## 3 Results and Discussion
### Microbiological Quality and Biological Activity of Fermented OBB  
In the second part of the presented work, oat fermented beverages were produced with the addition of selected fruit extracts and lyophilistes and chosen LAB strains. Oat was chosen as a fermentation matrix due to its good nutritional properties including,among others, soluble fibre, essential amino acids, vitamins, minerals, and unsaturated fatty acids. Due to its pro-health and nutritional value [10; 15], it could gain acceptance by consumers. The addition of fruit extracts of lyophilates was proposed to increase the polyphenol content and antioxidant activity, enhancing health-promoting properties. It is worth underlining that the availability of similar products on the market, which could be substitutes for fermented milk products, is still limited, although the group of consumers interested in such a solution is growing. Based on the results from the first part of this study, chokeberry as well as hawthorn extracts and freeze-dried fruits were chosen due to their high antioxidant properties and antibacterial activity towards pathogenic bacteria as the additives to the prepared oat fermented beverage. The choice of chokeberry preparations was due to its high content of polyphenolic compounds and antioxidant potential, also confirmed in the literature as a material with extremely high biological potential [27]. Although blueberry extracts and lyophilates demonstrated a higher antioxidant activity than hawthorn, their antibacterial properties were similar to hawthorn in the case of extracts and weaker than hawthorn in the case of lyophilates. Moreover, hawthorn is used much less frequently than blueberry; therefore, it is more interesting to use it as an additive to design oat fermented beverages. As hawthorn is one of the oldest known medicinal plants in Europe and presents different pro-health properties such as neuroprotective, hepatoprotective, or cardioprotective effects, an increase in interest in using this plant in food applications including yogurts and tonic wines is observed [67; 68; 69]. In turn, _L. plantarum_ was chosen as a starter culture due to its low sensitivity to the extracts and lyophilate activity, which suggests that its growth would not be inhibited in the prepared oat beverages with fruit additives. The addition of chokeberry extract and lyophilate (in amounts of 1% and 5%) significantly increased the TPC in oat beverages both immediately after application and after 20 h of fermentation compared to control samples (without any addition). The results are presented in Table 4. The increase in TPC at 0 h of fermentation was 132.04 and 120.83 mg GAE/L in samples with the 1% addition in comparison with the control, while in samples with the 5% addition, it was 130.76 and 158.01 mg GAE/L for the chokeberry extract and lyophilate, respectively. After 20 h of fermentation, it was noticed that the TPC decreased both in control samples and in oat beverages with the addition of chokeberry extract and lyophilate. However, a significant decrease in TPC was observed only in control samples (decrease from 84.93 to 64.92 mg GAE/L) and samples with the 5% addition of chokeberry lyophilate (decrease from 242.94 to 213.71 mg GAE/L). Comparing the TPC values in oat drinks depending on the amount of additive (1% and 5%) as well as on the type of additive (extract/lyophilisate) and fermentation time (0 h and 20 h), no significant differences were noticed, except for the 5% addition of chokeberry lyophilate in 0 h of fermentation where the TPC content was significantly higher than those of the other variants. The antioxidant activity of the prepared oat drinks was significantly higher compared to control samples only in the case of the 5% addition of chokeberry extract (0.792 mM) as well as 1 and 5% additions of chokeberry lyophilate (0.750 and 0.847 mM, respectively) immediately after application (at 0 h of fermentation).