Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/29/2008
Publication Date: 2/2/2009
Citation: Van Hekken, D.L., Wall, R.J., Somkuti, G.A., Powell, A.M., Tunick, M.H., Tomasula, P.M. 2009. Fate of lysostaphin in milk from individual cows through pasteurization and cheesemaking. Journal of Dairy Science. 92:444-457. Interpretive Summary: Udder infections cost the dairy industry billions of dollars each year in reduced milk yields and poor animal health with Staphylococcus aureus causing a third of all the infections. Transgenic cows that secrete very small amounts of the bacteriolytic enzyme lysostaphin in their milk are resistant to infections caused by S. aureus. The fate of the lysostaphin in milk processed into dairy products is unknown. This study shows that lysostaphin persists throughout typical milk pasteurization and cheesemaking conditions and remains active in the finished dairy products.
Technical Abstract: Transgenic cows secreting over 3-ug lysostaphin/mL milk are protected against mastitis caused by Staphylococcus aureus, but it is unknown if active lysostaphin persists through dairy processing procedures or impacts the production of fermented dairy foods. The objective of this study was to determine the fate of lysostaphin as milk was pasteurized and then processed into cheese. Raw milk from transgenic cows was either heat treated at 63C for 30 min, 72C for 15 s (high temperature short time, HTST), or 140C for 2 s (ultra high temperature, UHT). Portions of the HTST milk were manufactured into semi-hard cheeses. Aliquots taken at each processing step were assayed to determine the quantity (ELISA) and activity (ability to inhibit S. aureus growth) of lysostaphin. Results indicated that most of the lysostaphin was present in the aqueous portion of the milk and was not affected by pasteurization although UHT treatment reduced enzyme concentration by 60%. The quantity and activity of the lysostaphin decreased during cheese making. Based on the amount of lysostaphin present in the starting cheesemilk, 10 to 15% of the lysostaphin was recovered in the whey and 21 to 55% in the cheese curd at day 1, with 21 to 36% remaining in cheese stored at 4 deg C for 90 days. The potential value of lysostaphin as a bioprotective agent against staphylococci in dairy foods and its impact on food quality remains to be determined.