## 3 Results and Discussion
### Water Vapor Sorption Kinetics of Fruit Fibres and Pomace  
The sorption properties of the studied fibres and pomace were analysed by determining kinetic curves, which show the dependence of the change in the amount of absorbed water with the duration of the process. The kinetic curves are presented as a graph in Figure 2.  
The best hygroscopic ability was shown by apple fibre, of which the amount of absorbed water after 120 h of the process was 73.77 g/100 g d.m. A much lower rate of water absorption was characterised by chokeberry and currant fibres, in which the amount of absorbed water was similar. The water content of the former increased by 26.65 g/100 g d.m., while in the latter by 27.20 g/100 g d.m. It was found that the water content stabilised after 60 h in chokeberry and currant fibres. In the final stage of the process, the water content of the chokeberry fibre and currant fibre was similar in shape. These materials, for the first 40 h of the process, intensively absorbed water, while after this time, water vapour adsorption stabilised. Apple fibre was hygroscopic for the entire duration of the process. The increase in water content in the last hours of the process indicates that the apple-derived material had not reached a state of moisture equilibrium [28]. The dependence of water content as a function of time was subjected to mathematical analysis, and the curves were described using an exponential equation. Parameter analysis of the exponential equation showed a good fit to the experimental data. The value of the coefficient of determination R2 was in the range of 0.971-0.995 (Table 6), which indicates a good description of the experimental data by the exponential equation. Analysing the kinetic curves of the pomace, it was observed that the apple pomace absorbed water the fastest. After 120 h, per 100 g of dry substance, it absorbed 58.03 g of water. Apple pomace showed significantly better hygroscopic abilities compared to the other extrudates tested. Pomace derived from chokeberry absorbed 34.33 g/100 g d.m. The least hygroscopic material was currant pomace, which absorbed only 31.52 g/100 g d.m. As in the case of fibres, the water content of chokeberry and currant pomace stabilised after \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Equation Coefficient** & **R2** \\ \hline \multirow{3}{*}{**chokeberry fibre**} & \(a=27.280\) & \multirow{3}{*}{0.981} \\  & \(b=0.889\) & \\  & \(c=0.051\) & \\ \hline \multirow{3}{*}{**apple fibre**} & \(a=75.399\) & \multirow{3}{*}{0.995} \\  & \(b=0.955\) & \\  & \(c=0.026\) & \\ \hline \multirow{3}{*}{**currant fibre**} & \(a=24.573\) & \multirow{3}{*}{0.971} \\  & \(a=0.897\) & \\  & \(c=0.057\) & \\ \hline \multirow{3}{*}{**chokeberry pomace**} & \(a=34.613\) & \multirow{3}{*}{0.985} \\  & \(b=0.908\) & \\  & \(c=0.044\) & \\ \hline \multirow{3}{*}{**apple pomace**} & \(a=57.145\) & \multirow{3}{*}{0.995} \\  & \(b=0.960\) & \\ \cline{1-1}  & \(c=0.034\) & \\ \hline \multirow{3}{*}{**currant pomace**} & \(a=30.215\) & \multirow{3}{*}{0.986} \\  & \(b=0.912\) & \\ \cline{1-1}  & \(c=0.055\) & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Parameters of the exponential equation describing the kinetics of water vapour adsorption by the studied fibres and fruit pomace. Figure 2: Water vapour kinetic curves of the time dependence of the amount of absorbed water in the tested fruit fibres. 60 h. The chokeberry pomace showed similar properties to the fibre of the same origin, as between 100 h and 120 h of the duration of the process, instead of being absorbed, it gave up 0.65 g/100 g d.m. As with the fibres, the course of the curves of chokeberry and currant pomace was similar in shape. The reduction in adsorption intensity occurred after 40 h of the process. Apple pomace did not reach a state of moisture equilibrium, as an increase in water content was noted of water in the last hours of the process.