Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/17/2006
Publication Date: 11/1/2006
Citation: Marmer, W.N., Dudley, R.L. 2006. The Oxidative Degradation of Keratin (Wool and Bovine Hair). Journal of American Leather Chemists Association. 101(11):408-415. Interpretive Summary: An early stage in the conversion of hides into leather is the removal of hair from the hides. This has been done traditionally using toxic and environmentally unfriendly processes employing the chemical agent sodium sulfide. Oxidizing agents are alternative and more benign agents. In the past few years we have investigated the effectiveness of such alternatives. In the current study we examined those processes to determine if they all worked by a common mechanism. We applied such techniques as NMR spectroscopy, mass spectrometry, and solubility studies on hide samples and hair. Not only did the results point to a common mechanism, but they demonstrated that a consequence of alkaline dehairing – so-called hair immunization, which renders the hair resistant to dehairing – is of no consequence when applying the alternative oxidative systems. The results should encourage the replacement of sulfide-induced dehairing in our tanneries and those abattoirs that conduct their own dehairing.
Technical Abstract: In our development of multiple formulations for alkaline oxidative dehairing, using perborate, percarbonate, and hydrogen peroxide/cyanate systems, we wondered whether all the oxidative dehairing reactions could be described by a single reaction mechanism. The present study investigated the parameters of base concentration, oxidant, and reaction time, and sought evidence for hair immunization (the formation of protein species insoluble in alkaline sulfide) and cystine oxidation. The base likely played two roles, a catalyst for the hydrolysis of the polypeptide backbone and an aid in the swelling of the hair shaft. The disulfide linkages in cystine were oxidatively cleaved by the oxidizing agent and the reaction mechanism was the same for all of the oxidative systems. MALDI TOF/TOF spectrometry indicated that at least some of the cysteine in solubilized keratin liberated from treatment of alkaline peroxide/cyanate remained intact (unoxidized), but proton NMR spectroscopy showed the oxidation of cystine to cysteic acid for all oxidizing systems studied. Base was effective in hydrolyzing the keratin, but the addition of an oxidizing reagent (perborate) increased the amount of hair (wool) solubilized and decreased the amount of solubilized keratin with a MW> 3.5 KDa. The increased rate of alkaline solubilization of wool by incorporation of oxidizing agents suggested that the cleavage of the disulfide linkage further allowed the hair to swell and take up water (and base).