Lignocellulolytic enzymes and bioethanol production from spent biomass of edible mushrooms using Saccharomyces cerevisiae and Pachysolen tannophilus

In this study, spent mushroom substrate (SMS) obtained from edible mushrooms (Agaricus bisporus and Pleurotus florida) was used as a potential biomass for lignocellulolytic enzymes (oxidative and hydrolytic enzymes), and bioethanol production was investigated. The activity of lignocellulolytic enzymes was analyzed in SMS collected at different stages of mushroom cultivation. The activity of oxidative enzymes (VP, MnP, LiP, and laccase) was higher during mycelial growth stage, and the activity of hydrolytic enzymes (CMCase, xylanase, and cellobiohydrolase) was observed maximum during the formation and development of fruiting bodies. Relative proportion of lignocellulosic components (lignin, cellulose, and hemicellulose) was analyzed in SMS taken from axenic and non-axenic conditions. The scanning electron microscopy along with X-ray diffraction and Fourier transform infrared spectroscopy analysis of SMS showed strong alterations in the lignocellulosic fibers caused by the enzymatic and non-enzymatic action of the fungus in the substrate after the vegetative growth and fruiting stage of A. bisporus and P. florida. The hydrolysis with alkali (NaOH) and in-house produced partially purified enzymes were evaluated for SMS pretreatment to obtain maximal reducing sugar for bioethanol production. Maximum reducing sugar yield from SMS after pretreatment was 14.31 ± 0.49 mg/ml (A. bisporus) and 18.51 ± 0.56 mg/ml (P. florida). The fermentation efficiency of 76.13% and 58.12% was obtained from pretreated SMS of A. bisporus and P. florida at 30 ± 2 °C after 48 h incubation, by using co-culture of different sugar utilizing yeasts (Saccharomyces cerevisiae and Pachysolen tannophilus). The results suggested that SMS of edible mushrooms could be a cheap expedient substrate for sustainable bioethanol production with high lignocellulolytic enzymes recovery.