BACKGROUND Aspergillus oryzae beta-galactosidase (beta-gal; EC 3.2.1.23) was physically adsorbed on polyaniline-chitosan nanocomposite (PANI-CS-NC) and polyaniline-chitosan-silver nanocomposite (PANI-CS-Ag-NC). Stability and kinetic studies were assessed, along with reusability and molecular docking interactions. RESULTS According to transmission electron microscopy images, the sizes of the respective NCs were found to be in the range of 23-39 and 6-18 nm. The eta (effectiveness factor) values for PANI-CS-NC- and PANI-CS-Ag-NC-bound beta-gal were calculated to be 0.89 and 1.23, respectively, suggesting an enhancement in the activity of the enzyme in the presence of silver ions. Significant broadening was observed in pH and temperature profiles. Kinetic properties of PANI-CS-NC- and PANI-CS-Ag-NC-bound beta-gal showed lower K-m, and two- and fourfold higher V-max, respectively, compared to free enzyme. PANI-CS-Ag-NC-bound beta-gal was able to retain 94% of its initial activity after 10 repeated uses. Circular dichroism analysis revealed conformational changes in the secondary structure of protein upon immobilization. The genotoxic assessment revealed non-toxic behaviour of both free and enzyme-bound NC. The rate of lactose hydrolysis at 50 degrees C exhibited by PANI-CS--Ag-NC bound beta-gal was 7% higher than that for the native enzyme. In-silico analysis showed efficient binding of beta-gal on PANI-CS- NCs due to interaction with residues that were exclusive of the active site of the enzyme. CONCLUSION PANI-CS-Ag-NC-bound beta-gal preparation proved to be a robust nano-biocatalyst due to remarkable enhancement in catalytic activity along with excellent stability and reusability characteristics, which could be further utilized for efficient construction of nano-biosensors for producing lactose-free dairy products to feed lactose-intolerant patients. (c) 2018 Society of Chemical Industry