## 1 Introduction  
After the raw juice of vegetables or fruits is pressed, which can be further processed to produce concentrated juices, beverages, wines and more, a waste mass called pomace remains. Post-production pomace can account for 10% to as much as 60% of the initial weight of the raw material [1, 2]. It is estimated that the world fruit industry alone generates 0.5 billion tons of post-production waste annually, mainly pomace. Pomace and other by-products generated from fruit and vegetable processing are some of the richest organic materials obtained as by-products in the agriculture and food industry. Studies show that many valuable nutrients remain in the pomace, such as proteins, lipids, saccharides, fiber, vitamins, coloring and aromatic substances [1; 2; 3]. The industry, in line with sustainable development goals, is trying to use pomace for various purposes. In addition, food manufacturers are realizing that with the right technology, their processing is cost-effective and increases the company's product portfolio. However, the disadvantage of pomace is its high non-storability and susceptibility to microbial growth, which requires rapid processing and creates organizational difficulties in handling this material. In the food industry, pomace is processed for various purposes, including animal feed and isolation of valuable ingredients, for example, pectins, pigments and vitamins [4]. Moreover, pomace is also added to tea blends as an additive that enhances the desired flavor, aroma and color [5]. Fruit or vegetable pomaces are ideal as an additive that can enrich foods with proteins, vitamins, polyphenols, organic acids or minerals [6]. Another application is its use for ethanol and vinegar production [7]. An integral part of fruits and tomato pomace are seeds, from which high-quality oil can be extracted [3]. Pomace is also used for biotechnology purposes as part of the microbial growth medium and, most importantly, for biogas production [8; 9]. There are also attempts to extract plant pigments to dye wool fibers and other textiles [10]. Blackcurrant (_Ribes nigrum_ L.) is known for its strong health properties (antimicrobial, antioxidant, anti-inflammatory, facilitating the biosynthesis of collagen, aiding in the production of some peptide hormones, and many others) due to its high content of ascorbic acid, anthocyanins and flavonoids [11; 12; 13]. Studies have shown that currant pomace, along with that of grapes and chokeberry, contains a large amount of these components after the juice pressing process [5; 14]. In particular, anthocyanins are of interest because of their high content in the skin and because they can be extracted relatively easily. The extracted anthocyanins are used for pharmaceutical purposes and as a food coloring additive (E163). Ultrasound-assisted extraction (UAE) is an advanced technique that is being proposed as one of the sustainable alternatives to conventional extraction, showing the potential to reduce extraction time, energy and solvent consumption and simultaneously increase extraction yield [15; 16; 17; 18]. UAE is based on the interaction of high-frequency sound waves with the plant matrix. Cavitation, friction on interfacial surfaces, absorption of the acoustic wave energy, as well as the associated heat release, cause UAE to increase solubility, diffusion, solvent penetration and transport of compounds, greatly increasing efficiency [19]. Ultrasound is successfully used for the extraction of phenolic compounds, carotenoids, anthocyanins, oils, polysaccharides, etc., from various plant parts and agricultural by-products [15; 16]. Methanol, ethanol or acetone are best suited for extracting bioactive compounds from blackcurrant plant parts or pomace [13]. However, neither methanol nor acetone can be used to obtain extracts later used in food production. On the other hand, ethanol is an expensive solvent, so water or mixtures of water with ethanol are used for economical industrial extraction.