Physicochemical properties and differential metabolites associated with mustard fermentation by Pediococcus...

Fermented vegetable foods, with their crisp taste, pleasant aroma, and digestive properties, are increasingly popular. This study investigated improved safety and quality of fermented mustard products, using two strains of lactic acid bacteria, Pediococcus pentosaceus M52 and Lactiplantibacillus pentosus H1, isolated from traditional naturally fermented sauerkraut from Nanning, Guangxi Zhuang Autonomous Region, China. The effects of co-inoculation of the two strains on the physicochemical properties of the food were assessed by measuring the levels of indicators such as lactic acid, glucose and nitrite. The results showed that the optimum ratio of inoculation of Pediococcus pentosaceus M52 and Lactiplantibacillus pentosus H1 was 2:1 at 1% inoculation, and the physicochemical indicators of the co-inoculated fermented mustard were improved relative to naturally or single strain- inoculated fermented mustard. Non-targeted metabolomics was used to analyze and compare metabolites between naturally fermented and co-inoculated fermented mustard. The largest proportion of metabolites found was carboxylic acid and their derivatives (16.46%), while the second-largest proportion was undefined (11.91%). A total of 206 significant differential metabolites were identified, of which 139 were identified in the cationic mode and 67 in the anionic mode. Among them, amino acid, peptides and peptides analogs, carbohydrates and carbohydrate conjugates, and benzene and substituted derivatives, showed greatest diversity. The significantly up-regulated differential metabolites in co-inoculated fermented mustard included amino acid, organic acid and derivatives, heterocyclic and benzene ring- containing compounds. Improved flavor and nutritional value of the fermented mustard were associated with increased amino acid, organic acid, and aromatic substance levels. Functional analyses showed enrichment of the differential metabolites in various metabolic pathways, involved in ABC transporters, galactose metabolism, phosphotransferase system, biosynthesis of amino acid, nucleotide metabolism, biosynthesis of secondary metabolites and other metabolic pathways. Moreover, nutrients such as vitamin C, adenosine 3'-monophosphate and trans-ferulic acid were significantly increased. These findings clarify the differences in physicochemical properties and metabolic characteristics between naturally fermented and co-inoculated lactic acid bacteria-fermented mustard, providing a reference for the standardized and large-scale production of co-inoculated lactic acid bacteria- fermented vegetables.