## 3 Results and Discussion
### Biomass Concentration of Yeasts After Cultivation in Banana Peel Hydrolysates  
The aim of the efficient preparation of banana peel hydrolysates was to utilise them as a medium for yeast cultivation. In Figure 1, we have presented the results of the cultivation of two test yeast strains, _Scheffersomyces stipitis_ (S) and _Meyerozyma guillermondii_ (G), in hydrolysates obtained using various methods. The lowest biomass concentration of 4.77 \(\pm\) 0.21 g DM/L was observed after culturing _S. stipitis_ yeast in the reference hydrolysate obtained only by pressure-thermal treatment of banana peels. A statistically similar (\(p\) > 0.05) biomass yield was observed after cultivating the _M. guillermondii_ strain in the same medium (5.01 \(\pm\) 0.12 g DM/L) (Figure 1). The introduction of enzymatic treatment following pressure-thermal pretreatment resulted in a significant (\(p\) < 0.05) increase in the concentration of cultured yeast, to 7.46 \(\pm\) 0.28 g DM/L for the PTE + G sample and 7.68 \(\pm\) 0.22 g DM/L for the PTE + S sample. Substituting the pressure-thermal pre-treatment with microwave treatment (followed by enzymatic hydrolysis) resulted in a biomass yield of 6.91 \(\pm\) 0.23 g DM/L and 6.94 \(\pm\) 0.15 g DM/L for the ME + G and ME + S samples, respectively. The ultrasonic and enzymatic treatment sequence, the UE + G and UE + S samples, resulted in a final yeast yield of 7.02 \(\pm\) 0.25 g DM/L and 7.15 \(\pm\) 0.32 g DM/L, respectively. A statistical comparison of the source data showed that using different hydrolysis methods significantly (\(p\) < 0.05) changed the final biomass yield. In contrast, no statistically significant (\(p\) > 0.1) differences in propagation were observed between the strains used. Although it is difficult to find literature on the multiplication of biomass in experimental conditions similar to ours, we have seen several papers in which the authors used banana peels as a substrate for the multiplication of microbial biomass. [PERSON] et al. obtained 1 \(\times\) 10\({}^{6}\) cells in 1 mL sort within 24 h when cultivating _S. cerevisiae_ yeast [72]. [PERSON] and [PERSON] obtained 2.4 to 8.82 g DM/L of banana peel hydrolysate when cultivating _Cyberlindnera jadini_ yeast for 96 h. The biomass they obtained contained up to 10% crude protein (although the authors did not state whether the result was converted to dry cell mass) [73]. [PERSON] and [PERSON] fermented BP hydrolysate \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Galacturonic Acid** & **Succinic Acid** & **Formic Acid** & **Acctic Acid** \\ \hline \multicolumn{5}{c}{**Concentration [g/L]**} \\ \hline PT + G & 0.61 \(\pm\) 0.023 & 0.14 \(\pm\) 0.011 & 0.1 \(\pm\) 0.009 & 0.39 \(\pm\) 0.02 \\ \hline PT + S & 0.61 \(\pm\) 0.03 & 0.13 \(\pm\) 0.007 & 0.12 \(\pm\) 0.01 & 0.42 \(\pm\) 0.022 \\ \hline ME + G & 0.6 \(\pm\) 0.042 & 0.26 \(\pm\) 0.007 & 0.28 \(\pm\) 0.011 & 0.36 \(\pm\) 0.019 \\ \hline ME + S & 0.64 \(\pm\) 0.057 & 0.23 \(\pm\) 0.01 & 0.36 \(\pm\) 0.02 & 0.43 \(\pm\) 0.013 \\ \hline PTE + G & 0.9 \(\pm\) 0.075 & 0.25 \(\pm\) 0.012 & 0.17 \(\pm\) 0.015 & 0.41 \(\pm\) 0.013 \\ \hline PTE + S & 0.86 \(\pm\) 0.061 & 0.24 \(\pm\) 0.015 & 0.23 \(\pm\) 0.02 & 0.39 \(\pm\) 0.021 \\ \hline UE + G & 0.75 \(\pm\) 0.074 & 0.25 \(\pm\) 0.022 & 0.3 \(\pm\) 0.014 & 0.47 \(\pm\) 0.043 \\ \hline UE + S & 0.74 \(\pm\) 0.04 & 0.24 \(\pm\) 0.008 & 0.31 \(\pm\) 0.028 & 0.38 \(\pm\) 0.029 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Concentration of selected organic acids after yeast cultivation in banana peel hydrolysate. with _S. cerevisiae_ yeast, obtaining about 12 mg of protein per gram of hydrolysate after 8 days [74]. [PERSON] et al. [75] obtained up to 2 g DM/L after 4 days of cultivation of _S. cerevisiae_ yeast in banana peel hydrolysate. Comparing this result to our accumulation of protein and biomass, we obtained up to about 3.5 mg of protein per gram of hydrolysate in our experiments.