Metabolomic study of the soybean pastes fermented by the single species Penicillium glabrum GQ1-3 and Aspergillus oryzae HGPA20

Penicillium glabrum GQ1-3 and Aspergillus oryzae HGPA20 isolated from home-made soybean pastes were separately inoculated into soybean paste subjected to brine fermentation for 90 days. The amino acid nitrogen contents of the two fermentation systems were detected every 10 days, and both reached the maximum level at 40 days. The samples fermented for 40 days were analyzed via gas chromatography-time of flight mass spectrometry. Using univariate, multivariate and KEGG analyses, 72 differential metabolites were obtained, and 7 metabolic pathways closely related to fermentation were screened. The relative contents of 2-oxoglutarate, ornithine, glutamine, and citrulline were higher in GQ1-3, whereas those of L-homoserine, aspartic acid, and asparagine were higher in HGPA20. These findings indicate that a-ketoglutaric acid-derived amino acid synthesis is preponderant in GQ1-3, whereas oxaloacetate-derived type is predominant in HGPA20. The different pathways of amino acid synthesis lead to the distinct nutrients and umami substances in the fermented soybean pastes.