Maryann M. Taylor

Enzyme-catalyzed gel formation of gelatin and chitosan: potential for in situ applications.

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 transglutaminases 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 gelatins gel-point, which suggests that gelatins 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.

Processing of leather waste: pilot scale studies on chrome shavings. Isolation of potentially valuable protein products and chromium

Hides come to the tanner as a by-product of the meat industry. The tanning process, in turn, generates much greater quantities of by-products and wastes than leather. One ton of wet salted hides yields only 200 kg of leather but over 600 kg of solid waste, or by- product if a market can be found. In the United States, nearly 60,000 metric tons of chromium-containing solid waste, i.e. chrome shavings, are generated by the leather industry each year, and approximately ten times this amount is generated worldwide. Land application for the disposal of chromium-containing tannery and other leather wastes has been widely practiced during most of the twentieth century, but fewer landfill sites can be found every day and the cost of transportation and disposal increases. Historically, these materials were used in the production of fertilizer or composite boards, but while once the company producing and marketing fertilizer or boards would pay for the waste and its transportation, nowadays, the tanner has to pay for such things. Over several years, we have demonstrated that it is possible to isolate protein products (gelatin and collagen hydrolysate) from chrome shavings by using an alkaline protease under mild conditions. The objective of the present work was to perform pilot plant trials to isolate protein products from chrome shavings, treat and purify the remaining chrome cake and tan hides with the recovered chromium. Because of the high nitrogen content, the isolated collagen hydrolysate has potential use as a fertilizer and in animal feed additives. The gelatin has potential use in cosmetics, adhesives, printing, photography, microencapsulation, films or even as an additive in finishing products for the leather industry.