Study of Listeria monocytogenes survival during the preparation and the conservation of two kinds of dairy product.

: We tested yoghurts and soft cheeses for survival of Listeria monocytogenes during their manufacture and their storage at 4 degrees C. In yoghurt, even when the concentration of germs is high, the bacterial population decreased rapidly and the life of time of L. monocytogenes in this product depends on the sample acidity. The microorganisms disappear when the pH falls to 3.5. In soft white cheeses, only a fabrication with chemical and bacterial ferments allows an acidity which is compatible with destruction of majority of L. monocytogenes. Under these conditions, the pH decreases to 4-4.5 according to the series of production.