Bovine plasminogen activation by free fatty acids in milk and simple detection of plasminogen activators using milk agar plates.

Plasminogen is an inactive protease in milk, which can be activated to plasmin. Whole milk contains fat and in response to lipase activity, free fatty acids are released. Free fatty acids are not known to act as an activator for plasminogen. The aim of this study was to determine whether commercial bovine plasminogen could be activated to plasmin by commercial free fatty acids present in milk, and also to determine if plasminogen activators to plasmin are present in abnormal milk using milk agar plates and the Merck protease assay. Fatty acids and activators present in abnormal milk had the ability to activate plasminogen to plasmin, which could, after weeks, harm milk protein stability during extended storage time (ultra-high temperature milk). The milk agar plate technique containing plasminogen could detect plasmin activators present in abnormal milk. This can act as an indicator of high-risk milk being used within the ultra-high temperature milk industry.