Exploratory and Targeted Metabolomic Characterization of a Fermented Soy Postbiotic Highlights Compositional Signatures Potentially Relevant to Gastric Comfort

Background/Objectives: Fermentation is recognized for improving the nutritional content and health benefits of soy products. Gastro-AD® (GAD) is a postbiotic ingredient produced from soy flour by controlled fermentation with a proprietary strain Lactobacillus delbrueckii subsp. lactis R0187. GAD has been reported to exert beneficial effects against gastric discomfort (heartburn, acid reflux) in recent studies and to support gastric ulcer healing or prevention in early clinical and preclinical studies. However, the metabolite composition of GAD and the molecular pathways potentially relevant to its reported effects remain incompletely characterized. Methods: To complement our previous compositional analysis by 1H-NMR, exploratory capillary electrophoresis–Fourier transform mass spectrometry was used to compare polar metabolite features in GAD and its unfermented soy starting material. Features were prioritized using a GAD relative peak-intensity cutoff of 0.01 and a GAD-to-soy fold-change cutoff of 2. Targeted quantitative metabolomics was subsequently used to evaluate amino acids and organic acids across six independent GAD production lots and their corresponding unfermented soy controls. Results: Among the 116 non-duplicate features included in the biochemical category analysis, amino acids and derivatives represented the largest category by feature count. Targeted analysis confirmed reproducible differences in the amino acid and organic acid profiles across six matched GAD and unfermented soy materials. Of 22 quantified amino acids and derivatives, 18 met the FDR criterion, while 13 of 19 fully quantified organic acids met the FDR criterion. Most quantified amino acids were higher in GAD, while the organic acid profile showed selective increases and decreases consistent with extensive metabolic transformation during fermentation. Integration with the published literature identified gastrointestinal nutrient sensing, mucosal responses, cellular stress resilience, and redox-related metabolism as hypotheses for future functional investigation. Conclusions: Exploratory profiling followed by targeted quantitative analysis identified a reproducible fermentation-associated metabolite signature in GAD. The findings provide a compositional framework for investigating pathways potentially relevant to gastric comfort.