CHARACTERIZATION AND INHIBITION OF POLYPHENOL OXIDASE FROM PEARS (PYRUS-COMMUNIS L CV BOSC AND RED)

Red pears had higher PPO activity, total phenolics and chlorogenic acid concentration than Bosc pears. PPO activity and phenolics both decreased in fruits held at room temperature. pH and temperature optima for Bosc and Red pears PPOs were 5.0 and 5.5, and 20 and 23C, respectively. 4-Methylcatechol, catechol and dopamine were good substrates for PPO from both pear cultivars; however, no activity was observed with any of the mono-hydroxy substrates studied. Higher K(m) and lower V(max) values were observed for Bosc pear PPO. Heating at 75C for 30 min completely inactivated the enzyme from both cultivars. Heating at 55 and 65C for the same duration resulted in partial inactivation (45-60%) of this enzyme. Ascorbic acid, L-cysteine, sodium metabisulfite and thiourea effectively inhibited browning due to pear PPOs.