LACTIC ACID PRODUCTION BY MUTAGENIZED ENTEROBACTER HORMAECHEI SUBSP. XIANGFANGENSIS ISOLATED FROM PROCESSED MILK

Lactic acid (LA), a valuable weak natural organic acid extensively utilized in various industries has been conventionally synthesized through chemical processes. However, the growing demand for sustainable and eco-friendly production methods has stimulated interest in microbial synthesis. The study was to explore the potential of multi-strain lactic acid bacteria isolated from processed liquid milk to synthesize lactic acid. Microorganisms were isolated and screened on deMan Rogosa Sharpe (MRS) agar and were identified according to morphological and biochemical characteristics. Mutagenesis of positive isolate using chemical and physical means, quantitative and qualitative production using High-Performance Liquid Chromatography (HPLC) were investigated. The isolate was discovered to have a clear zone on MRS agar, which allowed for its molecular characterization as Enterobacter hormaechei subsp. xiangfangensis It was then chosen for mutagenesis using ethidium bromide (EB) and UV light. Thirteen mutants were identified, and three of those were examined to see if they could generate LA using various substrates. HPLC confirmed mutants and parent strain to produce hetero-fermentative lactic acid using cheese whey substrate. The UV mutant strain showed a significantly higher yield (2008.50 µg/mL) than both the EB mutant (1451.25 µg/mL) and the parent strain (233.75 µg/mL) at 37 °C, pH 4.5, and 150 rpm 16 h fermentation period. This study showed that mutagenesis greatly influences optimum LA production due to mutants developing enhanced cell membrane integrity and pH tolerance, thus permitting strains to synthesize LA even at inhibitory concentrations.