Boosting Probiotic Biomass of Lactobacillus acidophilus CCFM137 Through pH-Stat Morphological Control and Medium Optimization

The fermentation performance of Lactobacillus acidophilus is constrained by factors such as low cell density and fastidious nutritional and environmental requirements, which greatly limit its industrial-scale applications. This study aimed to develop an efficient fermentation condition for L. acidophilus CCFM137 through systematic optimization of both culture medium and environmental parameters, thereby enabling high-yield industrial-scale production of this strain. An optimized medium was developed, consisting of glucose (30 g/L), YEP FM503 (35 g/L), sodium acetate (5 g/L), ammonium citrate (2 g/L), K2HPO4 (2 g/L), MgSO4·7H2O (0.1 g/L), MnSO4·H2O (0.05 g/L), L-cysteine hydrochloride (0.5 g/L), and Tween 80 (1 mL/L), to achieve a viable cell count of 1.95 × 109 CFU/mL, representing a 9.42-fold increase over that of standard MRS broth. Subsequent pH-stat fermentation trials in a 100 L fermenter using the optimized medium revealed morphological and growth characteristics of the strain in variable pH-stat environments. Optimal performance was observed under pH-stat 4.5 rather than the more commonly used 5.7, achieving maximum viable cell counts of 3.37 × 109 CFU/mL, accompanied by a transformation of cell morphology toward shorter rod-shaped structures, as well as an increase in substrate utilization rate, cell recovery rate and lyophilization survival rate. The fermentation performance and cellular morphology of L. acidophilus CCFM137 were enhanced by both nutrient composition and pH environment. These results showed that this strategy has potential for application in high cell density fermentation of L. acidophilus CCFM137.