## 1 Introduction  
Grape cultivation is one of the most lucrative and traditional crops in the world and is known for its beneficial effects on human health [1]. With an annual production of more than 70 million tons, grapes are among the fastest-growing fruit crops worldwide (OIV, 2018) [1]. The International Organization of Vine and Wine (OIV) estimates that there were about 7.6 million hectares (mha) of vines worldwide in 2017, while 20 million tons of wine by-products are generated each year, corresponding to 30% of the total quantity of vinfied grapes [1]. However, the winemaking process, along with the pressing and maceration of the grapes, produces not only wine but also a large volume of organic waste. This waste includes the grape seeds, which account for the largest proportion of the waste (62%), but also the lees (14%), stems (12%), and dehydrated sludge [2, 3]. For many years, these by-products have mainly ended up in landfills, but in recent years there have been several attempts to introduce them into various industries, one of which is the cosmetics industry [3]. These efforts have become imperative, as grape by-products present significant environmental problems, mainly due to their low pH and high content of phenolic compounds. These compounds are resistant to biodegradation since they have phytotoxic and antibacterial activity. Grape seeds contain a high percentage of organic carbon (31-54%), which contributes to water pollution and the emission of unpleasant odors. In addition, the parasites and tannins found in these grape residues, together with other compounds, can negatively affect the flora and fauna of the area [3,4]. The importance of the circular economy of the by-products of oenology becomes even more significant when considering the rate of disposal of oil pomace, which constitutes seven million tons per year [1]. This is because, in the context of the circular economy, these by-products are not treated as waste, but as secondary raw materials that can be used to produce new value-added products. This model aims to reduce waste, maximize the use of resources, and create sustainable industrial processes [5]. The by-products of winemaking support the circular economy model, with applications in various sectors beyond the cosmetics sector. In the food industry, they increase the antioxidant activity and shelf life of products [5]. In the energy sector, they play an important role in the circular economy, as they are transformed from waste into valuable sources of biofuels. Their use for the production of biodiesel, bioethanol, and biogas reduces dependence on fossil fuels and minimizes the environmental footprint [6, 7, 8]. In the agricultural sector, they can improve soil fertility and reduce pollution. Their high polyphenol content ensures the controlled release of nutrients [9] and helps in decontamination from chemical pollutants [10]. These applications support sustainable agricultural practices and reduce the environmental footprint. Research on the by-products of winemaking should focus on optimizing the extraction parameters to achieve maximum yield and quality of bioactive compounds. Advanced extraction techniques, such as supercritical fluid extraction (SFE), have already proven to be more efficient than traditional methods, as they require fewer solvents, reduce processing time, and are more environmentally friendly [11, 12, 13]. At the same time, it is necessary to focus on improving the bioavailability of extracts so that bioactive compounds can be absorbed and utilized more efficiently by the human body or maintain their stability in cosmetics and food. Encapsulation techniques, for example, can protect compounds from degradation and increase their shelf life and future research should prioritize enhancing these techniques to improve the stability, bioavailability, and targeted delivery of bioactive compounds, ensuring their maximum efficacy in industrial applications [14].