Measuring the Activity of Native Plasmin Enzyme in Milk and Milk Sources

Abstract. During the casein hydrolysis that occurs as hard cheese ripens, plasmin can alter the properties of the casein network, the ripening rate, and the texture of the final product. This research featured a model mixture of micellar casein concentrate, high-scald cheese curd, and whey. Spectrophotometry was used to determine the activity of the native plasmin–plasminogen enzyme system, as well as the effect of these enzymes on cheese curd proteolysis. The plasmin activity in the micellar casein concentrate and the experimental cheese sample was higher than that of the control sample on the third day of ripening. By the end of the ripening period, the experimental cheese demonstrated a decrease in enzyme activity, indicating the release of amino acids from peptides, while the enzyme remained bound to the protein matrix and did not migrate into the whey. The rate of amino acid release in the cheese with micellar casein concentrate was 1.35 times higher, potentially allowing for a 20% reduction in cheese ripening time. Spectrophotometry proved effective in monitoring the plasmin–plasminogen enzyme system activity in cheesemaking, making it possible to achieve target technological parameters and optimize production processes.