Comparative study of L/D lactic acid production in cultures of probiotic strains supplemented with carbohydrates from agave and other agroindustrial resources

The growth behavior and lactic acid production capacity including both L-lactic and D-lactic acid isomers of five probiotic strains ( Lactobacillus plantarum ATCC® 8014, L. rhamnosus ATCC® 53103, L. casei ATCC® 334, L. reuteri ATCC® 55730, and Bifidobacterium animalis ENCB-IPN) were systematically evaluated using defined carbon sources. Each strain was cultured for 24 h in modified MRS broth, where glucose was replaced with 1% (10 g/L) of individual substrates: monosaccharides (fructose, glycerol, rhamnose, arabinose, mannose, xylose, galactose), disaccharides (sucrose, cellobiose, lactose), a trisaccharide (raffinose), agave-derived fructooligosaccharides (FOS), and high-molecular-weight agave fructans (FAPM, DP > 10). Bacterial growth was monitored via optical density (OD595), and the specific growth rate ( μ ) and maximum OD were calculated. Fructose supported the highest total lactic acid production, particularly in L. plantarum and B. animalis , followed by sucrose, mannose, and cellobiose. Notably, L. rhamnosus achieved the highest L-lactic acid proportion (96%) with FAPM, while L. casei yielded 92.5% with cellobiose. In contrast, the highest D-lactic acid proportions were obtained with lactose (71.35% in L. plantarum , 55.88% in L. reuteri ) and with glycerol in L. casei (62%). Principal component analysis (PCA) showed limited correlation between growth and acid production when monosaccharides were used, but strong positive correlations were found with disaccharides and FOS, particularly between μ and lactic acid yield. This study highlights the relevance of using defined carbon sources to elucidate the substrate-specific metabolic behavior of probiotic strains. The results provide a comparative framework for selecting or engineering strains for targeted lactic acid production (including optical purity) and lay the foundation for future bioprocess optimization using complex substrates such as agro-industrial residues or functional oligosaccharides.