4.1.2. Biological pretreatmentBiological pretreatments have been mostly been associated with the action of fungi capable of producing enzymes that can degrade lignin, hemicellulose, and polyphenols. White- and soft-rot fungi have been reported to degrade lignocellulose material, with White-rot being the most effective at biological pretreatment of biomass (Lee 1997; Sun and Cheng 2002). Brown-rot fungi primarily attack cellulose, whereas white and soft-rot attack both lignin and cellulose via the production of enzymes such as lignin peroxidases, polyphenol oxidases, maganesse-dependent peroxidases, and laccases that degrade the lignin. Hatakka et al. (1993, 1994) reported the selective delignification of wood and wheat straw by selected white-rot fungi such as; Phanerochaete chrysosporium, Phlebia radiata, Dichmitus squalens, Rigidosporus lignosus, and Jungua separabilima. Lignin depolymerization by these fungi takes weeks to achieve significantresult but can be very selective and efficient (Hatakka 1994; Hatakka et al. 1993).
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