## 1 Introduction
Cornelian cherry fruits are oval to pear-shaped, and their color ranges from red to purple [20]. Cornelian cherry is a good source of vitamin C, ranging from 29 to 300 mg per 100 g of fresh weight--significantly higher than that of strawberry and kiwi fruit, which contain between 29 and 80 mg per 100 g [21; 22]. It is also particularly rich in potassium (approximately 1490 mg/100 g), as well as other minerals such as zinc, manganese and iron [23]. Additionally, this fruit is a source of various phytocompounds, including anthocyanins, phenolic acids, flavonoids, tannins, catechins (elagoic acid, epicatechnia, catechin and chlorogenic acid), as well as caffe acid and iridoids --many of which have documented anti-inflammatory and antioxidant properties [24]. Numerous studies have demonstrated that, due to its high phenolic content, cornelian cherry exhibits strong radical scavenging activity [25; 26] and has antioxidant, anti-inflammatory, anti-parasitic, anti-cancer and protective effects on the cardiovascular system, liver, and kidneys [27; 28; 29; 30; 31]. Previous studies on the addition of fresh or processed fruits to yogurts have shown that this is a commonly used strategy to increase the content of phenolic compounds in the product [32]. Phenolic compounds are natural substances with strong antioxidant properties that can contribute to enhancing the health-promoting qualities of yogurts [33]. Enriching yogurt with fruits not only increases its nutritional value, but also positively affects its antioxidant properties, which is particularly important in protecting the body against oxidative stress. [PERSON] et al. [34] showed that the addition of fruit extracts rich in polyphenols to yogurt beverages improved their antioxidant activity. Research into the functional properties of yogurt, including its antioxidant activity, is an important topic in the scientific literature. However, studies focusing specifically on the impact of fruit addition on the antioxidant activity and health-related properties of ready-to-eat natural yogurt remain relatively scarce. Therefore, further research in this area is warranted. To our knowledge, no published study has evaluated the antioxidant activity of yogurts containing a wide variety of fruit additions in a single study. Such investigations can provide valuable insights useful for the development of functional dairy products and offer a comprehensive understanding of their antioxidant potential, which is crucial not only for product quality but also for consumer health benefits. There are many fruit-containing yogurts on the market; however, the fruits in commercial yogurts are usually processed, e.g., pasteurized. Fruit yogurts can easily be prepared at home by mixing natural yogurt with fresh or thawed fruits. When consumed immediately after preparation, such yogurts offer a pronounced fruit flavor without added sugars. Nevertheless, questions arise as to whether the addition of fruit to natural yogurt truly enhances its antioxidant properties and whether it negatively affects the bacteria present in the yogurt. The aim of this study was to evaluate the antioxidant properties of natural yogurts enriched with thawed fruits (bilberries, cherries and strawberries) and to compare their antioxidant activity with that of commercial yogurts containing the same processed fruits. These particular fruits were selected due to their popularity and availability. Additionally, the impact of fruit addition on the number of yogurt bacteria was assessed. Furthermore, we analyzed the antioxidant properties of yogurts with the added cornelian cherry. Given its high antioxidant potential, we aimed to compare its effects with those of more commonly used fruit additives in yogurt. To the best of our knowledge, this is the first study to analyze the antioxidant properties of yogurt enriched with cornelian cherry.