Kinetics of β-galactosidase Production by Lactobacillus bulgaricus During pH Controlled Batch Fermentation in Three Commercial Bulk Starter Media

The potential of bulk starter fermentation strategy for production of a cost-effective and GRAS source of β-galactosidase from a starter culture strain Lactobacillus bulgaricus was investigated. Three different media were selected and the strain, L. bulgaricus DSM 20081 was cultivated in these media under pH-controlled condition (pH = 5.6) at 43°C. The media were: bulk starter medium based on skim milk + whey, bulk starter medium based on whey, and skim milk. Growth and β-lactic acid production parameters were estimated from experimental data with the Garcia and Luedeking-Piret models, respectively. β-galactosidase production kinetics was also simulated using models based on biomass concentration and lactic acid production. Growth in the bulk starter medium based on skim milk + whey resulted in a higher rate of lactic acid production (7.35 ± 0.23 mg lactic acid ml-1 media h-1) and β-galactosidase activity (800.1± 0.7 nmol ONP ml-1 media) compared to the other two media (P<0.01). Simulation of β- galactosidase production based on rate of lactic acid production resulted in very good agreement with experimental data for all three tested media. The results revealed the potential of bulk starter fermentation strategy and skim milk + whey based medium for in-house and relatively low cost production of food-grade β-galactosidase by dairy plants.