Temperature shift and feeding strategies for improving L-lactic acid production by Lactiplantibacillus plantarum in batch and fed-batch cultures

The optimal culture conditions for L-lactic acid production by Lactiplantibacillus plantarum TBRC 9667 were investigated. The suboptimal initial pH and initial temperature (for upshift to 30 degrees C after 5 h) were first determined in shake-flask cultures to be pH 5.5 and 25 degrees C, respectively. The three process variables analysis (initial temperature of 25 degrees C or 30 degrees C, temperature upshift to 30 degrees C or 35 degrees C, and temperature shift point at 3 or 5 h) revealed a 25 degrees C - 35 degrees C temperature shift after 3 h to be the most suitable conditions for L-lactic acid production in batch cultures at controlled pH 5.5. Fed-batch experiments were further conducted in 2-L bioreactors using different glucose concentrations (20 and 40 g/L) and feed rates (calculated with a feed-rate equation based on an off-line Markov chain algorithm), with an initial feed rate of 0.3 L/h. A 25 degrees C - 35 degrees C temperature shift after 3 h, with 20 g/L glucose feeding after 9 h using an exponent of 0.025 for feed-rate, gave a 1.5-fold improvement over the suboptimal batch culture. The results highlight the potential of integrated temperature shift and off-line feeding strategies for improving L-lactic acid production.