Pre-tanning of Goatskin by Minimizing Chemical Usage using Crude Protease Enzyme for Crust Leather Preparation

Abstract

Abstract The traditional use of beam house chemicals such as lime and sodium sulfide for hair removal from hide/skin results in significant environmental drawbacks, including excessive water consumption, hair digestion, and solid sludge discharge into effluent. In this study, we have isolated proteolytic bacteria belonging to Alcaligenaceae sp. (GenBank accession number OP456525) from the soil of a tannery solid waste dumping yard. These bacteria exhibited robust protease production with optimal activity at 50°C and pH 7.0. By utilizing the crude protease, we achieved complete unhairing of goatskin and enhanced fiber opening, effectively eliminating three highly polluting stages (liming, deliming, and bating) from conventional leather processing. Protease-based unhairing demonstrated significant reductions in pollution load, with decreases of 60.1%, 98.54%, and 61.63% observed in dissolved solids (TDS), suspended solids (TSS), and total solids (TS), respectively, compared to conventional liming methods. The crust leathers thus produced via protease-based unhairing exhibited approximately 25% increased chromium uptake. Furthermore, enzyme treatment led to improved hydrothermal stability and enhanced physico-mechanical properties, including tensile strength, tear strength, and grain crack strength. FESEM images confirmed that the fiber structure of the samples treated with the protease is more compact than conventional leather. Employing a clean, enzyme-based unhairing procedure utilizing Alcaligenaceae sp. crude protease enables the production of eco-leather without the use of sodium sulfide, lime, ammonium-based deliming agents, or bating agents, thereby enhancing occupational health and safety while promoting a more environmentally friendly and sustainable approach to leather production.