Effect of metal ions present in milk on the structure and functional integrity of native and polyaniline chitosan nanocomposites bound β-galactosidase: A multi-spectroscopic approach

beta-Galactosidase is vital to dairy industries because it catalyzes the hydrolysis of lactose into glucose and galactose making it useful for lactose intolerant patients to consume milk and its products. The present study demonstrates the effect of metal ions commonly found in milk, namely Zn2+, K+, Ca2+ and Mn2+ on the activity of native and polyaniline chitosan nanocomposites bound Aspergillus oryzae beta-galactosidase. In polyaniline chitosan silver nanocomposite adsorbed beta-galactosidase, a multi-fold enhancement in catalytic activity was observed in the presence of cocktail of Zn2+, K+, Ca2+ and Mn2+ ions. 3D fluorescence, CD and FTIR studies established significant conformational changes in the secondary structure of polyaniline chitosan silver nanocomposite bound beta-galactosidase on addition of metal ions as compared to the native and other bound enzyme. This enhanced catalytic efficiency of the immobilized enzyme in presence of metal ions can promote its economic use for lactose hydrolysis in milk.