Quantification of metal release from stainless steel electrodes during conventional and pulsed ohmic heating

Abstract

Electrochemical reactions at the electrode-solution interface of an ohmic heater can be avoided or significantly limited by choosing appropriate processing conditions in relation to the food properties. In the present work the effect of the electrical parameters (electric field strength and frequency of the applied current signal) and product factors (halides concentration, electrical conductivity and pH) on metal release from stainless steel (type AISI 316 L) electrodes of a batch ohmic heater was investigated. In each experiment, the concentrations of the main constituents of stainless steel (iron, chromium and nickel) released in the heating medium were detected by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Atomic Absorption Spectrophotometry (AAS). Results showed that the rate of metal release from the electrodes to the heating medium depends on frequency and applied field strength. However, the use of ohmic heating at a higher frequency than conventional (50 Hz) can significantly (p ≤ 0.05) reduce the flux of metal ions from stainless steel electrodes. Moreover, it was also demonstrated that electrochemical phenomena occurring at the electrode-solution interface strongly depend on the composition, pH and electrical conductivity of the heating medium. Industrial relevance: The magnitude of electrode material released into the heating medium during ohmic processing depends on many factors, whose effects should be known in order to define optimal treatment conditions, electrode material and food properties able to avoid or minimize the undesired phenomenon of contamination of the food product, electrode-fouling and electrode corrosion. This paper contributes to clarifying the effects of electric field strength applied as well as electrical conductivity, pH, and presence of halides in the heating medium on electrode corrosion or release of electrode materials during high frequency (25 kHz, bipolar square wave) pulsed power OH in comparison with conventional (50 Hz sine wave) OH. Interestingly, the use of sufficiently large frequencies may avoid or reduce the extent of electrochemical reactions at the electrode interface, minimizing corrosion and leakage of metals to the heating medium, even when electrode material of low cost and electrochemically active like stainless steel is used.

Extraction of tomato by-products’ bioactive compounds using ohmic technology

“…Electrodes used stainless steel 316 and OH was performed at 25 kHz. This combination avoid corrosion and electrochemical reactions (Pataro et al, 2014). A function generator (Agilent 33,220 A, Bayan Lepas, Malaysia; 1 Hz-25 MHz and 1-10 V) connected to an amplifier system (Peavey CS3000, Meridian, MS, USA; 0.3 V-170 V) was used to control system.…”

Effects of ohmic heating on extraction of food-grade phytochemicals from colored potato

“…It is worth mentioning that the conditions under which this work was carried out e i.e. high frequency (25 kHz) and low electric field ( 30 V/cm) e are usually reported as being well suited for industrial applications (cheaper equipment and feasible power input) (Pataro et al, 2014;Sakr & Liu, 2014) At these electrical conditions the extraction yields of anthocyanins and TPC in potato tissue are enhanced by OH. Furthermore, extraction yields can be further improved at higher temperatures (i.e.…”

“…From the process point of view, working at high frequencies (i.e. >17 kHz) is more advantageous since electrolysis, electrode erosion and leakage of metals to the heating medium are effectively eliminated, ensuring the reliability of the system and the safety of the processed products, even when a lowcost and electrochemically active electrode material like stainless steel is used (Pataro et al, 2014;Sastry, 2008;Shynkaryk et al, 2010).…”

Influence of moderate electric fields on gelation of whey protein isolate

“…During heating phase and holding treatment, the MEF applied varied from 15 to 22 V cm -1 and 4 to 8 V cm -1 , respectively, whereas electrical frequency was of 25 kHz. At this high frequency, (25 kHz), electrochemical reactions at the electrode interface are reduced, thus minimizing potential corrosion and leakage of metals to the medium (Pataro et al, 2014;Pinto et al, 2013). Temperature measurement was performed as previously described for conventional heating.…”