Applicability assessment of a proteolytic fermentation broth to leather tanning and protein stain removal

The use of alkaline microbial proteases makes the industry more eco-sustainable, both in terms of reducing the consumption of chemical products and in terms of lowering effluent treatment costs.

A proteolytic Bacillus strain isolated from a tannery alkaline bath was used to produce extracellular proteases by submerged fermentation in bioreactor and the produced proteolytic broth was applied in leather tanning and protein stain removal.

The tanning process application consisted of using fermentation broth with 780 LVU (Löhlein–Volhard Unit) proteolytic activity on half-skin tanning, and the other half-skin was tanned using a commercial enzymatic bate (OROPON) with same proteolytic activity and tanning conditions.

The physical properties of the hide tanned using proteolytic broth and the hide tanned with commercial bate were assessed in terms of bursting load (kg) and bursting elongation (mm) for hides with two different leather thicknesses (2.4 mm and 1.6 mm). The hide tanned with the produced broth showed better physical tests of bursting (with elongation till 6.8 mm before bursting) than the one tanned with commercial proteases (elongation only till 6.3 mm) for same bursting load of 19 kg and 1.6 mm leather thickness. The thicker leather (2.4 mm) showed the same bursting elongation of 10 mm for a higher load (54 Kg) for the hide tanned with bulk proteases than commercial proteases.

Protein stain removal from cotton fabric (squares of cotton fabric with 4 cm sides with the centre stained with egg, blood, soya sauce and English sauce) was tested using the produced proteolytic broth and compared with the use of water (blank), or a commercial detergent, under the same agitation at room temperature. The proteolytic broth showed better blood and egg stain removal than water or the detergent.

Produced proteases can be used in protein residue and effluent treatments. Applications showed potential for use in the bioeconomy and for green chemistry.