Metal release in a stainless steel Pulsed Electric Field (PEF) system: Part I. Effect of different pulse shapes; theory and experimental method

Abstract

Liquid pumpable food is mostly pasteurised by heat treatment. In the last decennia there is an increasing interest in so-called Pulsed Electric Field (PEF) treatment. During this treatment food is pumped between two metal electrodes and exposed to short high electric field pulses, typical 2–4 kV·mm − 1 during 1–10 μs. During this treatment the stainless steel electrodes are in direct contact with the food product. Associated with the charge that has to be exchanged at the interface of electrode and food, electrode material may be transferred from electrode to food. This transfer of material may cause serious electrode corrosion and adds metals to the food. The magnitude of material transfer depends on many factors such as current magnitude, pulse duration, pulse shape and fluid constitution. In this contribution the effect of three different mono-polar pulse shapes on treatment chamber corrosion is investigated. Experiments are carried out in an aqueous sodium chloride solution. The experiments showed that due to PEF treatment dissolved metals are present in the liquid. The four main elements of stainless steel, iron, chromium, nickel and manganese, have been considered in particular. These elements could only be detected in the liquid when it was repeatedly exposed to a Pulsed Electric Field treatment, which was realised by repeatedly circulating. From the experiments a relationship between dissolved metals in sodium chloride and the transferred charge is derived. With these values an upper limit for dissolved metals caused by PEF treatment can be defined. Industrial relevance This paper investigated the metal release in a stainless steel Pulsed Electric Field (PEF) system by considering the effect of three different pulse shapes. The theory and experimental method are given in detail. Also a relationship between dissolved metals and the transferred charge is derived. The author proposed to use mono-polar Pulse Forming Network (PFN) topologies with a transformer or parallel inductor instead of more complex symmetrical bi-polar topologies.