Using enzymes produced by bacteria, scientists at the Chennai-based CSIR-Central Leather Research Institute (CSIR-CLRI) have removed hair from goat skin used in leather industry. This method was found to be safer and more environmental friendly than the conventional method of unhairing using lime and sodium sulphide. The results were published in Environmental Science and Pollution Research.
These chemicals pose serious environmental problems as the effluent is rich in suspended solids. Besides contamination, these effluents may also release noxious gases like hydrogen sulphide causing a serious health hazard.
Microbial enzyme
A novel bacterium ( Bacillus crolab MTCC 5468) was isolated and used for the study. This bacteria produces proteases (enzymes produced to break down protein) which have been found useful in unhairing processes. “The bacteria were isolated from the soil around the Buckingham canal close to Adyar region, Chennai, where a meat stall was located earlier. So the soil there was rich in proteinaceous matter making it an ideal spot for isolation of bacteria. Among the hundreds of isolated bacteria, the bacterium with highest ability to breakdown proteins (proteolytic activity) was selected and used,” explains Dr. Chellan Rose was earlier with CLRI and one of the corresponding authors of the paper.
To extract the enzyme from the bacteria, scientists fermented wheat bran using the bacteria. The enzyme showed high proteolytic activity, which was 3.5 times greater than any reported for bacterial proteases.
Enzyme evaluation
The effect of the enzyme on goat skin soaked in water was tested. Crude enzyme was added in different concentrations to the skin and let to soak. The enzyme was able to remove hair completely within four hours. According to J. Durga, at CLRI and one of the authors of the paper, the enzyme was stable over a wide range of alkaline pH (8 to 11).
The tensile strength, tear strength, elongation and shrinkage temperature of the leather were tested after further processing. The strength was found to be considerably better than leather processed by chemical method. The smoothness, fullness and texture were marginally better than the chemically processed ones.
The enzyme was found to remove hair completely, leaving no trace of any keratinous material. Microscopic study showed that the protease was able to penetrate much efficiently into the skin matrix and remove even the hair root.
“The environment friendly method should not compromise on quality. We are trying to change centuries-old, time-tested method of hair removal. The main aim was elimination of pollution without altering the product and we found that our enzyme treatment not only reduced pollution but also produced better quality leather compared with the chemically treated ones,” explains Dr. C. Muralidharan, Chief Scientist at the Leather Processing Division, CLRI and one of the corresponding authors of the paper.
Effluent testing
The waste water after treatment was tested for the pollution load. The use of enzymes showed significant reduction in several parameters —biological oxygen demand (22%), chemical oxygen demand (58%), total dissolved solids (39%) and total suspended solids (22%) — compared with the chemical method. “The hydrogen sulphide that may form due to conventional unhairing process is a neurotoxin. This process lowers the environmental damage without altering the quality of leather,” says Mr. A. Ranjithkumar, research scholar at the institute and the first author of the paper.
