Abstract:

With catechol as substrate, the change laws of reaction kinetics of apple polyphenol-oxidase (PPO) induced by alternating magnetic field were studied. The results indicated that the reaction kinetic of apple PPO browning is in accordance with Michaelis equation, and the Km and Vmax are 0.000687 mol/L and 0.0477 U/min, respectively. When the magnetic field strength is less than 0.87 A/m, the reaction system shows to be promoted; When the magnetic field strength is 1.67 A/m, the reaction system shows to be promoted by less 3-h treatment and to be inhibited by over 3-h treatment; When the magnetic field strength is more than 1.67 A/m, the reaction system is inbibited regardless of treatment time. Furthermore, the inhibitory effect of magnetic field increases with the increase of its strength. However, when the treatment time is over 1 h at the same strength, the effect of magnetic field tends to steady even if the treatment time extending. When the magnetic field strength is 4.22 A/m, it shows the strongest promotion effect on the PPO reaction system at 0.5 h and gradually presents the inhibitory effect after 0.5 h; Over 1 h, its inhibitory effect becomes steady with the Km of 0.0108 mol/L and Vmax of 0.0146 U/min. In conclusion, alternating magnetic field is able to inhibit the affinity of enzyme to substrate and decrease the maximum reaction velocity.

Key words: apple, polyphenol-oxidase (PPO), reaction kinetics, alternating magnetic field