© Color. Technol., 121 (2005) 291 Web ref: 20050601 Coloration Technology Society of Dyers and Colourists Dyeing behaviour of cotton fabric bioscoured with pectate lyase and polygalacturonase M Calafell, a, * B Klug-Santner, b G Guebitz b and P Garriga a a Chemical Engineering Department, UPC-ETSEIT, Colom 11, 08222 Terrassa, Spain Email: margarita.calafell@upc.es b Institute of Environmental Biotechnology, Graz University of Technology, Austria Received: 12 May 2005; Accepted: 16 August 2005 Bioscouring of cotton is normally carried out using pectinases having pectate lyase activity. The present study has examined the influence of pectate lyase and hydrolase on the surface of cotton fibre. Dye uptake by cotton scoured with polygalacturonase is found to be much lower than that scoured with pectate lyase, Pectate lyase gave better dye exhaustion at 90 °C. The difference in dye exhaustion after scouring with sodium hydroxide, polygalacturonase or pectate lyase, may be due to variation in the amount of surfactant retained by the fibre, as this hinders dye uptake. This was particularly the case with polygalacturonase. Reduced numbers of free carboxy groups on the fibre surface could indicate lower pectin content. On the other hand it could, however, be due to the esterification of carboxy groups in the pectin by hydroxy groups in the surfactant. Introduction Bioscouring is a relatively new technique for removing pectin, proteins and waxes from raw cotton by means of enzymes. This technique has advantages compared with chemical scouring using sodium hydroxide, including energy savings and reduced salt concentration in the wastewater. In addition, less damage is caused to the fibre and as a result less reduction in fibre strength. The use of pectinases in bioscouring offers advantages over other enzymes, including cellulases, lipases and proteases [1,2]. Most current bioscouring processes for cotton employ alkaline pectinases with pectate lyase activity [3,4]. On the other hand, a number of micro- organisms are found in nature which produce pectinases with activity in acid media. Pectinases of this type, for example polygalacturonase, exhibit hydrolase activity and are used widely in the food processing industry [5]. The fact that hydrolases are not generally used in the textile field has been due to lack of understanding of the pectin cleavage on bioscouring. Pectin acts as a net which traps molecules such as glycoproteins, waxes and xyloglucans in a non-covalent manner within the cuticle of the cotton fibre [6]. The structural complexity of cotton and its degree of polymerisation provide a protective barrier to the cotton fibre. It is worth describing briefly the nature of the structure since this is important in bioscouring. Pectins are a family of complex polysaccharides, usually amorphous, with a degree of polymerisation around 200–400 units [7]. Three pectic polysaccharides, homogalacturonan, rhamnogalacturonan-I and substituted galacturonans, have been isolated from the primary cell wall and their structures characterised [8]. The main chain of homogalacturonan contains 1,4-linked α-D-galactosyluronic acid residues. Substituents are located at the C-2 or C-3 position of the main chain. Substituents may be non-sugar (acetyl) or sugar- like (D-galactose, D-xylose, L-arabinose and L-rhamnose). In cotton fibres, 60–75% of the chains of polygalacturonic acid can be methylated. Rhamnogalacturonan-I contains a backbone of repeating disaccharides [-4)-α-D-galacturonic acid-(1,2)-α-L-rhamnose-(1-]. The galacturonic acid residues in the backbone can be O-acetylated at C-2 and/or C-3. [9]. Rhamnogalacturonan-I is solubilised from cell walls by polygalacturonases [10]. Substituted galacturonans are a diverse group of polysaccharides containing a backbone of linear 1,4-linked α-D-galacturopyranosyluronic acid residues [11]. The polymer is highly methylated in the main chain of polygalacturonic acid and has a greater number of side- chains [12]. Due to the vulnerability of these polymers to enzymes, pectic enzymes can cause plant tissue maceration, cell lysis and modification of cell wall structure [13]. Pectic enzymes are produced in large quantities by many plant-associated micro-organisms. Pectinolytic micro- organisms produce a battery of pectic enzymes differing in substrate preference, reaction mechanism and mode of action. Pectate lyase, pectin lyase and exo-polygalacturonate lyase cleave by β -elimination and generate products having 4,5-unsaturated residues at the non-reducing end (A in Scheme 1). Polygalacturonase and exo-poly- α- D- galacturonosidase cleave by hydrolysis (B in Scheme 1). Pectinesterase de-esterifies pectin to pectate and methanol. Pectate lyase, pectin lyase, and polygalacturonase cleave internal glycosidic bonds and generate a series of oligomeric products. exo-Polygalacturonate lyase and exo-poly- α-D- galacturonosidase attack chain termini, releasing only digalacturonates, and reduce the viscosity of solutions containing pectic polymers more slowly than the endo- attacking enzymes. Pectin lyase attacks pectin (poly- methoxygalacturonide); the other enzymes attack pectate (polygalacturonate) [13]. In the present study, two different commercial pectinase