The effects of grapefruit seed extract on the thermal inactivation of Listeria monocytogenes in sous-vide processed doner kebabs

The heat resistance (57.5-65 degrees C) of Listeria monocytogenes in vacuum packaged, cook-in-bag, doner kebabs that included 0.5 or 1% grapefruit seed extract (GSE) was determined. The packages were processed to an internal temperature of 57.5, 60, 62.5 or 65 degrees C in 1 h, held for a predetermined period of time, and then, ice chilled. The surviving cell population was determined by plating diluted samples onto tryptic soy agar overlaid with 10 ml of modified Oxford agar. Survivor curves were fitted to an equation based on the Weibull distribution using the USDA Integrated Pathogen Modeling Program 2013 software tool. The Weibull model consistently offered more accurate fit to all survivor curves based on the smaller root mean square error ( < 0.46). The times to 4-log reduction were 140, 62.38, 14.45 and 6.84 min at 57.5, 60, 62.5, and 65 degrees C, respectively. Supplementing doner kebab with 0.5-1% GSE rendered the pathogen more sensitive to the lethal effect of heat. The results provide the food industry with an option to supplement 0.5-1% GSE in sous vide processed doner kebab, that ensures adequate degree of protection against L. monocytogenes and at the same time, provide energy conservation and quality products.