Development a modified MRS medium for enhanced growth of psychrotrophic lactic acid bacteria isolated from kimchi

When culturing psychrotrophic lactic acid bacteria (LAB) isolated from kimchi, the commonly used de Man, Rogosa and Sharpe (MRS) medium does not sufficiently satisfy the nutritional requirements for all bacteria. To overcome this limitation, a modified MRS medium (m-MRS) and culture conditions tailored for psychrotrophic LAB were developed via statistical optimization using response surface methodology (RSM) and partial least squares-genetic algorithm (PLS-GA). A one-factor method based on the MRS medium was used to determine the medium composition. Glucose, sucrose, and mannose (6.7 g/L each) were selected as carbon sources, and soy peptone (19.11 g/L), a plant-based alternative, was used as a nitrogen source, replacing beef extract. Tomato juice (1 g/L) and L-ascorbic acid (0.1 g/L) were selected as growth factors. These factors were treated as independent variables and optimized using RSM, and PLS-GA. Temperature, incubation time, and pH were utilized as independent variables for RSM and PLS-GA to optimize the culture conditions. Compared to the MRS medium, the m-MRS broth provided better support for the growth of most psychrotrophic LAB strains tested. Thus, m-MRS medium and optimized conditions can be effectively applied to culture psychrotrophic LAB isolated from kimchi.