## 3 Results
### Apple Pomace and Its Hydrolysate as a Culture Medium for Yeast  
The growth of the selected yeast strains at 15 \({}^{\circ}\)C was calculated by counting the values of CFU/mL before and after 5 days of the fermentation process. The objective of this experiment was to evaluate the effect of the relation between inoculum size and biomass increase during fermentation of apple pomace. In the literature, various inoculation rates were used, for example, 2-20% in winemaking and 5-10% in brewery [41; 42; 43]. In the  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Concentration [g/L]**} \\ \hline  & **Arabinose** & \begin{tabular}{c} **Galacturonic** \\ **Acid** \\ \end{tabular}  & **Raffinose** & **Glucose** & **Fructose** & **Sucrose** \\ \hline Untreated AP & 0.10 \(\pm\) 0.03 & 0.06 \(\pm\) 0.01 & 0.07 \(\pm\) 0.02 & 2.22 \(\pm\) 0.39 & 6.66 \(\pm\) 1.08 & 7.36 \(\pm\) 0.11 \\ \hline  & 0.25\_V & 1.42 \(\pm\) 0.27 & 3.57  
case of small inoculum doses (e.g., 1%), the nutrient limitation of the medium appears later. Most often, the initial number of yeasts is in the range of \(10^{5}\)-\(10^{6}\) CFU/mL of the fermentation medium, and this amount determines their optimal activity in technological processes [44]. This is confirmed by scientific studies which show that the initial amount of \(10^{6}\) CFU/mL determines the growth of yeast to the level of \(10^{8}\) CFU/mL [45,46]. The results are presented in Figure 2.  
The measured yeast growth confirms that all of the selected yeast strains were able to grow at the tested temperature of 15 \({}^{\circ}\)C and remained active throughout fermentation. It can be seen that the cell growth of the examined yeast strains was around \(10^{8}\) CFU/mL. Slightly higher results were obtained for _Kazachstania barnettii_ D1 when using hydrolysed apple pomace as a medium. The highest final CFU/mL value was detected at 10% for both untreated and hydrolysed apple pomace. For the _Hanseniuspora uarum_ D9 and _Wickerhamomyces anomalus_ D11 yeast strains, the difference between the CFU/mL values at the starting point and after cultivation was the largest in the samples with 5% inoculation. A similar result for the total number of cells in CFU/mL after 5 days of cultivation at 15 \({}^{\circ}\)C was observed for the _Wickerhamomyces anomalus_ D11 yeast strain for the sample with 1% inoculum. All of the examined yeast strains performed well and yielded results suggesting that their adaptation to a low temperature before conducting the main process was successful. In general, the number of cells remained similar regardless of the level of inoculation. The numbers of yeast cells expressed in CFU/mL after 5 days of cultivation did not differ significantly whether 1%, 5%, or 10% of inoculum was used. An important fact influencing the above process is the size of the yeast culture and thermal treatment of apple pomace. Moreover, before the fermentation process, the medium was subjected to thermal treatment to sterilise the environment through the thermal inactivation of the natural microflora of the pomace. Under model conditions, the initial dose of inoculum did not significantly affect the growth of yeast biomass. However, the trend described in the scientific literature has been maintained--as the inoculum increases, yeast propagation in the environment is faster, and microorganisms are more active and  
Figure 2: CFU/mL values of examined yeast strains before and after fermentation of untreated and hydrolysed apple pomace. Abbreviations: 1%, 5%, and 10% refer to samples with various inoculation levels; “AP” refers to apple pomace untreated with enzymes; “H-AP” refers to hydrolysed apple pomace treated with 0.25 mL of Viscozyme® and 0.25 mL of Rohament® CL enzymes. produce more repeatable experimental results [44]. On the other hand, the sterilisation of waste materials is not practiced in the industry as biomass valorisation is carried out on large amounts of plant material.