Abstract: Plasmin is an important factor affecting the shelf-life quality of milk products, and its hydrolytic activity is regulated by many factors, such as activators, inhibitors, and activator inhibitors. Compared with protease secreted by psychrophilic bacteria, plasmin presents different thermal inactivation parameters and hydrolysis properties; the milk gelation properties induced by the two enzymes, the gelation mechanisms and the methods used to detect the milk hydrolysates are different. Plasmin activity in raw milk is affected by dairy cow breeds, lactation stage, parity, and the number of somatic cells, as well as protease secreted by bacteria. As whey protein, casein and Maillard reaction can affect plasmin structure and substrate recognition by it, heating, membrane filtration, and high pressure processing can affect plasmin activity. In this paper, we summarize the composition and regulatory mechanism of the plasmin system in milk, the mechanism of plasmin-induced age gelation of milk, the factors affecting plasmin activity and the methods used to assay plasmin activity, with the aim to provide a reference for further research on milk plasmin.

Key words: milk; plasmin; age gelation; cows; processing