Pretreatment of wheat straw by white-rot fungi for enzymic saccharification of cellulose

Abstract

Of 19 white-rot fungi tested, Pleurotus ostreatus, Pleurotus sp. 535, Pycnoporus cinnabarinus 115 and Ischnoderma benzoinum 108 increased the susceptibility of straw to enzymic saccharification, thus indicating that these organisms degraded or modified the lignin component. After pretreatment cultivation with Pycnoporus cinnabarinus 115, as much as 54.6% of the residue was converted to reducing sugars in the enzymic saccharification process. Phanerochaete sordida 37, Phlebia radiata 79 and two unidentified fungi also gave better results than Polyporus versicolor, a non-selective reference fungus. After 5 weeks pretreatment with Pleurotus ostreatus, 35% of the original straw was convertable to reducing sugars, 74% of which was glucose; compared with this, only 12% of the untreated control straw was convertable to reducing sugars, 42% of which was glucose. After an alkali pretreatment (2% NaOH, 0.4 g NaOH/g straw, 10 min at 115°C) enzymic saccharification converted 41% of the straw to reducing sugars, of which only 50% was glucose. In the best cases the efficiency of biological pretreatment was comparable with that of alkali treatment, but resulted in a higher proportion of glucose in the hydrolysates. Pretreatment by the fungi Phanerochaete sordida 37 and Pycnoporus cinnabarinus 115 in an oxygen atmosphere reduced the treatment time by approximately 1 week. However, the economic feasibility of a non-optimized biological pretreatment process is still poor due to the long cultivation times required.