CONTINUOUS SPECTROPHOTOMETRIC METHOD FOR DETERMINING MONOPHENOLASE AND DIPHENOLASE ACTIVITIES OF PEAR POLYPHENOLOXIDASE

A continuous spectrophotometric method was based on the coupling react ion between 3-methyl-2-benzothiazolinone hydrazone (MBTH) and the quin one product of the oxidation of p-hydroxyphenyl propionic acid (PHPPA) or 3,4-dihydroxyphenyl propionic acid (DHPPA) in the presence of poly phenol oxidase. The monophenolase activity of pear PPO was characteriz ed for the first time. Solubility and stability of the adduct formed a t the optimum pH (4.3) enabled the system to reach steady-state, makin g it possible to determine monophenolase activity with short lag perio ds. This, together with the value of epsilon for the MBTH-quinone addu ct, makes this method more sensitive than other continuous methods for assaying monophenolase and diphenolase activities.