## 2 Nutritional Value of Potato Proteins  
Potato proteins are characterized by high nutritional value, comparable to proteins of animal origin. This has been confirmed by the research of many authors over several decades [4; 5; 10; 32; 35; 39; 40; 41; 42; 43; 44]. Despite the beneficial nutritional, health-promoting and functional properties of potato proteins, they are relatively rarely used in food production. This is due to a number of technological and economic limitations; however, the constant progress in methods of isolating proteins from plant materials, including potatoes, and in increasing the purity and homogeneity of the obtained preparations creates the basis for the development of food preparations with high nutritional and health-promoting potential, as well as technological potential. The nutritional value of proteins is related to the content of amino acids, their mutual proportions and digestibility. In potatoes, apart from protein-building amino acids, there are significant amounts of free forms of amino acids, which increase the nutritional value of potatoes as a food product [39; 40]. The high nutritional value of potato protein and its good digestibility has been confirmed by many studies [4; 5; 10; 32; 35; 41; 42; 43; 44]. Basic fractions thatbuild potato protein, i.e., albumin, globulins, glutelins and the so-called residual proteins, are characterized by high nutritional value, as evidenced by the values of indicators such as chemical score (CS), the index of essential amino acids or PER at the level of 57-69, 48-83 and 0.95-2.3, respectively [5]. The rather wide ranges of values of these indicators showed, first of all, the varietal differences. With respect to nutritive value, potato proteins are similar to proteins of animal origin and exceed most plant-based proteins [35]. On the other hand, the low amounts of the prolamine fraction proteins (around 4% soluble protein) show lower nutritional value. The studies presented by [PERSON] et al. [45] showed that the nutritional value of potato proteins was influenced by the potato variety, regardless of the color of the tuber flesh. Storage conditions such as time and temperature, especially in the interaction with the cultivar, also influenced the differentiation of potatoes in terms of the content of specific proteins and selected amino acids [39; 40]. Potato protein is characterized by a particularly high content of the essential amino acid lysine, which is distinguished among plant proteins, while the limiting amino acids are usually tryptophan, methionine and cysteine; in colored potatoes, leucine is found [45]. The most abundant in potatoes are the amino acids aspartic and glutamic acid and their amides. The protein fractions of albumin and globulin, glycoproteins with a degree of glycosylation of around 4% [46], belong to the group of proteins typical of potato and are referred to as patatin or tuberin [22]. These proteins, due to their presence in significant amounts (40-60% soluble potato proteins), are considered as storage proteins. They are distinguished from other fractions by their high nutritional value, good solubility in water or aqueous salt solutions and enzymatic and antioxidant activity [14; 17; 23; 27; 46]. Patatin proteins are characterized by a good balance of the amino acid composition and a higher content of the essential amino acid, lysine, than other plant-based proteins. For these reasons, their nutritional value exceeds most plant proteins, including lysine-poor cereal proteins, and is close to the nutritional value of hen egg proteins [34], considered to be one of the reference proteins. Isolated from potato juice in its natural or only partially denatured form, it can be a potentially beneficial food additive [10; 19; 47; 48]. The second-largest group of proteins, accounting for around 30% of all potato proteins, are protease inhibitor proteins. They show great diversity in terms of structure, molecular weight, isoelectric point pH and biological activity [31].