Rhizopus oryzae efficiently converts barley proteins into mycoprotein in solid state fermentation and improves food functionality of brewer’s spent grain

Vast amounts of beer is produced worldwide resulting in a massive side stream of Brewer’s spent grain (BSG), which is a protein-rich biomass with high fiber content and an optimal moisture content for fungal solid-state fermentation (SSF). BSG is mainly used for ruminant feed and biogas production but can and should – from a sustainability viewpoint – be used as food instead. Progress has been made towards making BSG palatable as flour or crackers, however its minimal food functionality limits its use in food. We have utilized the “tempeh” fungus Rhizopus oryzae for SSF of BSG. We have shown that SSF with R. oryzae makes it possible to increase the protein content and at the same time introduce an increased degree of functionality. Our results showed a significant change in protein composition after 90 hours of fermentation in a controllable bioreactor with 95 % of the protein being mycoproteins and only 5 % being barley proteins. We have applied an optimized protocol for protein extraction to produce protein-rich extracts from the fermented BSG. The protein-rich extract exhibited enhanced functionality compared to crude fermented-BSG, highlighting its potential as a sustainable and versatile ingredient for food applications. Furthermore, we sequenced our strain via nanopore sequencing to better identify biosynthetic gene clusters coding for mycotoxin production. No mycotoxin clusters were found confirming the safety of using R. oryzae for food applications. The protein-rich extract exhibited enhanced functionality compared to crude fermented-BSG, highlighting its potential as a sustainable and versatile ingredient for food applications.