Towards environmentally friendly skin unhairing process: A comparison between enzymatic and oxidative methods and analysis of the protein fraction of the related wastewaters

A huge amount of by-products, wastes and chemicals are generated during leather processing, originating environmental problems due to the great amount of pollutants released, in particular for the unhairing step. Due to this reason, several strategies are studied today to reduce its impact. In this work two different methods, developed at a pilot scale level in semi-industrial reactors, were compared: an unhairing method based on proteolytic enzymes (Alcalase from Bacillus licheniformis) and an oxidative one based on chemical agents (sodium hydroxide and hydrogen peroxide). The efficiency of the unhairing was evaluated in both cases. The impact of both treatments on the nitrogen fraction in wastewaters was determined in order to assess the suitability of these by-products for a possible recovery in food/feed industry: the protein amount, the total and free amino acids, peptides and the percentage of amino acid racemization were determined on broths, washing residues and skins. The results indicated that both methods have the potential to be more sustainable alternatives to the current ones. The oxidative method seemed to be the most efficient and less expensive unhairing methodology, and does not require a further step after the end of the treatment as in the case of enzymatic unhairing process. On the other side, the wastewaters of enzymatic treatments, quite rich in good quality proteins, could be recovered for feed/food formulations, whereas the wastewaters coming from the oxidative treatments, due to the oxidative damage, only for lesser value applications.