Effect of nisin on heat injury and inactivation of Salmonella enteritidis PT4

The ability of heat injury to confer sensitivity to nisin in a Gram negative pathogen was investigated. Injury and inactivation kinetics of Salmonella enteritidis PT4 in the presence of nisin were determined in media, liquid whole egg and egg white using cultural methods and capacitance monitoring to detect injury. Addition of nisin in concentrations from 500 IU/ml to 2500 IU/ml in the heating menstruum caused a reduction of required pasteurisation time of up to 35%, principally as a result of its effect on cells suffering damage during heating. In egg white and liquid whole egg the organismʹs heat susceptibility was greater than in nutrient broth, particularly in egg white which contained no fat and had an alkaline pH. The effect of nisin on heat susceptibility was however less pronounced than in nutrient broth due to its interaction with protein and fat. Though nisin did not enhance the lethality of heat processes, injury is more severe in egg white containing nisin, presumably as a result of its interaction with antimicrobial factors in egg white.