Some biochemical properties of polyphenol oxidase from two varieties of avocado

A study of crude polyphenol oxidases from two avocado (Persea americana Mill.) varieties, Booth 1 (b1PPO) and Julio Millán (jmPPO), were carried out to provide information useful for guiding food processing operations. Results are reported as “apparent” data because crude extracts were used, activities of which can be derived from a combination of isoenzymes. The pH-activity optimum was pH 7.5–7.6 for both extracts. Heat inactivation, between 67 and 84 °C was biphasic with activation energies ranging from 21.4 to 64.1 kcal/mol. The apparent substrate specificity was established from values Vmax/Km as: 4-methyl catechol>chlorogenic acid>pyrogallol>catechol>caffeic acid>dl-DOPA for b1PPO. The substrate specificity for jmPPO was: 4-methyl catechol>chlorogenic acid>pyrogallol>caffeic acid>catechol>dl-DOPA>protocatechuic acid. The order of inhibitor effectiveness was: l-cysteine>ascorbic acid>resorcinol>glycine>NaCl.