Fate of lysostaphin in milk from individual cows through pasteurization and cheesemaking1

• Published in: Journal of dairy science 2009-02, Vol.92 (2), p.444-457
• Main Authors: Van Hekken, D.L., Wall, R.J., Somkuti, G.A., Powell, M.A., Tunick, M.H., Tomasula, P.M.
• Format: Article
• Language: English
• Subjects: lysostaphin; milk; processing; transgenic cow
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2008-1019

Transgenic cows secreting over 3μg of lysostaphin/ mL of milk are protected against mastitis caused by Staphylococcus aureus, but it is unknown if active lysostaphin persists through dairy processing procedures or affects 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 heat treated at 63°C for 30min, 72°C for 15s (high temperature, short time), or 140°C for 2s (UHT). Portions of the high temperature, short-time 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 cheesemaking. Based on the amount of lysostaphin present in the starting cheesemilk, 10 to 15% of the lysostaphin was recovered in the whey, 21 to 55% in the cheese curd at d 1, and 21 to 36% in cheese stored at 4°C for 90 d. Enough of the lysostaphin secreted into milk by transgenic cows survived typical dairy processing conditions to impart potential value as a bioprotective agent against staphylococci in dairy foods.