## 5 Conclusions  
Tannins are bioactive compounds with a wide spectrum of applications, ranging from food and feed additives to pharmaceuticals, cosmetics, and traditional uses such as wine-making and leather tanning. As the global demand for tannin-rich products grows, interest in developing more efficient and selective extraction methods also increases. Currently, conventional aqueous extraction remains the primary industrial method. However, it often suffers from limitations such as poor selectivity, long processing times, and high energy requirements due to elevated temperatures and high amounts of water evaporation from the tannin extract.  
As a response, alternative extraction technologies are being explored, among which is supercritical fluid extraction (SFE), which has emerged as a promising solution. SFE offers precise control over process parameters--including pressure, temperature, and co-solvent concentration--enabling the selective targeting of specific tannin types (e.g., hydrolyzable or condensed tannins), depending on the desired application.  
Among the various supercritical fluids investigated, carbon dioxide (CO\({}_{2}\)) is most frequently used due to its moderate critical parameters, non-toxicity, and cost-effectiveness. However, its poor polarity limits its ability to extract polar compounds such as tannins. This limitation can be addressed through the addition of polar co-solvents (e.g., water, ethanol, or methanol), which improve solubility and extraction yield by modifying the overall polarity of the fluid mixture. Moreover, CO\({}_{2}\) use reduces the critical conditions of the system, lowering energy consumption.  
SFE systems offer further advantages, such as low viscosity, high diffusivity, and enhanced mass transfer rates, all of which contribute to improved process efficiency. The use of SC-CO\({}_{2}\) in combination with water has been particularly effective, with reported tannin extraction yields reaching up to 35%. However, tannin extracts may contain their degradation products, resulting from high temperatures or the reactive nature of supercritical water or alcohols.  
This reactivity can lead to unwanted by-products, but it also enables the creation of valuable compounds for industrial use. However, the mechanisms behind these transformations remain insufficiently explored, necessitating further investigation to recognize their potential fully.  
Despite the proven versatility and commercial viability of SFE, its application to tannin extraction remains relatively new and under active development. Significant research gaps remain, particularly in process scale-up, optimization, and environmental impact assessment. While environmental concerns related to SFE typically focus on energy demand (for solvent heating and gas compression) and the use of organic co-solvents, these issues are context-dependent. SFE may offer a more sustainable alternative than conventional organic solvent-based methods, particularly when using food-grade or recoverable solvents like ethanol. Therefore, supercritical fluid extraction represents a promising, tunable, and efficient approach for tannin recovery. Continued research and process development are essential to realize its full potential and to address current technological and environmental challenges.  
Conceptualization, I.J.-S. and P.S.; methodology, P.S.; validation, J.H. and I.J.-S.; formal analysis, I.J.-S.; investigation, P.S.; data curation, J.H. and I.J.-S.; writing--original draft preparation, P.S. and I.J.-S.; writing--review and editing, J.H. and P.S.; visualization, P.S. and J.H.; supervision, J.H. and I.J.-S.; project administration, J.H.; funding acquisition, J.H. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.