## 1 Introduction  
Bananas are tropical plants [1] and the fourth most important food crop in the world after rice, wheat and corn. They are an important source of nutrition for many people around the world because they are available in large quantities all year round [2, 3]. This fruit is a rich source of starch, fibre, vitamins A, B, C and E, and minerals (potassium, phosphorus). A quantity of 100 g of peeled banana contains as much as 360 mg of potassium, which has a positive effect on the functioning of the heart muscle [4]. In addition, bananas are characterised by a high content of natural, bioactive nutrients--carotenoids and phenolic compounds. They have antioxidant, anti-inflammatory, antibacterial and anti-cancer effects [5]. The peel surrounding the edible part is the main waste when eating bananas. Banana peels (BPs) make up about 38% of the total banana weight. With around 140 million tonnes of bananas produced worldwide annually, BPs are a potential environmental pollutant [6; 7]. Banana peels contain valuable compounds that can be used primarily in the food industry [8]. They are rich in bioactive compounds such as tannins, flavonoids, alkaloids, glycosides, terpenoids and anthocyanins. In addition, they are rich in dietary fibre, protein, amino acids, polyunsaturated fatty acids and potassium. The compounds mentioned in the abovementioned waste can improve the nutritional quality of certain food products [6; 9]. Banana peels can be used as feed additives due to their positive composition. Thanks to their tannin content, they have a positive effect on cows' milk yield and protein content [10]. BPs can be used to make silage to extend the feed suitability. The BP silage production process is similar to other 'traditional' plant-based raw materials [10]. Peels can also be used as fertiliser for plants. Due to their high potassium content, amino acids, and growth stimulants, they contribute to increasing the germination rate of seeds. Another important aspect is that they deter aphids, pests that contribute to the destruction of cultivated plants [11]. Based on predictions, the global population's protein requirement exceeds 200 million tonnes for human nutrition [12; 13]. Animals consume at least a comparable amount of protein annually, and these trends indicate continued growth [13; 14]. Agriculture, facing challenges from a changing climate, may struggle to meet these needs fully [15; 16; 17; 18]. Consequently, there is growing interest in alternative protein sources, such as microbial protein. Single-cell protein includes both whole microbial cells and proteins that are extracted from their biomass [19]. It is believed that the term SCP (Single Cell Protein) was first used by scientists at the Massachusetts Institute of Technology around 1966. Initially, the term referred only to microbial biomass containing proteins, but now it refers to both biomass and protein isolates from microbial cells (bacteria, algae, yeasts and moulds) [19]. Common substrates that can be used to produce different types of single-cell protein are whey, sugar cane bagasse, orange waste, rice husks and beet pulp. This makes it possible to reduce the impact of organic waste on the environment and convert it into animal feed [20]. The possibility of producing SCP carries many advantages, making it a much better solution than plant or animal protein. The main benefit is the significantly short generation time of microorganisms and the high protein content in the cells. It is also possible to modify the proteins' amino acid profile by adjusting the substrate's composition, the cultivation conditions, or the cultivated strain's genetic modification. It is also worth noting that the production of this protein can be carried out in processes isolated from the environment, which are not influenced by climatic factors [21]. The use of yeast in animal nutrition offers many benefits. It is a rich source of B vitamins, enzymes and highly digestible proteins. Yeast is becoming increasingly important as a carrier of bioelements.