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 safe source of β-galactosidase was investigated. Three different bulk starter media with different compositions were selected, and an industrial yogurt starter culture strain, L. bulgaricus DSM 20081 was cultivated in these media under pH-controlled conditions (pH=5.6) at 43°C. The media consisted of 1) bulk starter medium based on skim milk and whey, 2) bulk starter medium based on whey, and 3) reconstituted skim milk. The kinetic parameters of growth and β-lactic acid production were estimated using the experimental data with the Garcia and Luedeking-Piret models, respectively. β-galactosidase production kinetics was also simulated using appropriate models based on biomass and lactic acid production. Growth in the bulk starter medium based on skim milk and 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 other two media (Plt 0.01). Simulation of β-galactosidase production based on the rate of lactic acid production resulted in a very good agreement with the experimental data of 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.