Abstract: The demand for optically pure lactic acid (LA) is increasing due to its applications in the food, pharmaceutical, and biodegradable plastics industries. This study evaluated L-LA, D-LA, and DL-LA production using Lacticaseibacillus casei, L. coryniformis ATCC 25600, and Lactiplantibacillus plantarum, respectively, cultivated in laboratory-scale bioreactors with controlled pH and temperature. Agroindustrial byproducts, including sugarcane molasses, glucose-fructose syrup, and whey permeate, were compared with glucose as a reference substrate. Lacticaseibacillus casei reached the highest L-LA concentration in whey permeate (86?g L?1 in 24?h), with a yield of 1.07?g g?1 and maximum productivity of 4.70?g L?1 h?1, values higher than previously reported for lactose-based media. Lacticaseibacillus coryniformis ATCC 25600 achieved 70?g L?1 of D-LA from glucose-fructose syrup (95?g L?1 initial sugars) in 72?h, with complete sugar depletion, yield of 0.75?g g?1, and productivity of 1.95?g L?1 h?1. For DL-LA, L. plantarum produced 70?g L?1 in whey permeate within 48?h (87% sugar removal, yield 0.76?g g?1, productivity 1.44?g L-1 h?1). Across all strains, whey permeate and syrup enabled the most efficient fermentations, whereas molasses showed potential but was limited by nitrogen content. These results highlight the feasibility of valorizing low-cost byproducts for optically pure LA production and provide kinetic and stoichiometric benchmarks to guide industrial process design.

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