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Research Project: Improving the Quality of Animal Hides, Reducing Environmental Impacts of Hide Production, and Developing Value-Added Products from Wool

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Title: Soluble collagen approach to a combination tannage mechanism

Author
item Brown, Eleanor - Ellie
item Taylor, Maryann
item Liu, Cheng Kung - Ck

Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2015
Publication Date: 4/1/2016
Citation: Brown, E.M., Taylor, M.M., Liu, C. 2016. Soluble collagen approach to a combination tannage mechanism. Journal of American Leather Chemists Association. 111(4):141-147.

Interpretive Summary: The U.S. meat industry currently produces approximately 35 million cattle hides annually as a major byproduct. The conversion of these hides into leather, makes them the most valuable byproduct of the U.S. meat industry. Although complex salts of Cr(III) are currently the most effective and prevalent tanning agents, there is current interest in tannages that use other minerals in combination with vegetable tannins. The mechanisms of combination tanning are poorly understood. In previous research, ARS scientists developed protocols using powdered hide to elucidate tanning mechanisms. This study used a solution model to examine the interactions of aluminum salts and vegetable tannins separately and combined with collagen, the primary constituent of the hide. Aluminum was thought to react more strongly with tannins than with collagen, and the extraction of water from the collagen solution in the formation of an aluminum/tannin complex suggests that the lowering of water activity around the collagen may play a role in stabilizing a collagen/tannin/aluminum tannage. Aluminum also reacted separately with collagen to form high molecular weight complexes. These findings will contribute to a general mechanism for tanning and the development of new tannages.

Technical Abstract: Although complex salts of Cr(III) sulfate are currently the most effective tanning agents, salts of other metals, including aluminum, have been used either alone or in combination with vegetable tannins or other organic chemicals. In the present study, the interactions of aluminum sulfate, and quebracho or chestnut tannins with collagen were investigated. A model system was devised to use soluble collagen in one compartment of an equilibrium dialysis cell, and solutions of mineral or polyphenolic tanning agents in the other compartment. This study, by focusing on the effects of tanning agents on soluble collagen, rather than on intact hide, or even powdered hide, gives a somewhat different perspective on the tanning process. The extraction of water from the collagen solution in the formation of aluminum/tannin complexes suggests that the lowering of water activity around the collagen may play a role in stabilizing a collagen/tannin/aluminum tannage. The most interesting finding is that aluminum which has little effect on collagen helical structure and stability does appear to connect collagen molecules in some manner to produce high molecular weight species that do not separate under the conditions of SDS PAGE. Comparison of the interactions of various combinations with collagen is expected to provide insight into a more generalized mechanism for tanning.