2. Plasma Physics and SourcesPlasma is a quasi-neutral ionized gas state composed of ions, free electrons, atoms andmolecules in theirfundamental or excited stateswith a net neutral charge [12]. Based on the thermal equilibrium, plasma can beclassified as thermal and low-temperature plasma. In thermal plasma, all species exist in a thermodynamicequilibrium (e.g., arc plasma; electron temperature _ heavier species temperature _ 10,000 K)whereas, in the other class, the temperatures of all species are the same in localized areas in theplasma. Low temperature plasma can be further subdivided into thermal plasma (quasi-equilibriumplasma), which are in a local thermal equilibrium state, and non-thermal plasma (non-equilibriumplasma), where species are in thermal non-equilibrium (e.g., glow discharges; electron temperature_ 10,000–100,000 K, heavier species temperature _ 300–1000 K) [2]. The non-thermal plasma,where electrons and heavier species are in thermal non-equilibrium, is referred to as cold plasma inthis review. Depending on the pressure conditions, plasma can also be classified as high-pressure,atmospheric pressure and low-pressure plasma. In atmospheric pressure plasma, plasma is generatedat the normal atmospheric pressure, eliminating the need for cost-intensive reaction chambers tomaintain pressure.Plasma can be generated using any kind of energy which can ionize the gases, such as electrical,thermal, optical (UV light), radioactive (gamma radiation) and X-ray electromagnetic radiation.However, electric or electromagnetic fields are widely used for CP generation [13]. The versatility of CPgeneration sources offers unique designs which are compatible with current food industry equipment.With regards to food processing, dielectric barrier discharge and jet plasma are most commonly used(Figure 1). Dielectric barrier discharge (DBD) devices consist of two metal electrodes, where at leastone of these electrodes is covered with a dielectric barrier. Dielectric barriers act as a stabilizingmaterial, avoiding any arc transition, and help in creating a large number of micro-discharges forhomogeneous treatments. Plasma jet devices consist of two concentric electrodes, where the innerelectrode is typically connected to a radio frequency power at high frequency causing ionization of theworking gas, which exits the nozzle and gives a ‘jet-like’ appearance. Further details of these systemsare available elsewhere [14–16].