## 3 Results  
### Enzymatic Hydrolysis of Apple Pomace  
To ensure effective microbial growth, it is essential to provide carbohydrates in the fermentation medium as a carbon source. In the case of yeast, the most common are glucose and fructose. Data in the literature indicate that apple pomace contains 2.5-22.7% glucose and 11.5-49.8% fructose, respectively [32]. Moreover, apple pomace contains polymer fractions, including the soluble fraction pectin and the insoluble fractions cellulose, hemicellulose, and lignin [5; 33; 34]. Thus, conducting the process on a large biomass load presents technological problems. Firstly, pectins exhibit gelling properties that make it difficult to maintain a homogeneous fermentation environment. Secondly, insoluble fibre fractions are carbohydrates that are difficult for yeast to digest [35]. Therefore, the enzymatic hydrolysis of apple pomace was performed. In addition to better liquefaction of the fermentation substrate, hydrolysis leads to an increase in the concentration of carbohydrates assimilated by yeast. The addition of cellulolytic enzymes during biomass processing increases the release of glucose from lignocellulosic biomass by improving the access to cellulose [36]. The dry matter content of the analysed pomace was approximately 19-21%. Commercially available multienzyme preparations were used in the context of the applied nature of the research conducted. Two commercial preparations with pectinolytic properties and one commercial cellulolytic preparation were used for hydrolysis. They allowed for the experiment to be scaled up from the laboratory scale to the industrial scale. To choose the most suitable enzyme for use in the hydrolysis of the apple pomace prior to yeast fermentation, the degree of liquidity was calculated in the pomace treated with selected combinations of enzymes. The data for all the samples are presented in Figure 1.  
The apple pomace sample treated with 0.5 mL of Rohapect 10 L (0.5_R), 0.25 mL of Viscozyme(r) together with 0.25 mL of Rohament(r) CL (0.25_VR1), and 0.25 mL of Rohapect 10 L together with 0.25 mL of Rohament(r) CL (0.25_RR1) showed the highest percentage of liquidity. The initial mass of liquidity of each sample was 18 g. Comparing the overall mass of liquid in samples before and after hydrolysis shows that treatment with enzymes improved the degree of liquidity in the apple pomace. It was found that the most suitable sample contained 0.25 mL per 1 g of dry mass of Viscozyme(r) and 0.25 mL per 1 g of dry mass of Rohament(r) CL (indicated as 0.25_VR1) as it expressed a high percentage of overall liquidity. The obtained results prove that enzymatic hydrolysis could improve the liquidity of apple pomace by breaking down structural polysaccharides. These findings  
Figure 1: Degree of liquidity of apple pomace treated with various combinations of hydrolytic enzymes. Abbreviations are as defined in Table 1.  
align with previous studies on fruit by-product processing [37]. The combination of pectinases and cellulases proved to enhance substrate liquefaction and increased the content of sugars in the fermentation medium [38]. These findings highlight the importance of optimising enzyme selection and dosage, which is crucial for the efficiency of liquefaction and minimising processing challenges related to high viscosity and insoluble fibre fractions in apple pomace [39]. Yeast growth and fermentative abilities are strictly dependent on the amounts of carbohydrates present in the medium. Therefore, to further assess the properties of the prepared apple pomace used as a medium, the concentrations of selected carbohydrates were measured. Enzymatic assay kits by Megazyme were used to analyse raffinose, galacturonic acid, arabinose, glucose, fructose, and sucrose. The results are presented in Table 2. The combination of enzymes selected for the further experiments was highlighted.