Improved nutritional value of surplus bread and perennial ryegrass via solid-state fermentation with Rhizopus oligosporus

Solid-state fermentation (SSF) is a sustainable method to convert food waste and plant biomass into novel foods for human consumption. Surplus bread crusts (BC) have the structural capacity to serve as an SSF scaffold, and their nutritional value could be increased in combination with perennial ryegrass (PRG), a biorefining feedstock with high-quality protein but an unpleasant sensory profile. SSF with Rhizopus oligosporus was investigated with these substrates to determine if the overall nutritional value could be increased. The BC-PRG SSFs were conducted for up to 72 h, over which time the starch content had decreased by up to 89.6%, the total amino acid (AA) content increased by up to 141.9%, and the essential amino acid (EAA) content increased by up to 54.5%. The BC-PRG SSF demonstrated that this process could potentially valorise BC and PRG, both widely available but underexplored substrates, for the production of alternative proteins.