Optimizing the growth-associated β-galactosidase production by probiotic <i>Lactobacillus reuteri</i> B-14171: experimental design, culture medium volume increase, and cell growth modeling

This study reports an optimized culture medium in submerged cultivation to produce β-galactosidase by Lactobacillus reuteri. Four culture medium parameters were optimized (pH, lactose, casein, and inactive beer yeast), and the effect of different volumes of the optimized culture medium on the bioprocess was evaluated regarding β-galactosidase production. Different kinetic models were applied to predict enzymatic production as a function of biomass and substrate. It is the first time that both the effect of increasing the culture medium volume and mathematical modeling on the β-galactosidase production by L. reuteri have been studied. Besides, different bioprocess parameters were calculated based on the experimental data to verify the feasibility of enzymatic production. The achieved enzymatic activity for the optimized culture medium (12.75 g L-1 lactose; 1.88 g L-1 casein; 1.65 g L-1 inactive beer yeast and pH 5.61) resulted in an increase of 4.74-fold compared to the initial activity. Three culture medium volumes (200, 800, and 3,200 mL) were evaluated, and no significant difference was observed on maximum and total productivities (Pm and Pp), as well as on the product formation yield on biomass (YP/X). The Logistic model resulted in a good fit to the experimental data for all tested volumes, and the modified Luedeking-Piret model provided a satisfactory prediction of the enzymatic activity. The optimized culture medium reported in this work is an outstanding alternative to produce β-galactosidase by L. reuteri, which is microbial growth-associated, and the production was not affected by increasing the culture medium volume.