Potential for combined production of food and biofuel: Cultivation of Pleurotus pulmonarius on soft- and hardwood sawdusts

This study aimed at developing an integrated process of production of edible summer oyster mushroom (Pleurotus pulmonarius) and preprocessing of the substrate lignocellulose for producing 2nd-generation biofuels based on softwood. Sawdust-based mushroom substrates of softwood spruce (Picea abies) versus hardwood alder (Alnus glutinosa) as a reference were used for production of summer oyster mushrooms. The substrates had been either hot-air pasteurised or steam sterilised before growing the mushroom. The potential of using spent substrate (SMS) after harvest for biofuel production was evaluated by examining the lignocellulosic composition and enzymatic convertibility. The biological efficiency of the substrates ranged 14.0–33.8% and no significant difference was observed between the treatments. The fruiting bodies had similar total protein concentrations ranging between 26.0 and 28.5% regardless of differences in treatments. The average mass degradation of Klason lignin and acid soluble lignin in the substrates after mushroom production were 35.0 and 22.6%, respectively. Glucan, the major carbohydrate component, was initially present in concentrations ranging from 24 to 29% of total dry matter and with similar concentrations observed in both alder-based and spruce-based substrates. After mushroom production, a significant difference was observed between the substrates with the lowest consumption of glucan, 3.9% of the initial mass, in the spruce-based substrate. The selective degradation ability of P. pulmonarius on the lignin fraction, rather than the cellulose component of softwood, is suggested in the present study. Between 84 and 126 g glucose was yielded per kg of dry SMS, spruce based substrates resulted a higher yield than alder substrate from enzymatic saccharification of the spent substrates. The heat treatment of the mushroom’s substrate had in general a minor impact on the mushroom production and fungal pretreatment of the substrates; hot-air pasteurisation is apparently more energy efficient method than steam sterilisation.