Characterization of Polyphenoloxidase from 2 Peach (Prunus persica L.) Varieties Grown in Argentina

Polyphenoloxidase was extracted from September peach (∧SEPPO) and Summerset peach (∧SUPPO) and its physicochemical characteristics were analyzed. The optimum pH was 6.5 for ∧SEPPO and 5.5 for ∧SUPPO. The optimum temperature was 35℃ for ∧SEPPO and 39.4℃ for ∧SUPPO. Activation energy (Ea) from thermal activation was 41.5 kJ/mol for ∧SEPPO and 37.5 kJ/mol for ∧SUPPO. Heating at 60℃ by 5 min, ∧SUPPO was denatured whereas ∧SEPPO retained 2.6% of activity. Activation enthalpy (ΔH∨No.) and activation entropy (ΔS∨No.) for ∧SEPPO heat-inactivation were 69.9 J/mol and -83.5 kJ/molㆍK for SUPPO, Delta H∨No. was 91.8 J/mol while ΔS∨No. was -21.0 kJ/molㆍK. Substrate specificity (V∧max/K∧M) was 4-methylcatechol greater than catechol greater than pyrogallol for ∧SEPPO and 4-mehtylcatechol greater than pyrogallol greater than catechol for ∧SUPPO. For both enzymes, the order of inhibition effectiveness using reductor agents was metabisulphite greater than ascorbic acid. Benzaldehyde, 4-hydroxybenzaldehyde, and DL-dopa were competitive inhibitors, and their K∧I values were 38.86, 8.43, and 2.08 mM, respectively.