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.
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.