## 1 Introduction  
Currently, consumers are increasingly paying attention to the quality of consumed products, especially to their health value. Fermented milk products, mainly yogurts, have been gaining in popularity recently [1, 2]. Due to its high nutritional value and excellent therapeutic and sensory properties, yogurt is one of the oldest and most popular fermented milk products consumed worldwide [34]. It should be emphasized that the fermentation process carried out using lactic acid bacteria is accompanied by a release of bioactive peptides and free amino acids with various biological activity, including antioxidant effects, from milk proteins [5, 6, 7]. Although the beneficial properties of yogurt have long been known, scientists are constantly trying to improve its functional properties and provide new yogurt-based products that will be attractive to consumers [8, 9, 10]. Research in this field is focused on the enhancement of the antioxidant activity of manufactured products with the maintenance of an appropriate flavor and aroma profile [7, 11, 12]. Products being a rich source of antioxidants positively affect the antioxidant status of the organism. Therefore, such products are able to reduce the risk of development of many lifestyle diseases. It also increases the overall resistance of the organism to diseases and infections, slows down the process of organism aging, and reduces the frequency of neurological diseases, e.g., Parkinson's and Alzheimer's diseases or cerebral ischemia [1; 3; 5; 6]. Numerous studies indicate that the antioxidant status of dairy products can be modified with the use of natural plant materials (fruits, vegetables, herbs) exhibiting high content of phenolic compounds and carotenoids in the production process [13; 14; 15; 16]. Additionally, these additives have an impact on the sensory traits of the final product and contribute to an extension of the product shelf life via inhibition of the lipid oxidation process during refrigerated storage [12; 17; 18; 19]. It should be emphasized that the bacterial cultures used exert a substantial impact on the antioxidant potential value. As indicated in many studies, fermented products containing probiotic strains are characterized by substantially increased antioxidant activity [3; 7; 11]. The level of the antioxidant status of milk used as a raw material for the dairy industry can be modified with the use of natural additives in cow nutrition. Herbal mixtures or post-production residues provided by the food industry are used most frequently [20; 21; 22; 23].  
In a previous study [20], the authors assessed the effect of the addition of herbal blends to the feed ration for Holstein-Friesian cows on the level of antioxidant potential of milk. It was shown that the use of the herbal additive significantly increased the antioxidant potential of milk. From the nutritional point of view, this seems to be particularly important for the protection of the organism against the harmful effects of oxidative stress. To meet the expectations of modern consumers, the present research was undertaken to assess the potential of milk of herbal blend-fed cows to be used for the production of yogurts characterized by increased antioxidant potential with regard to the duration of storage of the products.