High-voltage electrical discharge

High-voltage electric discharge (HVED) technique is a sustainable technology involving the application of high voltages into an aqueous solution. It can be a good alternative as compared to thermal and conventional treatments. Figure 4a shows the mechanism of high-voltage electric discharge treatment. The two submersed electrodes having high voltage release energy through a plasma channel into the mixture causing the disturbance (Roselló-Soto et al. 2015). The principle of high-voltage electric discharge can be described in two phases: the first phase (prebreakdown phase) and the second phase (breakdown phase). The first phase involves the introduction of light shock waves to the food sample, thus forming small bubbles. Adjusting the electric field intensity leads to the initiation of breakdown phase, resulting in release of active ingredients from the sample. However, the modification of electric field should be performed carefully as transition from prebreakdown phase to breakdown phase (electrohydraulic phase) could lead to several effects such as strong shock waves, structural damage to the sample, plasma bubbles inside the sample and strong liquid turbulence (Li et al. 2019). Energy usage forms an important for better recovery of active compounds and determining the efficiency of the system. The energy of the treatment (Rajha et al. 2014; Barba et al. 2015) can be shown in Eq. (1) and Eq. (2):

where E is the specific energy (kJ/kg), m the product mass, W_HVED is pulse energy (kJ/pulse), V is the voltage (V) and I is the current applied (A).

a Mechanism of high-voltage electric discharge treatment (HVED) and b pulse electric field extraction (PEF) treatment

In recent years, the technology has been extensively used for extracting polyphenols from various foods like grapes (Brianceau et al. 2016), pomegranate peel (Xi et al. 2017), peanut shells (Yan et al. 2018) and papaya (Lončarić et al. 2020). The technology thus poses as a sustainable method for the extraction of polyphenols.