###### Abstract  
The aim of the study was to apply the bioactive components casein hydrolysate and casein-iron chelate to yoghurt and to analyze their influence on product parameters. Casein was hydrolyzed with the non-commercial protease obtained from _Yarroviia lipolytica_ yeast and subjected to chelating process with Fe\({}^{2+}\) ions. Both preparations were introduced to yoghurt production as additives for elevation of dry matter by 2%. The control yoghurt was produced with the addition of skim milk powder. In the prepared experimental yoghurts, the content of dry matter [DM] protein, fat, as well as iron contents were determined. The conducted studies showed that in all analyzed yogurts, DM content was at a similar level, while the protein content was significantly (\(p<0.05\)) higher in the variant containing 2% casein-iron chelate. In yoghurts with the casein-iron chelate as a bioactive compound, the iron concentration was about 61.5-123 times higher than in yoghurt with the addition of skim milk powder. It was shown that during storage the addition of casein-iron chelate positively influenced the number of analyzed microbe groups. bioactive compounds; yoghurt; casein-iron chelate; yoghurt microflora +
Footnote †: This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ([[https://creativecommons.org/licenses/py/4.0/](https://creativecommons.org/licenses/py/4.0/)]([https://creativecommons.org/licenses/py/4.0/](https://creativecommons.org/licenses/py/4.0/))). Footnote †: This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons. Yoghurt is a valuable source of calcium and protein, although it is deficient in iron. People whose diets are based on dairy products for a long time are at risk of developing so-called \"milk anaemia\". The groups most often exposed to this disorder are children at the ages of 1 to 3 years, because the stock of hematopoietic components stored in the liver decreases after infancy [9; 10]. Yoghurt as a popular dairy product can be an appropriate carrier for iron supplementation due to the properties of the main milk protein, casein, a phosphoprotein with metal ions binding ability. Casein and its hydrolysates show various biological activities, including the natural ability to chelate metals, positively influencing the immune system [11; 12]. These properties are determined by strong polar anionic sequences consisting of three phosphoserine residues and two glutamic acid residues. Caseinophosphopeptides (CPPs), formed during the hydrolysis of \(\alpha\)s1, \(\alpha\)s2, and \(\beta\) casein, help to achieve and maintain mineral homeostasis [13]. They are resistant to proteolytic enzymes present in the human gastrointestinal tract, keep the chelated minerals dissolved, and prevent their precipitation. Therefore, these elements are better absorbed. Based on the already known health beneficial properties of yoghurts, as a source of bioactive compounds, it is possible to combine additional enrichment with health-promoting bioactive ingredients and to create additional functionality [8]. One of the methods of yoghurt enrichment with iron is the addition of natural bioactive substances that do not change the quality characteristics of the final product but constitute an additional source of iron in the daily diet. Application of iron in the form of casein-iron chelate used for the elevation of dry matter, can be an effective way to increase iron intake in the population's diet. The absorption of iron in the form of a peptide chelate is much higher in comparison to its inorganic salts. Chelates are more resistant to absorption inhibitors. Other aspects that should be taken into account are the smell and taste of a product as some iron compounds may cause a metallic aftertaste in food, deemed unacceptable by consumers.