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

Abstract

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 °C after 5 h) were first determined in shake-flask cultures to be pH 5.5 and 25 °C, respectively. The three process variables analysis (initial temperature of 25 °C or 30 °C, temperature upshift to 30 °C or 35 °C, and temperature shift point at 3 or 5 h) revealed a 25 °C – 35 °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 °C – 35 °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.