## 4 Discussion
used convection-dried raspberry and blueberry pomace to enrich gluten-free cookies. They also confirmed that, in comparison to control wafers, the TPC content and antioxidant activity of samples containing pomace were significantly improved. However, they noted that the blueberry pomace-enriched product contained up to six times more polyphenols than that fortified with raspberry pomace [35]. In the present study, besides ethanol extracts, buffer extracts were prepared and simulated in vitro digestion was performed. The idea was to determine the amount of polyphenols present in fortified wafers that can constitute potentially bioavailable fractions. Bioaccessibility is defined as the amount of compounds released from their matrix in the gastrointestinal tract available for the intestinal absorption [37; 38]. In the gastrointestinal tract, phenolics are released from the food matrix by direct solubilization in the intestinal fluids and through the action of digestive enzymes. In other words, not only does the total content of phenolic compounds have to be taken into account, but also the interactions of matrix components that can significantly affect the amount of polyphenols that can be released from the product in the gastrointestinal tract. The results indicate that the concentration of polyphenols after simulated digestion of wafers with 10-30% pomace was between 4.8 and 2.4 times higher than in the ethanol extracts. With the higher addition, the differences were much smaller, which may indicate an antagonistic interaction between phenolic compounds and the other ingredients (especially fiber) of the wafer dough influencing the potential bioavailability of polyphenols. The lower proportional bioavailability of polyphenols from the RP-50 and RP-75 wafers (i.e., the smaller difference between the EtOH and DIG extracts) may be related to the higher content of dietary fiber that traps bioactive compounds and makes them less accessible to enzymes, hindering their release; therefore, most of them reach the colon intact. However, as reported earlier, this does not make this type of food less beneficial. It has been shown that these compounds can be used by intestinal microflora, demonstrating prebiotic properties and meeting the demand for pro-health antioxidants in the large intestine [17; 39; 40]. This can be a vital tip for potential producers and nutritionists. [PERSON] et al. (2017) prepared cookies with substitution of 56% of wheat flour with dried blueberry pomace and concluded that the supplemented cookies had highly increased values of antioxidant capacity and polyphenol content, compared with control cookies. These results are in agreement with our studies. They also subjected the cakes to in vitro digestion and found that that 35% of the extractable and hydrolysate phenols are bioaccessible [41]. The process of simulated digestion contributes to the release of potentially bioavailable phenolic compounds from the food matrix showing the ability to inhibit the activity of the LOX and COX-2 enzymes involved in the metabolism of arachidonic acid, from which highly reactive pro-inflammatory compounds, i.e., prostaglandandins and leukotrienes, can be generated. Such activity of phenolic compounds, especially those from the group of flavonoids, has been confirmed in the literature [42; 43]. Polyphenols present in raspberry pomace are also effective inhibitors of XO, which catalyzes the conversion of hypoxanthine to xanthine and xanthine to uric acid, with concomitant production of hydrogen peroxide and superoxide anions as by-products, which may contribute to intensification of inflammation. The interaction of free radicals with cellular components may result in damage to cells and tissues, and this may contribute to aggravation of inflammation [44]. Numerous in vitro studies have confirmed that anthocyanins show different degrees of COX-2 inhibition depending on the amount of free OH [44; 45; 46].