Optimization of cultivation conditions for Lactobacillus acidophilus to produce lactic acid through molasses fermentation

Lactic acid and its salts (lactates) are used extensively in the food industry as acidity regulators and as raw materials for the synthesis of polylactide, a biodegradable packaging material. Currently, the prevailing method of producing lactic acid involves the biosynthetic pathway, using sugar-containing raw materials such as beet molasses. This study aims to examine the process of molasses bioconversion into lactic acid using the anaerobic strain Lactobacillus acidophilus AT-I. The concentrations of carbon (molasses) and nitrogen (yeast extract) were optimized using a central composite design experiment. The lactic acid content in the culture liquid was analyzed using capillary electrophoresis. The model was constructed in the R environment, and its adequacy was assessed using Fisher’s F-test. The findings demonstrated that the model adequately described the experimental data at a significance level of 0.05 (the variance of adequacy of the regression equation of 0.28, R² = 0.76, the calculated value of the F-criterion (3.2) is less than the tabulated value (6.3)). According to the model, the highest conversion of molasses to lactate (5.6%) should be observed at a molasses concentration of 63 g/L and a yeast extract concentration of 1.9 g/L. The cultivation of Lactobacillus acidophilus AT-I in a bioreactor exhibited classical kinetics of carbohydrate breakdown and lactic acid accumulation, with lactic acid content reaching 5.5 g/L after 96 hours.

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