Kinetic Modeling of Lactose Hydrolysis in Cow’s Milk by Aspergillus oryzae β-Galactosidase: Parameters for the Design of an Enzymatic Reactor

Lactose intolerance is a common limitation to the consumption of cow’s milk in humans, and insufficient consumption of this food has been associated with gastrointestinal disorders, osteoporosis, and nutritional deficiencies. Currently, different methods are available for lactose removal from milk, such as nanofiltration and ultrafiltration; however, these methodologies are associated with high costs. The objective of this study was to characterize the kinetics of lactose hydrolysis in cow’s milk using free β-galactosidase from Aspergillus oryzae. Lactose hydrolysis was performed at 40 °C and pH 6.6 using an enzyme concentration of 60 ALU/mL. The concentrations of the substrate (lactose) and hydrolysis products (glucose and galactose) were quantified by high-performance liquid chromatography (HPLC) over a reaction time of 0–200 min. The kinetics were evaluated using the Michaelis–Menten model and the following inhibition models: (I) competitive, (II) uncompetitive, and (III) non-competitive inhibition. Lactose concentration decreased from 48 to 4.30 mg/mL, corresponding to 91.05% hydrolysis, while glucose increased from 4.01 to 12.07 mg/mL and galactose increased from 0.36 to 19.53 mg/mL. The estimated kinetic parameters were Vmax = 3.09 mg/(mL·min) and Km = 40.33 mg/mL. The uncompetitive inhibition model provided the best fit for glucose, with a root mean square error (RMSE) of 0.0553, a sum of squared errors (SSE) of 0.0275, and a coefficient of determination (R2) of 0.9555.