Construction and validation of compound microbial systems in Allium chinense bulbs fermentation

This study explored the feasibility of targeted inoculation with functional core microorganisms to improve the overall quality of fermented Allium chinense bulbs. Using metagenomic sequencing, the research analyzed the physicochemical properties and dynamic variation in flavor compounds during spontaneous fermentation, and explores microbial community succession as well as its correlation with flavor formation. Two lactobacillus strains, namely Lactiplantibacillus plantarum NCU0011574 and Pediococcus pentosaceus NCU006281, were screened and identified owing to their glutamate production and flavor-generating capacities. Additionally, Pichia kudriavzevii BNCC335981, representing core yeast, was integrated with the aforementioned lactobacillus strains to establish two fermentation systems: a lactic acid bacteria (LAB) system (NCU0011574 and NCU006281) and an LAB-yeast system (NCU0011574, NCU006281, and BNCC335981). Spontaneous fermentation revealed that fructose, acetic acid, lactic acid, succinic acid, glutamic acid, and arginine are key flavor compounds, and pH serves as being a significant driver of microbial succession. Microbial co-occurrence network analysis highlighted close bacterial-fungal interactions. Compared with spontaneous fermentation, both inoculated systems reduce the content of off-flavor arginine and enrich glutamic acid as the dominant umami component. While co-inoculation of Pichia kudriavzevii increases acetic acid concentration, this yeast does not induce statistically significant changes to the overall sensory profile. This study provides a foundation for using microbial agents to optimize Allium chinense bulb fermentation and standardize industrial production.