## 3 Results
### Apple Pomace and Its Hydrolysate as a Culture Medium for Yeast
Large amounts of inoculum allow for the control of the non-sterile environment and may inhibit naturally occurring microorganisms. [PERSON] and coworkers confirmed the correlation of the inoculum size and growth inhibition of undesired lactic acid bacteria in corn mash. By using higher inoculation rates, it is possible to inhibit the metabolism of contaminating _Lactobacillus_[47]. Another study was conducted by [PERSON] and coworkers, who analysed the effect of inoculum size on protein productivity during the fermentation process. They proved that a lower inoculation level leads to slower propagation of the environment by yeast, which determines decreased protein productivity. However, using too much yeast is also not beneficial because there is an overconsumption of carbohydrates during the adaptation phase, and it results in protein having lower productivity [48]. The concentrations of the selected carbohydrates in the untreated and hydrolysed apple pomace samples before and after yeast fermentation were examined using enzymatic assays for raffinose, galacturonic acid, arabinose, glucose, fructose, and sucrose. The data are shown in Figure 3.  
The content of arabinose in the pure apple pomace was found to be quite low. It was significantly improved by treatment with the selected enzymes, rising by almost 17 times. However, after fermentation, no notable decrease in the arabinose concentration was observed, meaning that this carbohydrate was not preferably utilised by the examined yeast strains. The most significant changes in concentration were detected in the case of _Hanseniagora__uvarum_ D9 after fermentation of untreated apple pomace with 10% inoculum. Figure 3: The carbohydrate contents in apple pomace samples before and after fermentation. Abbreviations: “Initial” refers to the carbohydrate content before the fermentation process; 1%, 5%, and 10% refer to samples with various inoculation levels; “AP” refers to yeast cultured with apple pomace untreated with enzymes; “H-AP” refers to yeast cultured with hydrolysed apple pomace treated with 0.25 mL of Viscozyme® and 0.25 mL of Rohament® CL enzymes. The increase in arabinose concentration may indicate the ability of this yeast to hydrolyse pectin, releasing sugar molecules [49]. The untreated apple pomace did not yield a high concentration of raffinose. The content of raffinose after enzymatic treatment was moderately improved. However, samples collected after 5 days of fermentation, whether using untreated or hydrolysed apple pomace, yielded very similar results to those measured before the process. This suggests that raffinose was not metabolised as a carbon source by the examined yeast strains since the concentrations before and after hydrolysis remained much the same. The content of galacturonic acid in the pure apple pomace was very low. After hydrolysis, the measured concentration was significantly higher due to the pectinolytic activity of the used enzymes. However, the results before and after fermentation did not differ significantly. For all examined strains, regardless of whether hydrolysis was conducted or not, the collected samples yielded results similar to those obtained before yeast fermentation. The concentration of glucose in the untreated apple pomace was quite high. Enzymatic treatment significantly improved the level of glucose. The sample collected after fermentation yielded a significantly lower concentration of glucose in all cases regardless of the inoculation level. This was to be expected since glucose is a preferred carbon source for yeast fermentation [50]. These results show that during fermentation, the glucose was almost completely utilised by the examined yeast strains. Fructose was the most abundant carbohydrate in the tested samples. This was expected as fruits such as apples are naturally high in fructose. The apple pomace that underwent enzymatic treatment showed an even higher concentration due to the enzymatic activity of the used commercial preparations.