Combined Effect of High Pressure and Temperature on Inactivation and Injury of Listeria monocytogenes In UHT Whole Milk

Abstract

Listeria monocytogenes is a Gram positive, psychrotrophic microorganism that can grow even at -0.4C. As L. monocytogenes is capable of growing at refrigeration temperature, it is a potential threat for stored foods such as milk and dairy products. The microorganism shows barotolerance when treated with high pressure in milk. In the present study, inactivation and injury of L. monocytogenes was evaluated under the combined effect of high pressure and temperature in UHT whole milk. The milk samples were treated at two pressure levels (500 and 600 MPa) and 43C for different treatment times. Stationary phase cells grown at 43C, documented to be most resistant, were used for experiments. After the high pressure treatment, the milk samples were serially diluted and spiral plated on Tryptic Soy Yeast Extract Agar (TSAYE) and Modified Oxford Agar (MOX).