Glucose-Dependent growth and antioxidant responses of lactic acid bacteria revealed by multivariate and Assay-Specific analyses.

Lactic acid bacteria (LAB) are valued in fermented foods for their health-promoting properties, including antioxidant activity that enhances product stability and nutritional value. Their antioxidant potential depends on strain type and culture conditions, with carbon source concentration playing a critical role. This study examined how glucose concentration influences LAB growth and antioxidant activity. Six strains isolated from traditional fermented seafood were cultivated in modified MRS media (0-10 g/L glucose) and standard MRS broth. Growth (pH, viable cell counts) and antioxidant activity (DPPH, ABTS, CUPRAC assays) were assessed. Moderate glucose levels (2-6 g/L) supported robust growth (> 8 log CFU/mL). In contrast, excessive glucose inhibited proliferation due to osmotic stress and metabolite accumulation. pH decreased with increasing glucose, with stronger acidification at higher levels. Antioxidant responses were assay-dependent: DPPH peaked at moderate glucose, ABTS showed a U-shaped trend influenced by acidification, and CUPRAC increased linearly. To clarify these patterns, regression modeling, correlation analysis, and principal component analysis (PCA) were applied. DPPH, ABTS, and CUPRAC followed quadratic trends, with explanatory power improved after covariate adjustment for pH. Correlation and PCA confirmed that pH was a major confounding factor, separating reducing power (DPPH, CUPRAC) from acidity-dependent activity (ABTS, pH). These findings highlight that antioxidant capacity cannot be interpreted from a single assay alone and that assay-specific and pH-dependent effects must be considered. Optimizing carbon source concentration offers a practical approach to balance LAB growth with antioxidant potential, supporting the development of functional fermented products with tailored bioactive profiles.