Magnetized polysiloxane coated with polyaniline (mPOS-PANI) was used as a support for beta-galactosidase immobilization via glutaraldehyde. The galactooligosaccharides (GOS) production by this derivative was investigated under different initial lactose concentrations (5-50%) and temperatures (30-60 degrees C). The initial lactose concentration in the reaction media affected the total amounts of produced GOS and their time course production was described as a "bell-shaped" curve as a result of the balance between trans-galactosylation and hydrolysis. No significative difference was observed for the free and immobilized enzymes. The reaction rates for lactose hydrolysis and GGS formation increased with increasing temperature from 30 degrees C to 60 degrees C, but GOS production at all lactose conversion levels was almost unchanged with changing temperature. The mPOS-PANI matrix was also characterized by scanning electronic microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), thermomagnetization, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). (C) 2009 Elsevier Ltd. All rights reserved.