## 5 Effect of the Potato Protein Isolation Method on the Properties of the Obtained Preparations
[14], multi-modal resins under different pH conditions made it possible to obtain concentrates with high solubility of 70-80%, containing pure protease inhibitor fraction (20-21 kDa) from MIMI I-45 resin, and concentrates containing both patatin (41 kDa) and protease inhibitors differed in terms of color and chlorogenic acid content. [PERSON] et al. [72] showed, for example, that ultrafiltration allowed for obtaining potato protein concentrates with a concentration of more than 75%, similar to the expanded bed adsorption method. The membrane adsorber technique, developed on a laboratory scale, using ion exchange membranes [16] for the separation and concentration of protein fractions, was also proposed. The developed techniques of ion exchange chromatography made it possible to separate the potato protein fractions and obtain preparations with a reduced amount of glycoalkaloids [19; 73]. Already in the 1980s, [PERSON] and [PERSON] [22] used ConA sepharose followed by a DEAE sepharose step to isolate potato proteins. In studies conducted by [PERSON] et al. [18], the ion exchange column Q-Sepharose Fast Flow allowed the separation of proteins with a molecular weight ranging from 16 to 25 kDa from the patatin protein fraction (40 kDa). These authors believed that the combination of UF membrane and Q-Sepharose Fast Flow ion exchange chromatography could be used for the isolation of protease inhibitor proteins from potato fruit juice (PFJ) under industrial conditions. In the process of isolating proteins from waste by-products of the starch industry, it turned out to be important not only to reduce the degree of protein denaturation but also to reduce the interaction between the isolated protein and phenolic compounds, as well as solanine, which reduced the digestibility and absorption of proteins contained in the obtained preparations. The preparations obtained by thermo-acid methods contained significant amounts of glycoalkaloids, reaching 1612 mg/kg dry matter, which, according to [PERSON] and [PERSON] [32], resulted from the formation of complexes between proteins and glycoalkaloids during this process. The conducted research on the preparation of native protein preparations showing specific functional properties--which consisted of protein concentration using cold methods, such as acid coagulation, cryoconcentration, membrane techniques, gel and ion exchange chromatography, using macromolecule separation techniques based on such parameters as size and shape, hydrophobicity, surface charge and affinity--did not contribute to a significant reduction in the glycoalkaloid content in the obtained preparations [16]. [PERSON] et al. [16] concluded that the use of inexpensive adsorbents meeting criteria such as a reproducible high performance, low cost and availability on a large scale may be a promising possibility for isolating proteins from potato juice on an industrial scale. These authors used hydrated phyllosilicates (clay minerals) as cation exchangers for this purpose and showed that it was possible to reduce the amount of glycoalkaloids in the preparations in one step, together with the separation of the proteins. The phyllosilicates used by them are a natural and inexpensive adsorbent that could form hydrophobic bonds with a variety of organic molecules, including proteins. According to [PERSON] et al. [16], the mechanism of separation of patatin fractions and protease inhibitors with the use of clay minerals was related to the difference in their charge status. Protease inhibitors as molecules with a positive charge or in the form of molecules of neutral charge status react with negatively charged phyllosilicates, while proteins of the patatin group, being neutrally charged, should not be adsorbed by negatively charged surfaces above their isoelectric point (4.6-5.2). A limitation of this method may be the unequal distribution of charged patches over the surfaces of the protein molecules and the possibility of electrostatic interactions.