Changes in metabolite profiles in solid fermentation of glutamate waste treatment solution by Aspergillus niger and Candida tropicalis

AIMS: Glutamate wastewater poses a great environmental challenge to the monosodium glutamate production industry. However, its treatment solution is rich in crude protein, which has the potential to be developed as a new protein source for animal feed. METHODS AND RESULTS: Given that the fermentation process generates functionally different metabolites, this study innovatively utilized two strains of feed microorganisms, Aspergillus niger and Candida tropicalis, to perform solid-state fermentation of glutamate wastewater treatment solution. The aim was to investigate and analyse the metabolite profiles during fermentation. The significant differences in metabolite profiles between the samples were determined using correlation analysis, principal component analysis, orthogonal partial least-squares discriminant analysis, variable importance in projection analysis, Kyoto Encyclopaedia of Genomes, and Human Metabolome Data Bank analysis. These variations were mainly manifested in essential feed components, such as amino acids, peptides, and their analogues. These included Ile-Pro-Asn, Pro-Gly-Val, alanylvaline, histidylisoleucine, Lys-Leu-Tyr, Ile-Arg, glycyl-leucine, leucyl-lysine, N-palmitoyl histidine, alanylisoleucine, l-glutamate, N-methylisoleucine, Isoleucylproline, dl-m-tyrosine, Isoleucyl-threonine, phenylalanine amide, carboxyethyllysine, N6-acetyl-l-lysine, citrulline, N-alpha-acetyl-l-lysine, N(6)-methyllysine, and l-aspartate-semialdehyde. CONCLUSIONS: This study investigates the metabolite profiles of glutamate wastewater treatment solutions after co-fermentation with A. niger and C. tropicalis using solid-state fermentation. These findings provide a new strategy for efficiently utilizing glutamate wastewater treatment solutions.