## 1 Introduction  
Sustainable use of agricultural by-products is a key objective of the European Green Deal, which emphasizes resource efficiency and circular economy principles. One significant challenge in this context is the underutilization of sea buckthorn (_Hippocampae rhamnoides_) biomass. While the industry primarily focuses on berries, large quantities of biomass waste--particularly leaves and branches--are generated during harvesting and pruning yet remain largely unexploited. The sea buckthorn industry is dependent on its berries, but there are almost no applications for its secondary biomass use, which alone reaches about 12-15%. Valorizing this sea buckthorn biomass waste aligns with sustainability goals and can provide additional income for growers and rural communities [1]. In recent years, the interest and use of herbal infusions (extracts) from a wide range of edible plants have increased due to their potential health benefits and attractive flavor and taste. There is also growing interest in using sea buckthorn leaves and turning them into tea-type beverage products. However, most studies have focused on fresh sea buckthorn leaves, focusing on organic solvent extraction or sonication or microwave exposure to identify new compounds or maximize phenolic yield [2; 3; 4]. Less is known about the phenolic profiles and antioxidant activity of aqueous extracts of sea buckthorn leaves as tea product infusions and as beverages. It is known that biologically active compounds are sensitive to temperature changes, so it is important to apply innovative extraction methods. Pressure cyclic solid-liquid (PCSL) extraction using environmentally friendly solvents is suitable for this. However, this method has mostly been applied to sea buckthorn berries or pomace [5]. PCSL extraction is usually carried out by diffusion and osmosis, but it is difficult to find innovative methods based on the creation of a pressure gradient between solid and liquid matrices applied to sea buckthorn leaves in the literature. PCSL extraction preserves extracts containing biologically active compounds, thereby increasing the possibilities of using such extracts in the development of new value-added food products [6]. Compared to conventional methods such as maceration and liquid-liquid extraction, PCSL extraction has significant advantages, including significantly shorter extraction times, typically lasting from 2 to 24 h, lower temperature ranges, and the elimination of filtration steps due to the high quality of the extract produced [6]. This makes this extraction particularly suitable for the extraction of thermolabile substances, as it effectively avoids the decomposition that can occur during heating processes [7]. In parallel with extraction innovations, there is increasing consumer interest in fermented beverages such as kombucha, traditionally made from green and black teas. Kombucha is produced using a symbiotic culture of bacteria and yeast known as _Medusomyces gisevii_ (SCOBY) [8], which ferment sweetened tea. This raises the potential to incorporate novel infusions--such as sea buckthorn leaf extracts--into the kombucha fermentation process. However, no scientific publications to date have assessed the efficacy of kombucha products derived from sea buckthorn leaf extracts. Moreover, ensuring the microbiological safety of fermentation processes is a growing regulatory concern. In 2021, the European Food Safety Authority (EFSA) published requirements for the whole-genome sequencing of microorganisms used in food chains [9], aiming to ensure traceability and safety. Shotgun sequencing, a high-throughput DNA sequencing technique, enables the analysis of entire microbial communities and their functional potential [10]. This is especially important in kombucha cultures, which vary in microbial composition and include complex interactions between yeast and acetic acid bacteria [11].