Immobilization of papaya laccase in chitosan led to improved multipronged stability and dye discoloration.

A purified papaya laccase was immobilized in chitosan beads using entrapment approach and its physico-chemical properties were investigated and compared with that of free enzyme. Increase in properties of the laccase such as optimum temperature (by 10 °C), thermostability (by 3-folds) and optimum pH (from 8.0 to 10.0) was observed after immobilization. Immobilization led to increased tolerance of enzyme to a number of metal ions (including heavy metals) and organic solvents namely, ethanol, isopropanol, methanol, benzene and DMF. The catalytic efficiency (Kcat/Km) of the immobilized enzyme was found to increase more than ten folds, in comparison to that of the free enzyme, with hydroquinone as substrate. Immobilization of laccase also led to improvement in dye decolorization such that the synthetic dye indigo carmine (50 μg/ml) was completely decolorized within 8h of incubation as compared to that of the free laccase which decolorized the same dye to only 56% under similar conditions. Thus, immobilization of laccase into chitosan beads led to tremendous improvement in various useful attributes of this enzyme thereby making it more versatile for its industrial exploitation.