## 1 Introduction  
Crisps are one of the most popular potato-based snack products. They are thin potato slices fried in hot fat for a short time [1]. Potato crisps are characterized by low moisture (about 2%), relatively high fat content (30-39%), golden-yellow color, a specific oil-potato flavor and aroma, as well as a crispy and delicate texture [2]. The raw material for the production of crisps should be characterized not only by the appropriate shape and size, but also by the suitable chemical composition (21-25% dry weight, 16-20% starch, and less than 0.25% reducing sugars) [3]. Blanching is a thermal process that is carried out in water, usually at 65-85 \({}^{\circ}\)C for 3-5 min. This treatment aims to reduce the content of reducing sugars in the raw material, thus obtaining the appropriate light color of the finished product. During blanching, enzymes may also be inactivated and other groups of water-soluble compounds removed, which would contribute to the formation of a too-dark color of the product [4]. Blanching also has a negative effect on other characteristics of potato crisps, mainly fat content and consistency. Although it was possible to select classic varieties with yellow flesh, characterized by a low content of reducing sugars and thus not requiring blanching, varieties with colored flesh usually have a higher content of these compounds and tend to burn. Therefore, it seems advisable to use blanching in their processing. This process also reduces the content of polyphenic compounds (namely phenolic acids and anthocyanins), which results from their good solubility in water as well as their sensitivity to high temperature [5]. The key solution in the technological process of producing crisps from potatoes with colored flesh may therefore be the selection of such blanching parameters that will allow crisps to be obtained with the desired color, and at the same time, the highest possible content of bioactive compounds. In the literature, there is no information about the effect of blanching on the content of kynure acid in crisps, for cultivars of potatoes with colored as well as for the classic color of flesh. However, so far, the use of cooking as a thermal process has not been shown to change the content of this acid in potatoes [6]. The next most important step in the production of potato crisps is frying. Vegetable oils are used for frying, and the process is carried out most often at a temperature of 175-185 \({}^{\circ}\)C for approximately 3-5 min. During the frying process, typical sensory features of the crisps are shaped, such as color and specific taste and smell, which are also dependent on the formation of Maillard reaction products [7; 8]. During frying, the product is almost completely dehydrated, and the frying fat takes the place of the evaporated water [2]. Frying, however, significantly reduces the content of phenolic compounds. [PERSON] et al. [3] showed that during the frying of crisps from the red flesh cultivars, the anthocyanin content was reduced by 40-60%, while purple ones, it was reduced in the range of 50 to 80%. In another experiment, [PERSON] et al. [9], analyzing the content of kynure acid, a tryptophan metabolite with health-promoting properties [10; 11; 12], in the raw material and finished products, found that potato crisps were characterized by a lower content when compared to raw potatoes. KYNA exhibits pro-health properties, including antioxidant, anti-inflammatory, and anti-convulsant properties. It was also reported that KYNA can have protective properties on the human brain and an inhibitory effect on the proliferation of colon cancer cells. It can be assumed that the use of a high-temperature process, such as frying, reduces the content of this acid in the finished product. However, the studies only concerned cultivars with yellow flesh [6]. Thermal treatments play a key role in the technological process of obtaining potato crisps. Both blanching and frying shape the quality of the final product.