## 2 Materials and Methods  
### Experimental Setup  
A simplified scheme of the experimental setup is presented in Figure 1. The solid state microwave generator operating at 2.45 GHz (Sairem, Neyron, France, GMS 200 W) was connected by a coaxial cable to a commercial electromagnetic surface wave resonator (Sairem, SURFATRON 80). Microwave (MW) power supplied from the generator was adjustable in order to optimize discharge conditions; the powers of \(5\,W,7\) W and \(9\,W\) were used in the present study for the fruit surface treatment. The surfatron resonator was continuously cooled by the ambient air flow of 4 L/min at room temperature without any resonator water cooling. Argon (purity of 99.999%) flow of 7 L/min was controlled by OmegaFMA-A2408 or Voegtlin Red-y compact mass flow controllers. The discharge was created inside a quartz tube (with the real dielectric permittivity \(\varepsilon_{\mathrm{r}}\) = 3.2541 and imaginary one \(\varepsilon_{\mathrm{i}}\) = 0.0062) with 8 mm outer diameter and 3 mm inner diameter. The ambient air (temperature of 25 \({}^{\circ}\)C at a relative humidity of (35 \(\pm\) 2)% was surrounding the plasma effluent just behind the resonator. The system axis was installed vertically with the gas flow from top to bottom (see Figure 1).  
Visual observations of the plasma torch and its dependence on the MW power were made using a SONY (Sony Corporation, Minato, Tokyo) DSC-H7 camera with an exposure time of 1/10 s. An FLIR (FLIR Systems, Wilsonville, OR, USA) E30 Infrared Camera was used for thermal imaging during the fruit plasma treatment.  
Optical emission spectrometry was used for the plasma diagnostics during the fruit treatment. The light emitted by the discharge was focused by a quartz lens (diameter of 25 mm, focal length of 35 mm) to the entrance (positioned at the lens focus) of a multimode optical cable connected to the spectrometer. This setting allowed proper measurement of emitted light in case the discharge channel was moving across the capillary diameter. Such an effect is well known from the literature [31]. A rectangular nonreflecting light guide made of black paper (wide of 25 mm, high of 0.4 mm) was installed at the optical axis horizontally in front of the lens to obtain a good axial resolution. A Jobin Yvon TRIAX 550 spectrometer (Horiba, France) with a LN\({}_{2}\) cooled back illuminated CCD (1025 \(\times\) 256, pixel size of 26 \(\times\) 26 \(\upmu\)m\({}^{2}\)) was used for the spectra acquisition. The whole spectra acquisition system was calibrated with respect to its spectral response using the standard Ocean Optics (Largo, FL, USA) DT-MINI-2-GS source and measured spectra were corrected with respect to the system spectral response for the plasma parameters' calculation. Bands of NO-gamma, OH (A\(\rightarrow\)X) and N\({}_{2}\) first negative and second positive systems and argon and oxygen atomic lines were determined in recorded spectra. Rotational temperatures were calculated using the Boltzmann plot methods from the OH (A\(\rightarrow\)X) 0-0 transition and the nitrogen second positive 0-2 band. Vibrational temperature was calculated by the same method, using the band head intensities of the nitrogen second positive +2 sequence. The excitation temperature of argon atoms was calculated from integral intensities of selected argon lines. All technical details of these calculations as well as spectra identification were published recently [32] and thus are not repeated here.  
Figure 1: Scheme of the experimental set-up. 1—gas tube; 2—mass flow controller; 3—quartz discharge tube; 4—coaxial cable; 5—surfatron resonator; 6—antenna; 7—plasma torch; 8—vertically movable optical line (composed from parts 9–11); 9—black rectangular light guide; 10—quartz lens; 11—yellow optical filter (optional); 12—multimode quartz optical fiber; 13—treated berry.