Analysis of discharge parameters of an argon cold atmospheric pressure plasma jet and its impact on surface characteristics of White Grapes

An argon cold atmospheric-pressure plasma (CAP) jet operated using bipolar pulsed power supply has been characterised electro-optically and the discharge parameters are optimized. An analysis has been done on the impact of the argon CAP jet treatment on the surface properties of white grapes for different treatment time period. The developed argon CAP jet is a plasma source based on dielectric barrier discharge (DBD) that has been tuned at various input parameters including applied voltage, frequency, average power consumption, and argon flow rate. Optical Emission Spectroscopy (OES) is used to identify the generated species along with plasma parameters. The collisional-radiative (CR) model is employed to extract the electron density (ne) and electron temperature (Te) from the spectra at the optimised applied voltage of 4 kV, frequency 20 kHz and argon flow rate of 4 slpm. The OES results coupled with the CR model (ne similar to 1014 cm-3 and Te similar to 1 eV) and the plasma gas temperature measurement through OH (A-X) transitions (Tg similar to 310.5 K) show the non-equilibrium nature of the argon CAP jet. A comparative analysis between untreated and treated white grapes reveals that the argon CAP jet treatment influences surface microstructure, increasing hydrophilicity (with a similar to 49.3% decrease in water contact angle) along with slight changes in surface temperature (similar to 5 degrees C increase), colour (Delta E* < 1.5), and physiochemical properties such as chemical composition (no change) and Total Soluble Solid (TSS) content (similar to 8.3%). It is inferred that this type of CAP jet treatment of white grapes only affects the physical characteristics of the grape surface and does not alter any chemical compositions.