## 1 Introduction  
The growing global population has increasing demands for food, water, and energy. Increased production and consumption inevitably lead to the production of various types of waste, including agricultural, food, wood, municipal solid, and sewage sludge wastes. These wastes are directly connected to the core needs of food, energy, and water, which are vital for the sustenance and growth of human societies [1, 2, 3]. Their diverse composition and characteristics make them more challenging to manage uniformly. The improper management of waste biomass can lead to environmental issues, such as greenhouse gas emissions(particularly methane from decomposing organic matter) and the pollution of soil and water, as well as inefficient use of potentially valuable resources. Adequately processing and utilising waste biomass often requires specific technologies and infrastructures, such as facilities for composting, anaerobic digestion, or biomass-to-energy conversion. However, waste biomass can also serve as a renewable material capable of supplying sustainable energy and a range of bio-based materials. In the food industry, the apple juice sector generates notable amounts of waste by-products. According to the World Apple and Pear Association (WAPA), China is the leading producer of apples at about 36.09 million tons. Turkey, for the first time, secured the second position, increasing production from 4.44 to 4.66 million tons. The United States occupies the third place with 4.51 million tons. The fourth major global apple producer is Poland with 4.50 million tons [4]. The large-scale production of apples and, subsequently, apple juice results in significant quantities of waste biomass (approximately 25%), primarily in the form of pomace--the solid residue left after the extraction of juice, including the skins, pulp, seeds, and stems. Managing this by-product efficiently presents a substantial challenge as it constitutes a large portion of organic waste in the food processing industry. The most popular method of apple pomace disposal is to transfer it directly to the soil in a landfill. Due to the fact that this waste material contains more than 70% of water, carbohydrates, and organic acids, which lead to enhanced microbial fermentation, it may cause a serious pollution problem because the excessive growth of microorganisms may decrease the available nitrogen in the soil and truly affect the C/N ratio [5]. Nonetheless, the ready availability of apple pomace and its beneficial components for human health offer possibilities for economically viable post-processing opportunities [4; 6]. Apple pomace contains several notable compounds, including dietary fibres, polyphenols, and bioactive compounds such as phenolic acids (chlorogenic acid), flavonoids (catechins and epicatechins), and dihydrohalcone (phlorizin) [7]. The valorisation of apple pomace using microorganisms, particularly yeast, is attracting growing interest from both researchers and the food industry. Due to the relatively high amounts of carbohydrates in apple pomace, yeasts seem to be a good choice for reducing this type of by-product. Currently, many techniques of apple pomace management are available. Apart from the biofuel industry, where products are mainly fermented by microorganisms, existing techniques are mostly focused on the extraction of various compounds from the raw material [8; 9]. Such processes usually require expensive and specialised equipment, and they can generate wastes. However, the microbiological way of processing side-streams is the promising solution within the circular economy assumptions. The potential of apple pomace as a substrate for microbial growth is well known [5]. After fermentation, numerous compounds such as pectin, dietary fibre, xyloglucan, natural antioxidant, and aromatic compounds are extracted [10]. In recent years, the potential of non-_Saccharomyces_ yeast has been gaining recognition.