Estudo da produção in vitro de enzimas ligninocelulolíticas por fungo basidiomiceto cultivado sob fermentação sólida de resíduos vegetais

Abstract

(Study of in vitro production of lignocellulolytic enzymes by basidiomycete fungus in solid substrate fermentation of plant wastes). Lignocellulosic residues has been used as a source of fermentable sugars in an attempt to reduce the costs of producing bioproducts which are obtained from glucose and/or cellulose. These wastes are composed of cellulose and hemicellulose, which are strongly linked to lignin. Bioconversion of ligninocelulosic requires delignification to liberate cellulose and hemicellulose from their complex with lignin. So, they can be hydrolyzed to simple free sugars (glucose and xylose), enabling the subsequent fermentation to obtain various products such as ethanol and others. Several enzymes are involved in this process: lignin peroxidase, manganese peroxidase, laccase, cellulase and hemicellulase. Fungal enzymes show good results for degradation of lignin, allowing enzyme’s access to carbohydrates in the ligninocellulose conversion. In this work, 14 basidiomycetes from semi-arid of Bahia were evaluated for enzyme production. The fungus Trametes villosa showed the best results in that screening. Coconut shell, bagasse of sugarcane and sisal fiber (lignocellulosic materials abundant in the Northeast of Brazil) were used as substrate for the fungal growth. Experimental designs, including response surface methodology (RSM), were used in the optimization of culture conditions that favor the production of interesting enzymes. The best results were found for manganese peroxidase, whose optimum pH and temperature were determined. The optimized conditions for the secretion of this enzyme by the tested fungus were: bagassse of sugarcane, 80% moisture, pH 9.38, temperature of 20°C and 15 days of cultivation. The enzyme presented pH 4.5 as optimum whithout differences among tested temperatures from 20 to 90° C.