Enzymatic modification of hydrolysis products from collagen using a microbial transglutaminase. I. Physical properties

In previously reported research from this laboratory, gelatins, both commercial and experimental of varying gel strengths, were chemically modified using glutaraldehyde, glyoxal, and carbodiimide. These classical modifications effectively changed the physical and functional properties of gelatin; however, they have drawbacks in that the crosslinking agents are potentially toxic. Transglutaminase is an enzyme capable of forming inter- or intra-molecular cross-links in many proteins. The enzyme catalyzes an acyl transfer reaction between the gamma-carboxamide group of peptide-bound glutamine residues as acyl donors and primary amines as acceptors. When the epsilon-amino group of peptide-bound lysine acts as acyl acceptor, an epsilon-(gamma-glutamyl) lysine cross-link is formed. This enzyme, now isolated by fermentation, is commercially available, relatively inexpensive, and environmentally safe. We modified gelatins of varying quality with microbial transglutaminase. Gel strengths of low bloom gelatins improved with increasing enzyme concentrations, whereas the gel strengths of higher bloom gelatins either remained the same or decreased with increasing enzyme concentrations. All gelatins gave higher melting points with increasing amounts of enzyme, some even higher than 90degreesC. Viscosities, measured at 60degreesC and at or near room temperature, increased with increasing enzyme concentrations. The temperature of gelation, as described in the literature, increased not only with the quality of the gelatin but also with increasing enzyme concentrations. Potential applications for this enzyme in by-product utilization and possibly the leather-making process are numerous.