A Modelling study on skimmed milk lactose hydrolysis and [beta]-galactosidase stability using three reactor types

The hydrolysis of lactose in skimmed milk and [beta]-galactosidase inactivation studies were carried out in three different devices - bioreactor, sonicator and homogeniser - to evaluate the performance of such reactors that have different operational systems. The experiments were carried out using [beta]-galactosidase produced from Kluyveromyces marxianus lactis. At the optimum process conditions obtained from the experiments performed in bioreactor, sonicator and homogeniser, 89%, 90% and 54% of lactose were hydrolysed and the enzyme lost its activity by 14%, 13% and 24%, respectively, at the end of the processing time of 30min. The commercial milk lactose content (1g/L lactose) was reached at 60min for bioreactor and sonicator. After evaluation of the data, it was found that the kinetics of hydrolysis and enzyme inactivation could be represented by a first-order kinetic model and a single-step non-first-order enzyme inactivation kinetic model, respectively, for all process conditions applied. The activation energy for hydrolysis reaction and the enzymatic inactivation energy values were also calculated. [PUBLICATION ABSTRACT]