Solid-state fermentation with mushroom mycelium elevates plant protein quality and umami taste

Solid-state fungal fermentation (SSFF) offers a low-tech, low-energy, and minimal processing method to enhance the protein content and quality of foods. This study evaluates the potential of SSFF executed with mycelium of edible basidiomycetes to improve both nutritional and sensory qualities of brown rice, brewer's spent grain (BSG), and lupin. The conventional tempeh fungus, Rhizopus microsporus var. oligosporus, was used as control. Different substrate-fungus combinations varied in impact on flavour and protein quality. SSFF improved the protein quality and umami taste of brown rice and mainly improved in umami taste of lupin, while fermentation of BSG with basidiomycetes even decreased protein quality. Basidiomycetous SSFF products exhibited higher umami potential, with equivalent umami concentrations (EUC) reaching 159 g MSG-eq/100 g DW, surpassing the values found for R. microsporus-fermented products. In terms of substrates, the protein content increased most in brown rice fermentations, while the EUC and protein quality increased most in lupin. Protein quality and content increased more in basidiomycetes, indicated by the up to 35.1% increase in the protein digestibility corrected amino acid score of the limiting amino acid lysine and a 36.4% rise in utilizable amino acids. Basidiomycetous SSFF thus offers a promising approach to upgrade low-quality plant proteins into more palatable and nutritious foods.