## 2 Materials and Methods
### Evaluation of Enzymatic Activity of Yeasts: API ZYM  
The aim of the analysis was to evaluate the potential of utilising carbohydrates released from apple pomace. The enzymatic activity of the tested yeast isolates at their stationary growth phase was evaluated by API ZYM (bioMerieux, Marcy-I'Etoile, France) according to the manufacturer's instructions. API ZYM is a semi-quantitative method for the investigation of enzymatic activity. This technique is applicable to all types of samples (microorganisms, cell suspensions, tissues, biological fluids, etc.). It enables the systematic and rapid study of 19 enzymatic reactions using very small sample quantities. The examined yeasts were subjected to an analysis of enzymatic activity at the temperature of 15 \({}^{\circ}\)C.  
Quantitative Analysis of Ethanol and Acetic Acid Produced During Fermentation Using High-Performance Liquid Chromatography (HPLC)  
Fermentation activity of examined yeasts was evaluated by measuring the concentrations of ethanol and acetic acid produced during the fermentation of apple pomace accord \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample Name** & **Enzyme Used for Hydrolysis** &
\begin{tabular}{c} **Amount of Enzyme per 1 g of** \\ **Dry Mass [mL]** \\ \end{tabular} \\ \hline
0.5\_R &
\begin{tabular}{c} Rohapect 10 L \\ \end{tabular} & 0.5 \\ \hline
0.25\_VR1 &
\begin{tabular}{c} Viscozyme® + Rohament® CL \\ \end{tabular} & 0.25 + 0.25 \\ \hline
0.5\_VR1 &
\begin{tabular}{c} Viscozyme® + Rohament® CL \\ \end{tabular} & 0.5 + 0.5 \\ \hline
0.25\_RR1 &
\begin{tabular}{c} Rohapect 10 L + Rohament® CL \\ \end{tabular} & 0.25 + 0.25 \\ \hline
0.5\_RR1 &
\begin{tabular}{c} Rohapect 10 L + Rohament® CL \\ \end{tabular} & 0.5 + 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._ing to the method used by [PERSON] and coworkers [30]. They were determined by high-performance liquid chromatography, Agilent, model 1260 Infinity (Agilent Technologies, Santa Clara, CA, USA) equipped with a refractometric detector which operated at 55 \({}^{\circ}\)C. An amount of 20 \(\upmu\)L of sample was injected, and the compounds were separated on a Hi-Plex H column (7.7 \(\times\) 300 mm, 8 \(\upmu\)m) at 60 \({}^{\circ}\)C (Agilent Technologies, Santa Clara, CA, USA). The liquid phase was 5 mM H\({}_{2}\)SO\({}_{4}\) with a flow rate of 0.7 mL/min. A mass spectrophotometer was used for a quantitative analysis of ethanol, working in selected ion monitoring (SIM) mode. Quantitative Analysis of Volatile Organic Compounds (VOCs) Produced During Fermentation Using SHS-GC-MS  
Biosynthesis of volatile organic compounds (VOCs) was examined by gas chromatography (GC) and mass spectrometry (MS) using the Static Headspace (SHS) technique according to the method described by [PERSON] and coworkers [31] with several modifications. The samples were stored in falcon tubes in a freezer at \(-\)25 \({}^{\circ}\)C. First, a qualitative analysis was conducted to identify VOCs in the samples. During analysis, the mass spectrometer was operated in full scan mode (a scan range of \(m/z\) 27-350 was acquired). The VOCs were identified by comparing the obtained mass spectrum to the mass spectrum of a standard substance and the mass spectrum from a mass spectrum library (NIST/EPA/NIH Mass Spectra Library, Version 2.0 g). A total of 29 compounds were identified. For the quantitative measurements, selected ion monitoring (SIM) mode was used. Examples of GC-MS ion chromatograms after qualitative analysis are in the Supplementary Materials (\"Supplementary reports S1-S6\"). Before qualitative and quantitative analyses, 8 mL of each sample was transferred to 20 mL vials, which were then sealed with an aluminium cap. The prepared vials were placed on the feeder plate of a Headspace Sampler. During the analysis, the autosampler transferred the samples to a heater, where they were thermostated for 20 min at 50 \({}^{\circ}\)C. During thermostating, the vial was shaken (71 shakes/min with an acceleration of 260 cm/s\({}^{2}\)).