Untargeted metabolomics and physicochemical analyses reveal metabolic mechanisms underlying quality modification in sour porridge fermented with Lacticaseibacillus paracasei subsp. paracasei GXUN74722

Traditional fermented sour porridge is a characteristic traditional fermented food in Guangxi Zhuang Autonomous Region, China, featuring distinctive sensory flavor and abundant microbial diversity. In this study, a strain of Lacticaseibacillus paracasei subsp. paracasei GXUN74722 was isolated and identified from traditional fermented sour porridge collected from Fusui County, Chongzuo City, Guangxi Zhuang Autonomous Region, China. The strain exhibited high fermentation efficiency in sour porridge production. Using pH value and titratable acidity as core evaluation indices, the fermentation conditions for GXUN74722-inoculated sour porridge were systematically optimized. The optimal fermentation parameters were determined as follows: fermentation time of 72 h, inoculation dose of 12.5%, fermentation temperature of 37 °C, and glucose addition (2% glucose solution) at a volume fraction of 15%. Inoculated fermented sour porridge with strain GXUN74722 induced significant differences in the physicochemical characteristics and metabolic profiles of sour porridge relative to naturally fermented sour porridge. Untargeted metabolomics was applied to compare low-molecular-weight metabolite variations between naturally fermented and inoculated fermented sour porridge samples. Metabolomic analysis confirmed obvious discrepancies in metabolite composition between the two groups. Organic acids and their derivatives were the most predominant metabolites, accounting for 34.83% of the total identified metabolites, followed by organoheterocyclic compounds (17.53%), and lipids and lipid-like molecules (16.54%). A total of 1,312 metabolites were annotated in all samples, including 83 identified differential metabolites. These differential metabolites were primarily classified into amino acids, peptides and analogues, carbohydrates and carbohydrate conjugates, lipids and lipid-like molecules, as well as benzene and substituted derivatives. KEGG pathway enrichment analysis showed that five metabolic pathways were significantly altered, including ABC transporters, galactose metabolism, pentose phosphate pathway, carbohydrate digestion and absorption, and glycerophospholipid metabolism. Overall, inoculation with L. paracasei subsp. paracasei GXUN74722 reshaped the synthesis and accumulation profiles of metabolites in sour porridge. The observed physicochemical and metabolic shifts may underpin enhanced fermentation stability as well as modified sensory and nutritional attributes of fermented sour porridge. Since the present work only characterized physicochemical and metabolomic variations without dedicated sensory evaluation or in vivo functional tests, further validations are required to verify actual quality improvement and prospective health-promoting potentials of inoculated fermented sour porridge. These findings provide fundamental theoretical basis and technical references for the industrial development and standardized production of fermented sour porridge.