Effect of heat treatment on Listeria monocytogenes and gram-negative bacteria in sheep, cow and goat milks.

Sheep milk, compared with cow and goat milk, had a protective effect on Gram-negative bacteria and Listeria spp. heated at 65 degrees C in a test-tube method. This effect was not solely due to fat content as cow milk artificially reconstituted to 10% homologous fat was not as protective. Listeria monocytogenes in whole sheep, cow and goat milks at an inoculum level of 1 x 10(6) cfu ml-1 was heated at 68 degrees C for 15 s in the plate pasteurizer and survival was only detected in whole sheep milk after heating. Whole sheep, cow and goat milks containing high levels of L. monocytogenes (1 x 10(6) cfu ml-1) could not survive the current HTST plate pasteurization protocol.