Modified sodium caseinate films as releasing carriers of lysozyme

Films made of sodium caseinate containing lysozyme where modified by chemical or biochemical crosslinkers to achieve a controlled release of the antimicrobial lysozyme. Kinetic studies in buffered solutions at pH 3.02–5.80 were undertaken. Both the pH and the use of crosslinkers had a strong effect on the protein network, and consequently, a significant influence on the releasing of lysozyme activity. Sodium caseinate (NaCas) films became insoluble networks at pHs close to the isoelectric point of caseinate (pH 4.6), therefore decelerating remarkably the diffusion of lysozyme without the addition of crosslinkers. Additionally a slow release of lysozyme was achieved after mixing with glyoxal, achieving a modulation in the antimicrobial activity against Micrococcus lysodeikticus and Staphylococcus aureus. Other crosslinkers, as calcium chloride or transglutaminase, almost blocked enzyme release and were not found adequate to achieve enough antimicrobial activity. Results showed that active caseinate films modified by pH and glyoxal efficiently retarded the release of lysozyme, being a promising way to extend antimicrobial effects during food storage and to enhance food safety.