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 degrees C for SEPPO and 39.4 degrees C 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 degrees C by 5 min, SUPPO was denatured whereas SEPPO retained 2.6% of activity. Activation enthalpy (Delta H-#) and activation entropy (Delta S-#) for SEPPO heat-inactivation were 69.9 J/mol and -83.5 kJ/mol.K for SUPPO, Delta H-# was 91.8 J/mol while Delta S-# was -21.0 kJ/mol. K. Substrate specificity (V-max/K-M) was 4-methylcatechol>catechol>pyrogallol for SEPPO and 4-mehtylcatechol>pyrogallol>catechol for SUPPO. For both enzymes, the order of inhibition effectiveness using reductor agents was metabisulphite>ascorbic acid. Benzaldehyde, 4-hydroxybenzaldehyde, and DL-dopa were competitive inhibitors, and their K-1 values were 38.86, 8.43, and 2.08 mM, respectively.