Pulsed light inactivation of horseradish peroxidase and associated structural changes

- Horseradish peroxidase was inactivated by pulsed light.
- Peroxidase inactivation by pulsed light is an all-or-none process.
- Pulsed light changes the secondary and tertiary structures of peroxidase.
- Pulsed light seems to provoke the ejection of the prostetic group of peroxidase.

Pulsed light (PL) is a non-thermal preservation method in which foods are subjected to one or several intense pulses of wide-spectrum light. Peroxidase (POD) is an enzyme that needs to be inactivated or inhibited because of its deleterious effects on the quality of fruits and vegetables. The feasibility of using PL to inactivate POD was tested and results explained based on measurements of UV-vis spectrum, far-UV circular dichroism and tryptophan fluorescence, and the phase-diagram method. PL reduced the activity of POD by more than 95% after applying 128 J cm−2. There was observed a decrease in the Reinheitzahl value and ellipticity and an increase in tryptophan fluorescence at incremental fluences, as well as linear phase diagrams. The study indicates that the inactivation of POD by PL is an all-or-none process related to loss of helical structure, weak unfolding and ejection of the prostetic group.