechnical properties and lysozyme (LYS) was used at the levels of 42, 84 and 126 mg/g NaCas to confer antimicrobial activity of NaCas films. While films without GP and LYS were colorless, light blueness was observed for all types of NaCas films containing GP. The whiteness index and transparency of films decreased as LYS amount increased. The moisture content of films was not significanly affected by the additon of GP and LYS, but the water vapor permeability slightly increased as the amount of LYS increased. Compared with films without GP, significanly higher tensile strength and Young's modulus and significantly lower break elongation were detected in NaCas films containing GP. The cross-linking reaction between NaCas and GP was confirmed by FTIR-ATR analysis. Incorporation of LYS into NaCas films exerted antimicobial activities against Staphylococcus aureus and Eschericha coli. In conclusion, a novel type of active edible food packaging film with antimicrobial activity was developed by cross-linked with GP and incoporated with LYS.