Modeling of the simultaneous hydrolysis–ultrafiltration of whey permeate by a thermostable β-galactosidase from Aspergillus niger

Abstract

A wild type strain of Aspergillus niger, denoted as BTL, produced elevated levels of β-galactosidase when grown in a low cost medium that contained wheat bran as the sole carbon and energy source. The enzyme was collected, concentrated and partially purified from the culture supernatant. Its kinetic and stability properties were thoroughly examined towards its potential use for the hydrolysis of acid whey permeate lactose. The β-galactosidase of A. niger BTL showed increased pH and thermal stability, with activation energy for the first order deactivation constant equal to 180 kJ/mol at pH 3.5. Lactose hydrolysis by the enzyme was described by Michaelis–Menten kinetics with competitive inhibition only from galactose. An integrated process, concerning the simultaneous hydrolysis–ultrafiltration of whey lactose that incorporated the specific kinetic properties of the β-galactosidase was developed and modeled. The model proved very successful in predicting the behavior of a continuous laboratory hydrolysis–ultrafiltration set up, specifically designed for that purpose. The validated model was finally used in a number of computer simulations in order to investigate the effect of the various process parameters on the overall system performance.