OPTIMIZED MEDIUM FORMULATION AND SCALE-UP FOR ENHANCED LACTIC ACID FERMENTATION FROM WHEAT STRAW HYDROLYSATE USING LACTIC ACID BACTERIA

The present study focuses on the scaling up of lactic acid production (LA) using renewable, undetoxified wheat straw hydrolysate. The latter was obtained by clean technologies based on dilute acid-catalyzed steam explosion coupled with enzymatic hydrolysis of polysaccharides to fermentable sugars (mainly glucose and xylose). Three Lactobacillus species (L. brevis ATCC 14869, L. plantarum ATCC 14917 and L. reuteri ATCC 23272) were evaluated to identify the most effective one and to optimize fermentation conditions. Initially, De Man-Rogosa-Sharpe (MRS) broth was blended with the sugar-rich hydrolysate (glucose 74.30 g/L, xylose 21.50 g/L) to execute dilution trials at different ratios. Preliminary trials in 15-mL tubes identified L. brevis as the most prolific LA producer. Further optimization revealed that a C/N ratio of 6 g/g significantly improved LA production to19.79 ± 1.51 g/L. Additionally, using yeast extract as a nitrogen source eliminated the need for hydrolysate dilution with MRS media. Subsequently, the process was scaled up to 100-mL Pyrex bottles under controlled conditions (pH 6, 37 °C, 200 rpm), with a 50% working volume proving optimal. This optimized process achieved a LA concentration of 42.55 ± 2.13 g/L within 72 hours, using CaCO3 for pH control during fermentation. This demonstrates the process efficacy and scalability on a complex substrate. The optimized process successfully enhanced LA titers and selectivity, thereby fostering sustainable LA production within modern biorefinery schemes.