Revisiting lactic acid isomer production by lactic acid bacteria: Assessing process parameters and feedstock selection

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.