Use of novel immobilized β‐galactosidase reactor to hydrolyze the lactose constituent of skim milk

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Abstract
β-galactosidase from Aspergillus oryzae immobilized in an axial-annular flow reactor was used to effect the hydrolysis of the lactose component of skim milk. Nonlinear regression methods were employed to determine the kinetic parameters of four rate expressions derived from a proposed enzymatic mechanism. Data taken at three different temperatures (30°C, 40°C, and 50°C) were fit via nonlinear regression methods assuming an Arrhenius temperature model for each of the parameters. For the reaction conditions used in this research, a three-parameter rate expression which includes the separate competitive inhibition effects of α- and β-galactose (and the associated mutarotation reaction) is sufficient to model the hydrolysis of lactose in skim milk. The effects of temperature on the individual kinetic parameters are small. The most significant effect appears in the term for inhibition by the β anomer of galactose (EA = 10.3 kcal/mol). At 40°C and a space time of 10 min, 70% of the lactose present in skim milk can be hydrolyzed with the axial-annular flow reactor. This reactor can be used to hydrolyze the lactose in skim milk without the problems observed with other reactor configurations, namely, plugging due to particulates, microbial contamination, and large pressure drop.