Thermal inactivation of Salmonella Typhimurium and surrogate Enterococcus faecium in mash broiler feed in a laboratory scale circulated thermal bath

Abstract

ABSTRACT: This study compares kinetic parameters of Salmonella and surrogate Enterococcus faecium in mash broiler feed during thermal inactivation. Two-gram samples of mash broiler feed were added into a filtered sample bag and inoculated with nalidixic acid (NaL, 200 ppm) resistant S. Typhimurium or Enterococcus faecium, followed by vacuum-packaging and heating in a circulated thermal water bath at 75°, 85°, and 95°C for 0 to 180 s. Counts of bacterial survival were analyzed on tryptic soy agar and bile esculin agar plus 200 ppm of NaL. Microbial data and thermal kinetic parameters (n = 8, Global-Fit and United States Department of Agriculture [USDA]-Integrated-Predictive-Modeling-Program software) were analyzed by JMP software. Heating mash broiler feed at 75°, 85°, and 95°C decreased (P 6 log10CFU/g after 180, 60, and 50 s, respectively. Heating E. faecium in feed at 75°, 85°, and 95°C for 180, 120, and 70 s achieved reductions of 3, 6, and >6.5 log10CFU/g, respectively. D-values of linear, Weibull models, and z-value of Salmonella at 75°, 85°, and 95°C were 1.8 to 11.2, 4.2 to 21.8, and 28.6 s, respectively, which were lower (P < 0.05) than those of E. faecium (3.7–18.1, 8.5–34.4, and 34.1 s). Linear with Tail, Linear with Tail and Shoulder, and Weibull with tail equations revealed that E. faecium were more resistant (P < 0.05) to heat than Salmonella as shown by longer “Shoulder-time” (26.5 vs. 16.2 s) and greater “Tail” effect (4.4–4.5 vs. 2.5–2.6 log10CFU/g). Results clearly suggested that E. faecium can be used as a surrogate for Salmonella to validate thermal inactivation during feed manufacture.

Keywords

• broiler feed
• Salmonella
• Enterococcus faecium
• thermal inactivation
• surrogate bacteria