Electrochemical Measurement of Immobilized Onion Leaves PPO in Agar-Abelmoschus Escucentus Gum

Onion leaves monophenol monooxygenase and o-diphenol oxidase were extracted by salt and solvent method followed by purification on affinity column using natural affiant. For the fabrication of enzyme-based biosensor, composite matrix of natural biopolymers agar-Abelmoschus escucentus gum was used to immobilize monophenol monooxygenase and o-diphenol oxidase. L-tyrosine and L-dopa were used as substrate for the measurement of phenol. Monophenol monooxygenase and o-diphenol oxidase oxidizes phenolic substrate to the corresponding quinone to allow convenient low-potential detection of phenolic analyte. In the enzymatic catalysis, reduction of quinone to phenol was also observed using (vs.Ag/AgCl) at a platinum electrode. The Vmax for tyrosine and dopa is 102.4 and 108.2 μM/litre/min where as Km is 11.26 X 10-3 mM and 11.90 X 10-3 mM respectively. The biosensor exhibited good performance in terms of reusability, linearity, sensitivity, fabrication, simplicity, shelf-life and operational stability. Thus, the biosensor is suitable for the analytical quantification of phenols.