## 4 Discussion
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Unit** & **Bioeractor Batch Culture** \\ \hline Initial concentration of carbon source (S) & g/L & 75 \\ Time (t) & h & 45 \\ Biomass yield (X) & g\({}_{\text{d.w.}}\)/L & 16.35 \(\pm\) 2.1 \\ Maximum concentration of GDL (L\({}_{\text{max}}\)) & g/L & 2.93 \(\pm\) 0.33 \\ Conversion yield of GDL per biomass formed (Y\({}_{\text{L/X}}\)) & g/gd.w. & 0.179 \\ Conversion yield of GDL per carbon substrate (Y\({}_{\text{L/S}}\)) & g/g & 0.039 \\ Volumetric rate of GDL production (q\({}_{\text{L/v}}\)) & g/L/h & 0.071 \\ Specific rate of GDL production (q\({}_{\text{L}}\)) & g/gd.w/h & 0.0044 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Kinetic parameters of \(\gamma\)-decalactone biosynthesis in a bioreactor batch culture of _Y. lipolytica_, according to the parameters in Table 4, determined on the basis of the Taguchi method. 87.6 mg/L. The authors report that faster mixing provides a better oxygen transfer to the medium. Similar relationships were shown in the study by [PERSON] et al. [40]. The most advantageous in terms of GDL production (110 mg/L) was the mixing speed of 600 rpm (with 0.9 vvm aeration). With 300 rpm slower mixing, the product concentration decreased by nearly 30% (80 mg/L). Increasing the mixing speed is not always associated with increasing the lactone concentration in the medium. However, it may increase its volumetric rate of GDL production. This is evidenced by the team of [PERSON] and [PERSON] [23], who, by increasing the mixing intensity from 400 to 600 rpm, observed a 4.5-fold increase in the aroma productivity (from 16 to 75 mg/L). The different speed of mixing did not affect the differentiation of the emulsification level, but it ensured better dispersion of air bubbles in the medium, increasing the interfacial surface. The emulsification of the medium is extremely important from the point of view of yeast growth (including growth rate). In a non-homogeneous medium, the lag phase can be even 60% longer [47]. The effects of worse homogenization of the substrates, resulting from low mixing values (200 rpm), on the growth of yeast and the duration of the lag phase can be seen in Figure 1 and Table 3. The yield of biomass in these cultures did not exceed 10 g CDW/L, and the lag phase lasted more than 10 h (Figure 1c,d). The lower efficiency of GDL biosynthesis in the media with agitation at the level of 200 rpm may also be the result of the lower hydrophobicity of yeast cells from these cultures (Figure 2c,d). In biotransformation reactions, there is direct contact of yeast cells with the substrate by adhesion of microorganisms to the surface of larger droplets or by adsorption of smaller droplets on the surface of yeast cells. Lower cell hydrophobicity results in lower levels of intermolecular interactions [35; 44]. The third parameter influencing the efficiency of GDL biosynthesis, according to the indicated Taguchi methods, is the pH of the substrate. Acidity influences the activity of enzymes in the \(\beta\)-oxidation pathway. Moreover, in the granulometric tests, it was proved that the size of hydrophobic substrate droplets in the medium also depends on the medium acidity--the droplet size decreases proportionally with the decrease in pH [48]. The optimal pH of lactone biosynthesis depends on the species and type of microorganisms. According to [PERSON] et al. [28], the yeast _Y. lipolytica_, despite the different pH of the medium, can regulate the relatively constant intracellular pH. [PERSON] et al. [21] report that the optimal pH in terms of lactone synthesis by _Y. lipolytica_ W29 is approx. 6.35. Higher acidity of the substrate (pH = 4.45 and lower) combined with a low concentration of dissolved oxygen selectively switches to other pathways in the \(\beta\)-oxidation cycle and affects acyl-CoA hydratase and 3-hydroxy-acyl-CoA dehydrogenase, resulting in 3-hydroxy-gamma-decalactone, dec-2-en-4-olide, and dec-3-en-4-olide. [PERSON] et al.