In recent years the industries have seen a growth in the use of biotechnology, using processes like biocatalyst and biotransformation. Some advantages are: commonly the reaction or biotechnological processes occur at low temperatures and at atmospheric pressure, the process has a high space-time yield, renewable ingredients and in many cases there is reduction of environment impact. In leather production, biotechnology, mostly using enzymes, can be applied in different steps of process: soaking, unhairing, bating, dyeing, degreasing or in effluent and proteinaceous solid wastes treatment.
Soaking
Soaking is the first important operation in leather processing. It is done by using amylolytic, lipolytic and proteolytic enzymes. Specific protease and lipase enzymes enhance water uptake by breaking down soluble proteins inside the matrix, thus facilitating removal of salts, hyaluronic acid, disperse fats and oils together with dirt and other contaminants present in the skin. It reduces the wrinkles in leather and thus loosens the scud. It also enhances the opening of fibre structure. The soaking process helps in bringing the best quality of leather since it cleans hides and skins by removing dirt, flesh, blood etc and re-hydrates skin back to state of green hides.
Un-hairing
Un-hairing is the process of removing hairs and furs from the skin or hides without causing any grain damage. Conventional process of un-haring involves the use of lime and sodium sulphides which are responsible for causing pollution load. Enzymatic un-hairing is suggested as an environmentally friendly alternative to the conventional chemical process. With this enzymatic process, it is possible to reduce the chemical exposure and enhance the softness and area yield. The enzyme which is used for un-hairing is protease. The use of chemicals will completely dissolve the hair but the enzyme helps in filtering out the hair. This current process helps in improving the strength properties of the leather with greater surface area and provide eco-friendly environment to the workers.
Fibre opening mechanism
Fibre opening enzymes are provided for the mechanism which seems to reduce the pollution load and need for water treatment thus proving cost effective. The collagen is bound by proteoglycans which contain protein and glucose linked by the glycosidic linkages. This enzyme based fibre opening mechanism follows the bio-processing method which is totally different from conventional chemical based process. Carbohydrases are the enzyme used in fibre opening that degrades specifically the proteoglycans that opens the fibre for entry of water which causes swelling. Removal of proteoglycans results in softness. In conventional process, lime is employed for fibre opening which spoils the environment by causing pollution. Hence this method helps in reducing the lime sludge problems.
Bating
Bating is an important process in which enzymes plays a very crucial role whose purpose is loosening and peptization of the non collagenous skin structure through the removal of the residues of the interfibrillary proteins. Proteolytic enzyme is mainly used in the bating process. It helps in removal of lime and other non collagenous proteins that causes cementing which results in lack of flexibility.
Degreasing
Lipases are a type of enzyme that specifically degrades fat and so cannot damage the leather itself. Lipases hydrolyse not just the fat on the outside of the hides and skins, but also the fat inside the skin structure. Once most of the natural fat has been removed, subsequent chemical treatments such as tanning, re-tanning and dyeing have a better effect. The main advantages of using lipases are a more uniform colour and a cleaner appearance in the pelt. Lipases also improve the production of hydrophobic (waterproof) leather.
Waste processing
Effluent discharges from leather processing industries create health hazards and environmental problems unless these wastes are properly treated. Fleshings, the major solid waste generated at the pre-tanning operations were hydrolyzed using pancreatic enzymes. Trimmings obtained after liming had the alkalinity that corresponds to pH 10. So this is being treated with alkaline protease. This process is usually conducted at constant temperature 55ºC favorable for the enzyme. A combination of hydrolytic enzymes, viz. proteases, carbohydrases and lipases can be used.
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