Evaluation of two polyphenoloxidase kinetic parameters at three stages of <i>Musa sapietum</i> fruit maturation

Abstract

The activity of polyphenoloxidase extracted from Musa sapietum fruit was investigated at three stages of the fruit maturation; the developmental, matured and ripened stages of the fruit. Spectrophotometric method was used to assay for the enzyme activity and two enzyme kinetic constants, maximum enzyme activity (Vmax) and Michealis–Menten constant (Km) were evaluated. The values of Vmax were 3.33 x 10 -4, 4.00 x 10 -4 and 9.09 x 10 -4 O.D/Sec at the developmental, matured and ripened stages respectively. The Michealis – Menten constant (Km) was the same during the three stages of maturation with values standing at 2.5 x 10 -3 M. The difference in the values of Vmax was a reflection of variations in the absolute quantity of polyphenoloxidase and probably, the concentration of polyphenolic compounds present at the three stages of fruit maturation. Furthermore, the observed Km value was an indication that the physicochemical properties of the enzyme at the three stages were identical and did not vary.


Keywords: Banana, Musa Sapietum, Polyphenoloxidase, Michealis–Menten constant, enzyme activity

IJOTAFS Vol. 1 (1) 2007: pp. 63-67