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 ls, respectively. The CD analysis showed that the PEF treatment caused a loss of a-helix and increase of b-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.

Analysis of α‐helix unfolding in the pine nut peptide Lys‐Cys‐His‐Lys‐Pro induced by pulsed electric field

“…When the electric field frequency was set at 2400 Hz, with the electric field intensity increased from 5 to 20 kV cm −1 , the relative -helix content of KCHKP was reduced gradually, reaching a minimum of 94.95% ± 0.71% at 5 kV cm −1 . A comparison of the relative -helix content at the same electric field strength revealed that changes in the -helix structure of KCHKP were more dramatic after treatment at 1800 Hz than after treatment at 2400 Hz, consistent with a previous report 12 showing loss of the -helix secondary structure following PEF treatment. On the basis of these analyses, we used an electric field intensity and pulse frequency of 10 kV cm −1 and 1800 Hz, respectively, as optimal conditions for subsequent experiments.…”

“…found that PEF treatment resulted in inactivation of pepsin activity, a gradual disruption of the β‐sheet structure and the emergence of random coil regions . Moreover, PEF treatment was shown to eliminate the α‐helix structure in several α‐helix dominant enzymes, such as polyphenol oxidase, lysozyme and peroxidase . However, most of these studies have been elementary structural analyses and have not revealed the crucial functional mechanisms of PEF treatment.…”

High‐Intensity Pulsed Electric Fields Processing Parameters Affecting Polyphenoloxidase Activity of Strawberry Juice

“…The circular dichroism analysis revealed a change in the secondary structure of the enzyme with a significant reduction of 50.72% in the relative α‐helix fraction of PPO. In the same way, Luo and others (2009) reported that a commercial extract of PPO was reduced by 69% when treatments of 24 kV/cm were applied for 320 μs. They also confirmed that HIPEF treatment caused a loss of α‐helix and increase the β‐sheet content, indicating that conformation changes occurred in the secondary structure of the enzyme.…”

Quality Changes in Mango Juice Treated by High-Intensity Pulsed Electric Fields Throughout the Storage

“…The application of thermal treatment to MJ significantly reduced activity of PPO and POD up to 55.5 ± 0.5 and 20.7 ± 1.0 at day 0 (table 1). The PPO and POD molecular structure, which contains a prosthetic group in their structure, has been reported to be specially affected by pH, temperature and electric fields (Luo et al 2010). Otherwise, RA LOX after thermal treatment increased at day of processing, LOX appeared to be less thermo-sensible.…”