Kinetic and metabolomic characterization of acid profile remodeling in sea buckthorn juice during mixed culture lactic acid bacterial fermentation.

Sea buckthorn juice has a sharp acidic taste due to its high organic acid content, and its fermentation process is complex. In this study, two acid and bile-salt tolerant lactic acid bacterial strains, Lactiplantibacillus plantarum CICC 20999 and Streptococcus thermophilus CICC 6063, were screened. Among the tested inoculation ratios, the 1:1 mixed culture showed the highest deacidification performance, with an observed rate 13.1% higher than the monoculture based additive expectation. Response surface optimization identified 7% inoculum, 28 °C, and 25 h as the optimized fermentation conditions. Under these conditions, time course analysis showed that malic acid degradation reached 83.6%, while lactic acid increased to 11.91 mg/mL. The empirical kinetic models fitted the observed time course profiles of combined viable counts, total sugar, malic acid, and lactic acid under the tested conditions. Untargeted metabolomics further showed distinct differences in the nonvolatile metabolite profiles of SBJ and FSBJ, mainly involving organic acids, peptide related features, lipid related compounds, and amino acid related metabolites. KEGG assisted pathway mapping organized representative DEMs into modules comprising amino acid related metabolites, central carbon and organic acid related metabolites, and metabolites assigned to transport related pathways. These pathway assignments provided an annotation level framework for the observed metabolite changes. Together, kinetic modeling and metabolomics provided complementary process level and metabolite level descriptions of mixed culture fermentation and offered a methodological reference for quality regulation of highly acidic plant based beverages.