Conformation changes of polyphenol oxidase and lipoxygenase induced by PEF treatment

Abstract

Inactivation of polyphenol oxidase (PPO) and lipoxygenase (LOX) by pulsed electric fields (PEFs) has been investigated using a coaxial treatment chamber. Circular dichroism (CD) and fluorescence analysis have been used to study conformation changes in the protein. The experimental results show that PPO and LOX can be effectively deactivated by the PEF treatment and that the effect on PPO and LOX increases with the increase of the applied electric field and the number of pulses. The activity of PPO and LOX can be reduced by 69 and 88% when fields of 24 kV/cm were applied for 320 and 962 μs, respectively. The CD analysis showed that the PEF treatment caused a loss of α-helix and increase of β-sheet content, indicating that conformation changes occur in the secondary structure of the PPO and LOX enzymes. The fluorescence intensity of LOX increases after the PEF treatment while, at the same time, increases in the applied electric field increases the intensity of the fluorescence emitted. These results prove the occurrence of local tertiary structure changes in the LOX protein.