The interactive effects of heating temperature (55 to 65°C), sodium chloride (NaCl; 0 to 2%), and green tea 60% polyphenol extract (GTPE; 0 to 3%) on the heat resistance of a five-strain mixture of Listeria monocytogenes in ground turkey were determined. Thermal death times were quantified in bags that were submerged in a circulating water bath set at 55, 57, 60, 63, and 65°C. The recovery medium was tryptic soy agar supplemented with 0.6% yeast extract and 1% sodium pyruvate. D-values were analyzed by second-order response surface regression for temperature, NaCl, and GTPE. The data indicated that all three factors interacted to affect the inactivation of the pathogen. The D-values for turkey with no NaCl or GTPE at 55, 57, 60, 63, and 65°C were 36.3, 20.8, 13.2, 4.1, and 2.9 min, respectively. Although NaCl exhibited a concentration-dependent protective effect against heat lethality on L. monocytogenes in turkey, addition of GTPE rendered the pathogen more sensitive to the lethal effect of heat. GTPE levels up to 1.5% interacted with NaCl and reduced the protective effect of NaCl on heat resistance of the pathogen. Food processors can use the predictive model to design an appropriate heat treatment that would inactivate L. monocytogenes in cooked turkey products without adversely affecting the quality of the product.
The objective of the present study was to analyze the combined effect of heat treatment (55 to 62.5 °C) and citral (0 to 3%) on the heat resistance of Escherichia coli O104:H4 inoculated in ground beef. Inoculated meat packages were immersed in a circulating water bath stabilized at 55, 57.5, 60 and 62.5 °C for different times. The surviving microbial cells were counted in tryptic soy agar. A factorial design (4 x 4) was used to analyze the effect and interaction of heat treatment and citral. The results showed that heat and citral promoted E. coli O104:H4 thermal inactivation, suggesting a synergistic effect. At 55 °C, the incorporation of citral at 1, 2 and 3%, decreased D values (control: 42.75 min) by 85, 89, and 91%, respectively ( p < 0.05). Similarly, other evaluated temperatures exhibited a citral concentration-dependent effect ( P < 0.05). In conclusion, the findings could be a valuable tool for the food industry in designing a safe thermal process for inactivating E. coli O104:H4 in ground beef under similar thermal inactivation conditions.
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