## 4 Conclusions  
This study examined fibres and pomace from chokeberry, currant and apples. The physical properties of the powders, such as water content, water activity, colour, apparent and bulk density and microstructure, were studied. The most important point of the work was the thermogravimetric analysis and sorption properties of the materials studied. The determined kinetic curves, rate dependence curves and water vapour sorption isotherms made it possible to learn about the hygroscopic abilities of the materials studied. The chemical composition of the studied fibres and fruit pomace influenced the hygroscopic capacity. Pomace had a higher water content compared to the fibres. Chokeberry pomace showed the highest water content value, whereas chokeberry fibre had the highest water activity. All powders tested had water activity below 0.6, meaning that they were not exposed to the growth of microorganisms.  
Fibres were characterized by higher values of parameter \(L^{\star}\) which are responsible for colour lightness. Currant and chokeberry pomace and fibres had a higher proportion of red colour--parameter \(a^{\star}\)--while pomace and fibre from apples had a higher \(b^{\star}\) colour parameter, which accounts for yellow colour. Fibre and currant pomace showed the highest apparent density. Currant pomace and apple fibre had the highest bulk density value apple pomace. The tested materials were characterised by good or very good flowability and low-to-medium cohesion. Fibre and apple pomace showed the fastest water vapour adsorption, indicating that the highest hygroscopicity characterised them. The speed of water vapour adsorption was influenced by the water content: the lower the water content, the faster the water vapour adsorption. According to the course of the sorption, isotherms had a shape characteristic of type III isotherms. Apple fibre and pomace demonstrated the best hygroscopic abilities. Regarding thermogravimetric analysis, all pomace and fibres showed similar behaviour in the three main stages of weight loss. However, the weight loss and temperatures differ due to the chemical composition. Observation of microscopic images made it possible to conclude that the structure of apple fibre and pomace are similar to each other. The powders' structure from currant differed significantly: fibre had smaller particles with an elongated shape. At the same time, pomace was characterised by large particles with an irregular shape.  
Conceptualisation, S.G.; methodology, S.G.; software, A.P., L.K. and S.G.; validation, S.G.; formal analysis, L.K.; investigation, A.P., L.K. and S.G.; resources, A.P., L.K. and S.G.; data curation, A.P., L.K. and S.G.; writing--original draft preparation, A.P. and S.G.; writing--review and editing, A.P., L.K. and S.G.; visualisation, S.G.; supervision, S.G.; project administration, S.G.; funding acquisition, S.G. All authors have read and agreed to the published version of the manuscript.  
Figure 10: Microscopic photographs of the fibre (**E**) and pomace (**F**) of currant.  
Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The raw data supporting the conclusions of this article will be made available by the authors on request. Acknowledgments: The authors thank Greenfield Sp. Z o.o. for providing fruit fibres and pomace for the research, and [PERSON] for helping conduct the thermogravimetric analysis. Conflicts of Interest: The authors declare no conflicts of interest. References