Proteolysis in UHT milk can be caused by PL and heat resistant proteases from, e.g., psychotropic bacteria. The milk used in this study was one day old low-pasteurised milk, which makes it unlikely that the extensive proteolysis in Milk72 was caused by bacterial proteases. The appearance of proteose peptones and -caseins suggested that PL was the main actor of proteolysis. Bacterial proteases are more unspecific in their cleavage sites and are capable of hydrolysing -casein (Datta & Deeth, 2001). In Milk72 and Milk95 no proteolysis of -casein was observed, further
strengthening the indications that PL was the main active protease in Milk72.