ABSTRACT
Byproduct utilization is an important consideration in the development of sustainable processes. Whey protein isolate (WPI), a byproduct of the cheese industry, and gelatin, a byproduct of the leather industry, were reacted individually and in blends with microbial transglutaminase (mTGase) at pH 7.5 and 45 degrees C. When a WPI (10% w/w) solution was treated with mTGase (10 U/g) under reducing conditions, the viscosity increased four-fold and the storage modulus (G') from 0 to 300 Pa over 20 h. Similar treatment of dilute gelatin solutions (0.5-3%) had little effect. Addition of gelatin to 10% WPI caused a synergistic increase in both viscosity and G', with the formation of gels at concentrations greater than 1.5% added gelatin. These results suggest that new biopolymers, with improved functionality, could be developed by mTGase treatment of protein blends containing small amounts of gelatin with the less expensive whey protein.
Subject(s)
Bacteria/enzymology , Biopolymers/chemistry , Biotechnology/methods , Enzymes, Immobilized/chemistry , Milk Proteins/chemistry , Polymers/chemistry , Transglutaminases/metabolism , Adsorption , Cross-Linking Reagents , Dithiothreitol/chemistry , Gelatin/chemistry , Hydrogen-Ion Concentration , Milk Proteins/metabolism , Rheology , Temperature , Whey ProteinsABSTRACT
We compared the ability of two enzymes to catalyze the formation of gels from solutions of gelatin and chitosan. A microbial transglutaminase, currently under investigation for food applications, was observed to catalyze the formation of strong and permanent gels from gelatin solutions. Chitosan was not required for transglutaminase-catalyzed gel formation, although gel formation was faster, and the resulting gels were stronger if reactions were performed in the presence of this polysaccharide. Consistent with transglutaminase's ability to covalently crosslink proteins, we observed that the transglutaminase-catalyzed gelatin-chitosan gels lost the ability to undergo thermally reversible transitions (i.e. sol-gel transitions) characteristic of gelatin. Mushroom tyrosinase was also observed to catalyze gel formation for gelatin-chitosan blends. In contrast to transglutaminase, tyrosinase-catalyzed reactions did not lead to gel formation unless chitosan was present (i.e. chitosan is required for tyrosinase-catalyzed gel formation). Tyrosinase-catalyzed gelatin-chitosan gels were observed to be considerably weaker than transglutaminase-catalyzed gels. Tyrosinase-catalyzed gels were strengthened by cooling below gelatin's gel-point, which suggests that gelatin's ability to undergo a collagen-like coil-to-helix transition is unaffected by tyrosinase-catalyzed reactions. Further, tyrosinase-catalyzed gelatin-chitosan gels were transient as their strength (i.e. elastic modulus) peaked at about 5h after which the gels broke spontaneously over the course of 2 days. The strength of both transglutaminase-catalyzed and tyrosinase-catalyzed gels could be adjusted by altering the gelatin and chitosan compositions. Potential applications of these gels for in situ applications are discussed.
