## 3 Discussion  
The aim of this study was to investigate the effect of plasma water on the growth and catalytic activity of _Y. lipolytica_ yeast in the reactions of castor oil biotransformation to GDL and other metabolites. The research presented in the article was carried out using plasma water, under an air or nitrogen atmosphere, in a reactor patented by [PERSON] et al. [13] or commercially available Nantes plasma water (Boleslawiec, Poland) with the composition given in Section 4.2.3 with increased singlet oxygen content. According to literature data, water treated with low-temperature low-pressure plasma differs in physical and chemical parameters in relation to standard distilled water. These differences concern, e.g., water pH, conductivity, surface tension or the amount of oxygen dissolved in water [15]. The analyses of plasma water in different gas atmospheres conducted so far have shown that regardless of the gas environment in which the plasma is performed, the water macrostructure changes. It undergoes declustering, creating clathrates that are energetically stable and lose the ability to form gigaclusters [33]. However, the level of changes in the structure and physicochemical properties of plasma water depends on the plasma generation parameters and the time of its action on the water. The water used in our experiments was obtained as a result of the action of low-pressure, low-temperature, low-frequency glow plasma, under a pressure of 5 \(\times\) 10\({}^{-3}\) mbar, voltage of 600 V, 50 mA and frequency of 10 KHz [14]. The parameters of this treatment cause declustering of the water macrostructure with the simultaneous excitation of triplet oxygen molecules dissolved in water to the singlet state. Raman spectra indicate that singlet oxygen molecules are found inside plasma water clathrates [15]. It is also worth noting that in contrast to the commonly known plasma methods, plasma under reduced pressure, with the parameters described above, did not generate ozone or hydrogen peroxide in water, which are considered to be strong antimicrobial oxidizing agents [34]. Ozone participates in the oxidation of sulfhydryl groups, which are quite numerous in enzymatic proteins of microorganisms [35], while hydrogen peroxide generates hydroxyl radical OH\(\bullet\) intracellularly, which through the Fenton or Haber-Weiss reaction contributes to oxidative damage, stimulating the breakdown of the double helix of the DNA strand [36; 37]. The effect of using plasma water in a medium on the growth of _Y. lipolytica_ yeast cells was analyzed in the first stage of the research. In the aspect of GDL biosynthesis, it was important to verify to what extent plasma water stimulates or inhibits the growth of these microorganisms. The results of the measurements of the optical density OD\({}_{600}\) (Figure 1) and the yield of dry cell mass (Figure 2) showed that the use of plasma water contributes to the increase in the yield of yeast cell biomass and extends the duration of the stationary phase compared to the control medium (in which distilled water was used). The positive effect of plasma water was observed regardless of the gas atmosphere in which the water was treated by plasma. Clearly, the best results were obtained with the use of commercial Nantes plasma water. It was characterized by an increased content of singlet oxygen. This was due to passing pure (100%) O\({}_{2}\) through the water. The oxygen content in Nantes water is around 8.13 mg/L, and the singlet oxygen content is around 10-12 mg/L. Compared to traditional water, this value is higher by approx. 2 mg/L; at a temperature of 25 \({}^{\circ}\)C and a pressure of 101.3 kPa, water contains approx. 6.04 mg/L of oxygen [38]. This higher concentration of oxygen content may be a key factor in increasing cell concentration in the medium. The use of oxygen-enriched air has become a common strategy for the production of various biological substances by means of whole-cell catalysis.