Environmentally friendly hide unhairing: enzymatic hide processing for the replacement of sodium sulfide and delimig

In this work is described the use of an enzyme preparation produced by a new strain of Bacillus subtilis for hide unhairing aiming at completely replace the chemical process, which uses toxic sulfides and lime. The whole process was designed to be fast and cheap, by applying the crude enzymatic extracts of B. subtilis BLBc 11 cultures on the hides, with good results obtained in just 6 h of process. The treated hides were evaluated for their quality by optical microscopy and analyzes of inter-fibrillary proteins (proteoglycans and glycosaminoglicans). Undesired damage to the hide grain was evaluated by the determination of free hydroxyproline in the process liquor. Furthermore, the environmental impact of chemical and enzymatic treatments were compared, and the processes were evaluated by analyzing the chemical oxygen demand (COD), biological oxygen demand (BOD), total nitrogen, and sulfides in the residual wastewater, as the proprieties of the finished leather. COD reductions were of 42%, 100%, and 82% compared with the chemical process for the unhairing, deliming, and bating steps, respectively. The enzymatic unhairing process showed excellent results, with time reduction for unhairing of more than 50%, without the need for deliming, suggesting that this enzymatic preparation could be used to replace the chemical process.

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► We studied the use of proteolytic extracts from microorganisms isolated from tannery sludge for the unharing of hides.
► We evaluate the total replacement of sodium sulfide and lime for the enzymatic process.
► We compared environmentally the conventional unhairing process with the enzymatic one.
► The analysis of inter-fibrillary proteins and electronic microscopy of hides showed excellent results.