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 ne gative 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 capa citance monitoring to detect injury. Addition of nisin in concentratio ns from 500 IU/ml to 2500 IU/ml in the heating mellstruum caused a red uction 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 organism's heat susceptibility was grea ter than in nutrient broth, particularly in egg white which contained no fat and had an alkaline pH. The effect of nisin on heat susceptibil ity was however less pronounced than in nutrient broth due to its inte raction with protein and fat. Though nisin did not enhance the lethali ty of heat processes, injury is more severe in egg white containing ni sin, presumably as a result of its interaction with antimicrobial fact ors in egg white. (C) 1998 Elsevier Science B.V. All rights reserved.