Production of Lactic Acid Using a Co-culture of Lactobacillus paracasei and Levilactobacillus brevis

Lactic acid bacteria (LAB) are the most important bacteria in desirable food fermentations, being responsible for the fermentation of sourdough bread, fermented foods and beverages, all fermented milks and fermented vegetables. They play essential roles in the production of all dairy products and is involved in the production of many other fermented foods and beverages, sausages, pickles, etc. This study aimed to produce lactic acid using lactic acid bacteria isolated from pap “akamu” and liquid milk samples. The following procedures were conducted to achieve the objectives of the study, which include sample collection, isolation of lactic acid bacteria (LAB) from samples, screening of LAB for lactic acid production, characterisation of selected lactic acid bacteria, and optimisation of process parameters for lactic acid production. Results from the study showed that the highest lactic acid production (6.39 mg/ml) from milk samples was observed from an isolate from milk sample 2, while for the pap samples, the highest lactic acid production (2.79 mg/ml) was observed from an isolate from pap sample 4. The highest lactic acid producers from the milk and pap samples were identified based on their macroscopic, microscopic and molecular characteristics. The bacteria were identified as Lactobacillus paracasei (sample milk 2) and Levilactobacillus brevis (sample pap 4). Biochemical characterisation indicated the metabolic capabilities of these isolates, including acidifying properties, enzyme production, and fermentation abilities. The highest production of lactic acid by co-cultures of Lactobacillus paracasei and Levilactobacillus brevis was observed after 96 h of incubation. Enhanced lactic acid yield by the co-cultures was observed at pH 5.5 (8.6 mg/ml), while the lactic acid production decreased at a higher pH. The lactic acid concentration increased to the optimum lactic acid value (8.60 mg/mL) at 35°C, then decreased at 45°C. Maximum lactic acid production of 11.2mg/ml was observed at 200 rpm, the least of 4.9 mg/ ml was observed at zero or no agitation. The lactic acid production increased gradually with increasing inoculum size up to the maximum value (10.7 mg/mL) at 5% inoculum size. Lactic acid actually had the highest peak area, retention time and concentration in the GCFID chromatogram, while the other components had low values, further revealing the successful extraction of the lactic compound. The results of the present study indicated that the co-cultures of Lactobacillus paracasei (milk 2) and Levilactobacillus brevis (pap 4) isolated from milk and akamu, respectively, hold significant potential for lactic acid production.