Pretreatment of alfalfa stems by wood decay fungus Perenniporia meridionalis improves cellulose degradation and minimizes the use of chemicals

Enzymes of wood decay fungi can be exploited to degrade lignocellulosic wastes for sustainable production of bioethanol. Perenniporia meridionalis was tested for growing at different temperatures on stems of alfalfa. The process aims to produce fermentable sugars and can be divided into the following steps: (1) fungal treatment to degrade lignin, (2) microwave pretreatment in water or in phosphoric acid, and (3) enzymatic hydrolysis of cell wall carbohydrates. Thermogravimetric analysis assessed the biomass content of cellulose and lignin after the fungal treatment. Throughout all steps HPLC analysis of sugars, oligomers and by-products (furfural, hydroxymethylfurfural and acids) was performed. Scanning electron microscopy was used for visual inspection and characterization of the experimental material during the treatments. The P. meridionalis pretreatment enhanced the yield of fermentable sugars obtainable by enzymatic hydrolysis in samples subjected to microwave-assisted pretreatment in water, but not in those in acid medium. This is probably related to the very selective removal of lignin by P. meridionalis, exposing cellulose fibers without depleting them. Furthermore, microwave treatment in water produced less byproducts than in acid medium. By exploiting the P. meridionalis lignin degradation is therefore possible to avoid H₃PO₄ use during the alfalfa stem pre-treatment, reducing economic and environmental impacts.