Valorisation of spent mushroom substrate by secondary microbial fermentation

Global mushroom production exceeds 45 million tonnes, involving growth on a lignocellulosic substrate. More than 70% of these mushrooms are considered wild mushrooms that are grown on a lignocellulose substrate. At the end of the growth cycle, the remaining spent mushroom substrate (SMS) is considered waste with little value and is often discarded. The limited information available on the fibre content remaining in SMS indicates that different white-rot fungi can result in significant differences in the hemicellulose and lignin content, which in turn may impact the second fermentation step. Secondary fermentation has found uses in the production of biofuels, as a preserved ruminant feed, for enzyme production, in the formation of microbial compounds, and as an amended fertiliser. Finally, achieving secondary fermentation of SMS could involve the development and use of larger-scale solid-state fermentation. This review article has shown that research into secondary fermentation of SMS has been a relatively new field occurring over the past 14 years.