Determination of the effect of milk fat on the inactivation of Listeria monocytogenes by ohmic heating

Abstract

Research in recent years has focused on innovative technologies that provide pathogen inactivation without damaging the structural properties of foods. Ohmic heating (OH) is an innovative technology, that provides an effective microbial inactivation with massive and rapid heating. This study aims to determine the effects of milk fat on the inactivation of Listeria monocytogenes by OH with a low voltage gradient. L. monocytogenes (ATCC 13932) inoculated 3.1%, 1.5%, and 0.1% fat-milk samples were heated up to 62°C by OH and conventional heating (CH) process. OH treatment lead to the inactivation of L. monocytogenes in both 1.5% and 0.1% groups and led to approximately 5.30 log decrease, however, there was a 3.10 log decrease in the 3.1% group at 6 min. CH lead to a few reduction as 0.21, 0.29 and 0.39 log in 3.1%, 1.5% and 0.1% fat-milk respectively. In OH, the sublethal injury ratio was higher than CH in all milk groups. However, OH did not statistically change color and pH values at the 6th min of the process, had a significant effect on hydroxymethylfurfural value only in 3.1% fat-milk. In conclusion, the increased fat content may have important inhibitory effects on pathogen inactivation in OH. Thus, the OH conditions should be chosen carefully to sufficient inactivation of pathogens in milk with high-fat content.