Chemical modification of laccase using phthalic and 2-octenyl succinic anhydrides: Enzyme characterization, stability, and its potential for clarification of cashew apple juice

The present study describes the chemical modification of laccase using succinic anhydride (SA) and two novel modifiers, viz. phthalic (PA) and 2-octenyl succinic (2-OSA) anhydrides. No change was observed in the optimum pH; however, a broadening of optimum temperature was observed for PA-laccase (30–70 °C) and 2-OSA-laccase (20–70 °C). The modified laccases displayed enhanced stability of 21% (SA-laccase), 42% (PA-laccase), and 29% (2-OSA-laccase) at pH 7 as compared to unmodified laccase. The effect of several surfactants, inhibitors, metal ions, and organic solvents at varying concentrations on the stability of modified laccases was evaluated. The modified laccases exhibited greater, though varying stabilities, than the unmodified laccase. The modifications significantly altered the intrinsic fluorescence but not the FTIR spectra and secondary structure of laccase. As a model example, cashew apple juice was clarified using modified laccases. There was a significant reduction in the polyphenol and condensed tannin content of the laccase-treated cashew apple juice. The polyphenol reduction was 29.33% (unmodified laccase), 33.09% (SA-laccase), 21.7% (PA-laccase), and 44.48% (2-OSA-laccase), while the condensed tannin reduction was 16.38% (unmodified laccase), 28.98% (SA-laccase), 28.1% (PA-laccase) and 28.59% (2-OSA-laccase). This is the first study on enzyme modification using OSA and clarifying cashew apple juice using laccase.