In this work is described the isolation of a new proteases-producing strain of Bacillus subtilis, screened from aerobic tannery sludge, to be applied in leather production. The optimization of culture conditions to enhance the proteolytic activity was carried out using central composite design. The enzymatic extract was characterized and the hide unhairing and the inter-fibrillary removal capabilities of the enzymatic extract were evaluated by scanning electron microscopy and by the determination of proteoglycans and glycosaminoglycans. The leather quality obtained with this enzymatic preparation was assessed for possible damages to hide collagen by measuring the amount of hydroxyproline released into the reaction medium. Temperature was the most significant factor for culture conditions optimization. The crude enzymatic extract showed the best values for proteolytic activities at pH 9 and 10, temperature between 37 and 55 °C, and showed good thermal stability up to 45 °C. The treated hides presented few remaining hairs; for the enzymatic process, the removal of inter-fibrillary proteins was approximately fourfold for glycosaminoglycans and sixfold for proteoglycans, when compared with the conventional unhairing process. The enzyme application was successful for hide treatment, suggesting that this enzymatic preparation can be used in an environment-friendly leather production to replace the conventional chemical process.
Screening and isolation of a new Bacillus subtilis strain and production of its proteases for leather unhairing are described. B. subtilis strain BLBc 11 was isolated from the aerobic sludge of a tannery. Optimization of enzyme production by this bacterium was carried out using the Plackett-Burman and central composite design. Unhairing and inter-fibrillary removal capabilities were evaluated by scanning electron microscopy and determination of proteoglycans and glycosaminoglycans. Crude enzymatic extracts of B. subtilis BLBc 11 cultures were applied for the unhairing process of hides with excellent results, suggesting that this safe enzymatic preparation can replace the toxic chemicals commonly used in this process.
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