## 3 Results and Discussion
### FIC and BI  
Thermal treatment during the production of potato crisps is of particular importance due to the Maillard reactions (non-enzymatic browning). This sequence of complex reactions leads to the formation of compounds responsible for the specific taste, smell, and color, being key factors in terms of the consumers' acceptance of crisps. During the advanced stage of the Maillard reaction, among others, fluorescent intermediary compounds (FICs) are formed. The intensity of their fluorescence is a useful indicator of changes in food products caused by thermal processes [26]. In non-blanched samples, the FIC levels were influenced by the frying temperature. In the case of both cultivars, the higher the temperature, the higher the FIC level (Table 6). Crisps made out of potatoes with purple flesh were characterized by a 3.3 times lower FIC level when compared to products from _cv_. Ismena with yellow flesh. This can be linked to the properties of polyphenic compounds, including anthocyanins, that might prevent the formation of Maillard reaction products during thermal treatment [27]. In other words, the advanced Maillard reactions in the purple-colored crisps were less intense than in the yellow-colored crisps. Blanching applied before frying significantly diminished the FIC levels in crisps produced from both _cv_. Ismena and Provita. On average, the FIC levels in crisps, regardless of the time and temperature of blanching and frying, were 36% and 43% lower in crisps made from _cv_. Ismena and Provita, respectively, when compared to the level in the control samples (non-blanched). The blanching, as well as its duration, reduced the level of fluorescent intermediary compounds in the crisps. This could be connected with the effect of partial removal of the reducing sugars from the surface of the potato slices during blanching, which might reduce the amount of substrates involved in the Maillard reactions. As a result, this process might halt the formation of fluorescence intermediary compounds in potato crisps. When the crisps from both cultivars were compared, the FIC levels were lower in products gained from _cv_. Provita. This strongly showed that the higher the polyphenol content, the less likely the formation of Maillard reaction products during thermal treatment. Similar to the control samples, crisps fried at higher temperatures were characterized by a higher level of FIC, which was also observed by [PERSON] et al. [28]. One of the most common indicators of non-enzymatic browning reaction that occurs in sugar-rich products is the browning index. In processed foods, browning is linked to the formation of melanoidins--compounds that are formed during the final stage of the Maillard reaction [29]. In the current study, the values of browning index were influenced by the frying temperature of non-blanched samples. The browning index was higher for products from _cv_. Provita with purple flesh when compared to samples from _cv_. Ismena, regardless of the wavelength used for their determination (Table 6). This might be connected with the presence of components that are present in a raw, non-processed purple-fleshed potato and at the maximum absorption wavelength of 420 nm, e.g., selected polyphenols and their complexes [30]. The application of blanching before frying led to a decrease in the BI values (420 nm) of, on average, 61% and 32% for _cv_. Ismena and _cv_. Provita, respectively. Blanching of potato slices in water might result in a partial dissolution of anthocyanins in water. Such a pre-treatment method probably mitigated the course of color reactions during thermal treatment. It was observed that the browning index also decreased with the increase of the temperature and the duration of blanching. A similar relationship was observed in the studies of [PERSON] and [PERSON] [31]. It can be concluded that blanching applied before frying of potato crisps significantly modified the initial chemical composition of potato slices, which influenced the formation of browning pigments in the final products.