pH-changes during pulsed electric field treatments — Numerical simulation and in situ impact on polyphenoloxidase inactivation

Pulsed electric field (PEF) treatment of liquid media was investigated with focus on the pH shifts occurring in a batch parallel plate electrode treatment chamber.A numerical simulation of pH-shifts during PEF application was performed, which was experimentally verified by the application of an optical method based on digital image processing.Numerical, as well experimental results showed pH-shifts of up to 4.04 units already after a treatment time of 34 μs at electric field strength of 10 kV/cm. As a result, pH values of 10.9 and 3.3 were observed at the cathode and anode respectively after PEF treatment of a salt solution with an initial pH of 7.1. Furthermore, it was shown that the PEF treatment may cause partial PPO inactivation not directly related to the electric field impact on the enzyme. This finding contributes to the understanding of PEF side effects, such as electrochemical reactions and pH changes during PEF treatments.

Industrial Relevance

Microbial and enzyme inactivation by PEF processing depends not only on treatment parameters, such as electric field strength, pulse number, temperature and frequency, but also on food properties, such as electrical conductivity, ion strength and pH. It has been widely reported that pH alters the microbial inactivation by PEF and also that PEF can produce pH-shifts. The presented investigation contributes to the understanding of pH-shifts by the application of PEF processing and the application of a simple digital imaging method for measuring and analyzing the pH during the PEF treatment, as well as, the understanding on PPO inactivation due to pH-shifts during PEF treatments.