Enzymes are bio-catalysts and are used in several industrial processes since nineteenth century. Its use in textile industry is an example of industrial or white revolution. Enzymes, due to their non-toxic and eco-friendly characteristics, have gained wide applications in textile industry. Not only they are highly specific, efficient and work under mild conditions but also they help reduce process times, save energy and water, improve quality of product and reduce pollution. As a result they are rapidly gaining global recognition as important requirement for textile industry.
Commercially enzymes can be obtained from three primary sources, animal tissues, plants and microbes. However, these naturally occurring enzymes are not produced in sufficient quantities to be readily used in industrial applications. Hence, microbial strains producing the desired enzyme are cultured and optimised i.e. fermentation, to obtain enzymes in sufficient quantities for their commercial use in textile industry. The enzymes used in the textile industry are amylases, cellulases, pectinases, lipases, catalases, proteases, xylanases etc. and are mainly used for processing of the textiles i.e. preparatory and finishing of the goods. Some of the applications include removing of starch, bleaching, degrading lignin, fading of denim and non-denim, removal of peroxidises, finishing of wool, decolouration of dyestuff, bio-scouring, bio-polishing, wool finishing, etc. (Shenai, 1990; Nalankilli, 1998; Barrett et al., 2003;Cavaco and Gubitz, 2003; Chelikani et al., 2004).
CLASSIFICATION AND PROPERTIES OF ENZYMES USED IN TEXTILE INDUSTRY
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Enzymes are very specific toward catalysing the substrate. Hence these are classified on the basis of their catalytic functions in six broad categories:
EC1 Oxidoreductases: catalyze oxidation and or reduction reactions
EC2 Transferases: catalyze transfer of a functional group
EC3 Hydrolases: catalyze the hydrolysis of various bonds
EC4 Lyases: catalyse cleavage of various bonds by means other than hydrolysis and oxidation
EC5 isomerases: catalyse isomerisation changes within a single molecule
EC6 Ligases: joining of two molecules with formation of covalent bonds
Properties of enzymes exploited for use in industrial application:
Acceleration of the reaction rates by lowering the activation energy of the reaction.
Operating optimally under milder conditions of temperature, pH and atmospheric pressure.
Alternative for polluting, toxic and carcinogenic chemicals
High specificity towards substrate makes easy to control their activity
Biodegradable and do not produce toxic wastes.
Due to their high efficiency, specificity, property of working under milder conditions and biodegradability enzymes are well suited for various industrial applications.
ROLE FO ENZYMES IN TEXTILE INDUSTRY
Use of enzymes in various textile processing processes has greatly benefited textile industry with respect to both environmental impact and quality of product. There are 7000 known enzymes, but only 75 are commercially used in textile industry (Quandt and Kuhl, 2001) and most of them belong to hydolases and oxidoreductases families. The hydrolases family includes amylases, cellulases, pectinases, proteases, catalases and lipases/estarases and oxidoreductase family include laccase, peroxidises.
Amylases actson starch molecules and hydrolyses to give dextrin and small polymers of glucose units (Windish and Mhatre, 1965). These are classified according to the sugars they produced i.e. α-amylases and β-amylases. α-Amylases being produced from filamentous fungi and bacteria are mostly used in industries (Pandey et al., 2000). This enzymes are stable over wide range of pH from 4-11 and optimal activity is related to the growth conditions of the source microorganisms (Vihinen and Mantsala, 1989). In general, α-Amylases show's high specificity towards starch followed by amylase, amylopectine, cyclodextrin, glycogen and maltotriose (Vihinen and Mantsala, 1989).
1.1 Textile Desizing
Size is an adhesive substance used to coat the wrapping threads used in weaving of the fabrics made from cotton or blend. Starch and its derivatives are broadly used to size fabrics due to their easy availability, relative low cost and excellent film forming capacity (Feitkenhauer et al., 2003). Amylases are used to remove this sizing material and prepare the fabric ready for dyeing and finishing (Cavaco-Paulo et al., 2008). Earlier to the discovery of amylases, desizing was done by chemical treatment of fabric with acid, alkali or oxidising agents at high temperature. But, this technique was inefficient in removing the starch which resulted in imperfections in dyeing and also degradation of cotton fibre. Amylases are commercially used for desizing fabric due to its efficiency and specificity and its effectiveness in completely removing the size without affecting the fabric (Cegarra, 1996; Etters and Annis, 1998). Starch is removed during washing in the form of water soluble dextrin and thus reduces the discharge of chemical waste into the environment.
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Cellulases are the hydrolytic enzymes that catalyses the breakdown of cellulose to smaller oligosaccharides and finally to glucose. These enzymes are commonly produced by soil-dwelling fungi and bacteria such as Penicillium, Trichoderma and Fusarium (Verma et al., 2007) and shows optimal activity in temperature range from 30C-60C. The applicationof cellulases in the textile industry begin in late nineteenth century with denim finishing. It alone accounts for 14% of the world's industrial enzyme market (Nierstrasz and Warmoeskerken, 2003).
2.1 DENIM FINISHING
Denim is high grade cotton and its washing is done in order to give a worn look e.g. stonewashing of denim jeans, in which the denim fabric id faded using sodium hypochlorite or potassium permanganate are used as pumice stones (Pedersen and Schneider, 1998) it resulted in damage to the fabric and machine. Introduction of cellulases have increased the productivity without affecting garment or the machine. Cellulases hydrolyses the exposed surface of dyed (indigo) fabric leaving the interiors intact, partial hydrolyses of the surface results in removal of dye and leaves a light area. Most of the cellulases are produced from fungi, but cellulases from bacterial and actinomycetes origin are now studied with regard to its use in bio-stoning of denim. Cellulases used for washing of the denim can be further classified on the basis of optimal pH required for its maximum efficiency; as neutral cellulases operating at pH 6-8 and acidic cellulases acting at pH 4.5-6.
Washing of cotton and other natural and man-made cellulosic fabrics, besides denim, such as linen, hemp, rayon and viscose by enzymatic activity of cellulases to improve final appearance is done by bio-finishing or bio-polishing processes (Videbaek and Andersen, 1993). The process helps in preventing the formation of ball of fuzz called pill on the surface of the garment, this formation usually results in unattractive, knotty fabric appearance. Cellulases, hydrolyses the microfibrils protruding from the surface of the fabric which tends to break off leaving a smoother surface.
Bio-finishing may be an optional step for upgrading cotton fibrics, but is very important step in prevention of pilling or fibrillation during finishing of lyocell fabrics (Cavaco-paulo et al., 2008). Similarly, Carrillo et al. (2003) stated that cellulases can be used for viscose type regenerated celloloses like viscose and modal. Yachmenev et al. (2002) showed the use of ultrasound as an efficient way to improve the enzymatic activity in bioprocessing of cotton.