Metatranscriptomics and HS-GC-IMS unveils the disparities in gene functions, metabolic traits, and volatile metabolites between highly-preserved and easily-spoiled soybean pastes

Traditional fermented soybean paste samples display distinct highly-preserved (HP) and easily-spoiled (ES) characteristics. This study delves into the metatranscriptomic and volatile metabolites investigations of HP and ES samples to explore their influencing on the quality of soybean pastes. The results showed that Firmicutes were predominant in HP soybean pastes, in which genus Bacillus having highest abundance, while Proteobacteria was most abundant in ES ones, with Citrobacter, Salmonella, and Escherichia top abundant. Amino acid transport and metabolism, carbohydrate transport and metabolism, energy production and conversion held most abundant gene functions. HP and ES samples had significant differences in biological processes, cellular components, and molecular functions revealed with GO functional enrichment analysis. Furthermore, ABC transporters and aminoacyl-tRNA biosynthesis were among significantly enriched pathways in HP samples, and biosynthesis of secondary metabolites and chlorocyclohexane and chlorobenzene degradation in ES samples disclosed with pathway enrichment analysis with KEGG. Among ES downregulated genes, the most function-related genes belonged to Bacillus. The selected genes data with qRT-PCR effectively validated the metatranscriptomic results. For volatile compounds, HP had much more 1-octanal, 1-octen-3-ol, ethanol, limonene, ethyl lactate and ethyl acetate, ES soybean pastes had higher levels of propanal, hexanal, 3-methyl butanoic acid, methanol. The research furnishes a comprehension of the microbes, functional genes and volatile metabolites involved in soybean paste preservative properties, which may help improve the quality of soybean paste products.