## 4 Conclusions  
This study introduces a novel application of PCSL extraction for isolating biologically active compounds from sea buckthorn leaves. Six different extracts of sea buckthorn leaves were obtained with varying numbers of extraction cycles and durations. The highest amount of biologically active compounds (5.51 g\({}_{\text{CE}}\)/L of proanthocyanidins and 12.42 g\({}_{\text{GAE}}\)/ L phenolic compounds) was observed in extracts obtained using 60 cycles, each lasting 10 min. However, shorter extraction resulted in lower concentrations of biologically active compounds. The reduced extraction time is more environmentally friendly. Therefore, the L-4 extract, obtained through PCSL extraction with 20 cycles of 2 min each, was selected for kombucha preparation. The highest concentration of phenolic compounds and lowest antioxidant changes during fermentation were observed in sea buckthorn leaf kombucha L4-100, while the lowest phenolic compound content and highest antioxidant changes during fermentation were found in green tea kombucha G-100. Microbial analysis revealed that _M. gisevii_ MI-2 supports diverse and active microbiota beneficial for fermentation. The culture of _M. gisevii_ MI-2 has a broad microbial diversity (227 bacteria and 44 eucaryotes) suitable for fermented kombucha beverages. Most of them (77.8% eukaryote and 92.5% bacteria) have a microbiological impact and can migrate and stay in the fermented drink. Evaluation of microbial safety demonstrated that kombucha with sea buckthorn leaf extract had stronger antimicrobial properties against tested pathogens compared to traditional green tea kombucha. Furthermore, sensory analysis revealed greater consumer acceptability for kombucha beverages enriched with sea buckthorn leaf extracts.  
Considering the obtained results, secondary raw materials such as sea buckthorn leaves are not only nutritional materials but also could be used as bioactive compound sources. This approach highlights the potential for utilizing underappreciated biomass in creating functional foods that contribute to a more sustainable and circular economy.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15126608/s1](https://www.mdpi.com/article/10.3390/app15126608/s1)]([https://www.mdpi.com/article/10.3390/app15126608/s1](https://www.mdpi.com/article/10.3390/app15126608/s1)).  
Conceptualization, K.A., J.J. and I.M.; methodology, K.A., J.J. and I.M.; validation, K.A., J.J. and I.M.; formal analysis, K.A.; investigation, K.A., J.J., J.G. and I.M.; resources, A.S. and K.A.; data curation, K.A.; writing--original draft preparation, K.A., J.J. and I.M.; writing--review and editing, K.A.; visualization, K.A., J.J. and I.M.; supervision, K.A.; project administration, A.S.; funding acquisition, A.S., J.J., I.M. and K.A. All authors have read and agreed to the published version of the manuscript.  
The authors gratefully acknowledge the financial support provided by the Lithuanian Rural Development Program 2014-2020 under the activity \"Support for the creation and development of EIP activity groups\" project \"Circular manufacturing model for producing biologically active material\" No. 35 BV-KK-22-1-05005-PR001.  
Not applicable.  
All the data generated or analyzed within the frame of the present investigation are included in this manuscript.  
The authors declare no conflicts of interest.