Characterization of fish-skin gelatin gels and films containing the antomicrobial enzyme lysozyme

Authors: Bower, Cynthia; Avena-Bustillos, Roberto; Olsen, Carl; McHugh, Tara; Bechtel, Peter

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2006
Publication Date: 7/20/2006
Citation: Bower, C.K., Avena Bustillos, R.D., Olsen, C.W., Mc Hugh, T.H., Bechtel, P.J. 2006. Characterization of fish skin gelatin gels and films containing the antimicrobial enzyme lysozyme. Journal of Food Science. 71(5):141-145

Interpretive Summary: Fish skins are composed of collagen and can be processed into gelatin for food and pharmaceutical use. Gelatin is traditionally produced from the collagen of cattle and pig skins, however this creates problems for people with kosher and halal dietary restrictions. Fish-skin gelatins not only comply with these dietary practices, but offer unique functional properties as well. For example, fish-skin gelatins have lower gelling temperatures and higher viscosities than their mammalian-derived counterparts. As more applications are found for fish-skin gelatin, safety issues may become a concern since bacterial contamination of mammalian gelatin is a well-documented problem. Lysozyme is a natural enzyme that can kill certain varieties of bacteria. The purpose of this study was to characterize the effect on strength and barrier properties of lysozyme-enhanced fish-skin gelatin gels and films, and to evaluate their efficacy as antimicrobial barriers to contamination. The results suggest that fish-skin gelatin gels and films, when formulated with lysozyme, may provide a functional barrier capable of increasing the shelf-life of food products.

Technical Abstract: Fish skins are rich in collagen and can be used to produce food-grade gelatin. Films cast from fish-skin gelatins are stable at room temperature and can act as a barrier when applied to foods. Lysozyme is a food-safe, antimicrobial enzyme that can also produce gels and films. When cold-water, fish-skin gelatin is enhanced with lysozyme, the resulting film has antimicrobial properties. The objective of this study was to characterize the effect on strength and barrier properties of lysozyme-enhanced fish-skin gelatin gels and films, and evaluate their activity against potential spoilage bacteria. Solutions containing 6.67% fish-skin gelatin were formulated to contain varying levels of hen egg white lysozyme. Gels were evaluated for strength, clarity, and viscoelastic properties. Films were evaluated for water activity, water vapor permeability and antimicrobial barrier capabilities. Fish-skin gels containing 0.1% and 0.01% lysozyme had pH (4.8) and gelling-temperatures (2.1°C) similar to lysozyme-free fish-skin gelatin controls. However, gel strength decreased (up to 20%). Turbidities of gels, with or without lysozyme, were comparable at all concentrations. Films cast with gelatin containing lysozyme demonstrated similar water vapor permeabilities, and water activities. Lysozyme was still detectable in most fish gelatin films. More antimicrobial activity was retained in films cast with higher lysozyme concentrations and in films where lysozyme was added after the gelatin had been initially heated. These results suggest that fish-skin gelatin gels and films, when formulated with lysozyme, may provide a unique, functional barrier to increase the shelf-life of food products.