| dc.description.abstract | Spent mushroom substrate (SMS) is a leftover lignocellulosic biomass from mushroom cultivation that is rich in cellulose, hemicelluloses, lignin, and other biological components, making it a potential renewable resource for bioconversion processes for producing biofuels and other bio-based products. In this study, the enzymatic saccharification of SMS from two commercially important mushrooms, shiitake (Lentinula edodes) and oyster (Pleurotus ostreatus), cultivated on conventional (birch or oak sawdust) and non-conventional (spelt, wheat, oat straw, and coffee chaff) initial substrates, was investigated. The non-conventional oyster SMS is characterized by higher cellulose (up to 41.8% (w/w) in oat straw), lignin (32.6 % in wheat straw), water extractives (22.5% in oat straw), ethanol extractives (5.4% in the SMS containing coffee chaff), and ash content (13.8% in oat straw) compared to conventional SMS. For enzymatic saccharification, two commercial enzymes (Cellic CTec2, Trichoderma cellulases) and one experimental enzyme (ExpC) were used. Using Cellic CTec2, the analytical enzymatic saccharification of shiitake SMS resulted in digestibility of cellulose and xylan over 90 and 70% (w/w), respectively). An improved digestibility was observed when the extractive compounds were removed. The enzymatic digestibility of oyster mushroom SMS was lower than that of shiitake SMS. Hydrothermal pretreatment at 175ºC following either non-isothermal or partially isothermal heating regimes, was performed to improve the enzymatic saccharification of oyster mushroom SMS. Around 85-87% of the initial cellulose was recovered in the solid fraction after hydrothermal pretreatment. Hydrothermal pretreatment of oyster mushroom SMS at 175ºC improved enzymatic digestibility yielding solids with 60.0% and 55.7% cellulose and lignin content. Preparative enzymatic saccharification (PES) was performed using Cellic CTec2, validating the analytical results at a larger scale and showing effective cellulose and xylose saccharification from SMS compared to Cellic CTec3. In conclusion, SMS from shiitake and oyster mushrooms are promising sugar sources for microbial fermentations to end products of interest. The polysaccharides contained in shiitake SMS are readily hydrolysable, while those contained in oyster mushroom SMS require being pretreated to achieve a good saccharification. | |
