# Bioconversion of Apple Pomace to _Meyerozyma guilliermondii_ and _Scheffersomyces stipitis_ Biomass
## 3 Results and Discussion
### The Results of the Yeast SCP Cultivation in the AP Hydrolysates
It must be mentioned that even if the assimilation patterns of the basic compound are similar for both strains, the final concentrations of biomass depend on many parameters such as strain characteristics, media composition (i.e., initial raw material, sugar content, inhibitors presence, pH, vitamins), the temperature, and the cultivation period; thus, the final concentration of the biomass is subject to significant fluctuations [60; 61; 87]. When comparing literature data, it should also be recognised that within individual species, different strain varieties may differ from the base strain in assimilating particular compounds and resistance to inhibitors present in lignocellulosic hydrolyses. All this can translate into substantial differences in biomass and metabolite production. Over 30 g/L of sugars were present in the hydrolyses obtained from AP; however, the final biomass yield differed significantly depending on the hydrolysis method. Lower yields were observed for the hydrolyses obtained after pretreatment with only water. This may be the result of the possible presence of non-estimated inhibitors. Values of biomass yield expressed as the amount of biomass per consumed sugars varied from 0.274 g/g for the MgWE30 sample to 0.441 g/g for the MgAE30 sample (Figure 1); this indicates that at least 40% of accessible sugars were converted into SCP DM, which in light of literature data for lignocellulosic hydrolyses and the similarity to our strains (_Scheffersomyces_ sp., _Candida_ sp.) [53; 54], may be considered a high and promising result. What is noteworthy is that in today's yeast factories, this value typically does not exceed 50% (0.5 g/g) [47]. During _M. guilliermondii_ cultivation in sugar cane bagasse hydrolysate, [PERSON] et al. [62] noted 24.4 g/L of yeast DM in a medium containing around 60 g/L of xylose and glucose. [PERSON] et al. [63], and after cultivating the same genus strain in rice straw hydrolyses \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Pretreatment** & \multicolumn{2}{c}{**Temperature of**} & \multicolumn{1}{c}{**Biomass**} \\  & **Method** & **Enzymatic** & **Yeast Strain** & **Concentration** \\  & & **Hydrolysis** [\({}^{\circ}\)C] & & **[g DM/L]** \\ \hline MgWE50 & water & 50 & & 8.55 \(\pm\) 0.28 \\ MgAE50 & 2\% acid & 50 & _Meyerozyma_ & 16.29 \(\pm\) 0.65 \\ MgWE30 & water & 30 & _guilliermondii_ & 9.12 \(\pm\) 0.48 \\ MgAE30 & 2\% acid & 30 & & 12.69 \(\pm\) 0.53 \\ SsWE50 & water & 50 & _Scheffersomyces_ & 10.71 \(\pm\) 0.23 \\ SsAE50 & 2\% acid & 50 & _stipitis_ & 14.63 \(\pm\) 0.36 \\ SsAE30 & 2\% acid & 30 & & 9.82 \(\pm\) 0.14 \\ SsWE30 & water & 30 & & 13.03 \(\pm\) 0.19 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Yeast biomass concentration. containing about 60 g/L of assimilable sugar, 7 g/L of yeast biomass was observed. Similar values were reported by [PERSON] et al. [88] (Y\({}_{\rm x/s}\) yield 0.52 g/g corresponding to 25.26 DM g/L for _M. guilliermondii_ isolated from Amazonian termites) and [PERSON] et al. [64], corresponding to 22 g/L after cultivation of _M. guilliermondii_ strain in sugarcane bagasse hydrolysate. For the _S. stipitis_ strain cultivated in brewers' spent grain hydrolysate, a Y\({}_{\rm x/s}\) equal to 0.46 g/g was noted by [PERSON] et al. [89]. After converting potato peels and sugar beet bagasse, 8.6 g/L and 8-10 g/L of _S. stipitis_ biomass were obtained by [PERSON] and collaborators [50; 58]. The results of the conversion of sugars to biomass obtained within the framework of the present work are, from an economic point of view, promisingly higher than those presented by [PERSON] and [PERSON] [90] for the _S. cerevisiae_ strain cultured in apple pomace hydrolysate (0.23-0.35 g/g). [PERSON] et collaborators [60] reported for aerobic batch cultivations in minimal media containing 20 g/L of glucose, that the sugar-to-biomass conversion ratio was 0.17 g/g for the _S. cerevisiae_ strain and 0.55 g/g for the _S. stipitis_ strain.