Effect of Grapefruit Seed Extract on Thermal Inactivation of Listeria monocytogenes during Sous-Vide Processing of Two Marinated Mexican Meat Entrées

Evaluating the Safety of Sous-Vide Cooking for Beef Products Inoculated with Single Strains of Salmonella enterica and Escherichia coli O157

Sous-videcooking is a growing trend among retailers and consumers. Foodborne pathogens may survive the cooking if nonvalidated parameters are used or if pathogens have enhanced thermalresistance. Pathogen inactivation from sous-vide cooking was determined when introduced directly to beef products or via contaminated spices, and with or without a finishing step. Beef products (ground beef, tenderized, and nontenderized steaks) were inoculated with pathogens (Salmonella Montevideo and Escherichia coli O157:NM) in three ways: 1) directly onto the meat 2) ground black pepper incorporated into the recipe 3) ground pepper equilibrated at 30% RH (4 d) prior to incorporation. Beef samples were vacuum-packaged and submerged in a 62.5°C water bath for 120 min. Samples were sampled at 5, 10, 20, and 120 min (recommended from a partner quality study), and a duplicate was grilled to a specific internal temperature (74°C for ground beef, 57°C for steaks) and sampled. Sous-vide cooking reduced pathogen populations by >5 log CFU/g after most treatment times, but less than grilled counterparts (ca. 1-2 log CFU/g difference; p < 0.05).There were no statistically significant differences between inoculation methods, but the tenderization of steaks resulted in significantly lower reductions of pathogens from sous-vide cooking (p < 0.05). Thisresearch challenged sous-vide cooking parameters (120 min, 62.5°C). It showed sous-vide alone lowered pathogens by >4 log CFU/g after most 20-min treatments, but 120-min sous-vide treatments or grilling would be needed for >5-log reductions.Contaminated pepper led to less consistent reductions during the cooking process, yet 2-h sous-vide still achieved a 5-log reduction. Sous-vide cooking instructions must be validated as more products and recipes are marketed.

Optimizing the effects of nisin and nacl to thermal inactivate listeria monocytogenes in ground beef with chipotle sauce during sous-vide processing

Mild cooking thermal treatments, like sous-vide, can compromise ground meat entrees such as meatballs with chipotle sauce, especially when salt levels are reduced during its preparation. Listeria monocytogenes is a thermoresistant pathogen that can be in ready-to-eat food. On the other hand, nisin, due to its thermal stability, can be a good alternative to aid on the thermal inactivation of L. monocytogenes and ensure meat safety. The objective was to optimize the amount of nisin and salt concentrations to thermally inactivate L. monocytogenes during the sous-vide cooking of ground beef marinated in chipotle sauce, and to generate a predictive model. A four-strain cocktail was prepared and inoculated in ground beef in combination (3:2) with chipotle sauce added with nisin (0-150 IU) and salt (0-2%). After that, meat samples were sous-vide cooked at different temperatures, nisin, and salt concentrations, established by a central composite design. Depending on the levels of these factors, D-values ranged from 49.71 to 0.27 min. A predictive model (p < 0.05) was obtained by response surface, which described that D-values variation was explained by the linear effects of the three factors, the interaction between nisin and temperature, and the quadratic effects of salt and temperature. It was also observed that nisin presented a bactericidal effect while salt presented a protective effect during the thermal inactivation of L. monocytogenes. Adding 120 IU of nisin and 0.4% of salt to the meat product at 63°C temperature can help to ensure food safety by making L. monocytogenes cells more sensitive to the lethal effect of heat. The model developed in this study can be used by food processors for planning and designing effective levels of salt and nisin to thermally inactivate L. monocytogenes in ground beef products marinated with chipotle sauce to ensure their safety.

Thermal inactivation kinetics of uropathogenic Escherichia coli in sous-vide processed chicken breast

Chicken is a suspected reservoir of uropathogenic Escherichia coli (UPEC), resulting in foodborne urinary tract infections (UTIs). Sous-vide ready-to-eat (RTE) food products may be associated with microbial hazards due to the low-temperature long-time (LTLT) process. However, little is known regarding the survival of UPEC during sous-vide cooking. The aim of this study was to evaluate the heat resistance of UPEC in chicken breast during sous-vide processing and establish predictive inactivation models. Chicken breast samples were inoculated with a four-strain cocktail of UPEC, including reference strains from UTI patients and chicken isolates. The inoculated samples, with or without 3% NaCl solution for marination, were vacuum sealed in bags, immersed in a temperature-controlled water bath, and cooked at 50 °C, 55 °C, 60 °C, and 63 °C. The change in survival of populations of UPEC was fitted with the linear and Weibull inactivation models to obtain the survival curves at different temperatures; the D- and z-values were also calculated. The goodness-of-fit was evaluated using the root mean square error (RMSE), sum of squared errors (SSE), adjusted R², and Akaike information criterion (AIC). The results showed that the linear model with tail was better than the Weibull model in terms of fitting performance. With the addition of salt marinade, D-values at 50 °C, 55 °C, 60 °C, and 63 °C determined by the linear model with tail decreased from 299.78 to 166.93 min, 16,60 to 13.87 min, 4.06 to 3.05 min, and 1.05 to 0.87 min, respectively, compared with the controls. The z-values of control and salt-marinated samples were 6.14 °C and 5.89 °C, respectively. The model developed for predicting UPEC survival under sous-vide cooking was validated using an additional survival curve at 58 °C. The validation results showed that the RMSE was 0.122 and 0.133 log CFU/g, and the proportion of relative error was 0.875 and 0.750 in the acceptable prediction zones for the control and salt-marinated samples, respectively. In conclusion, the heat resistance of an emerging foodborne pathogen, UPEC, in sous-vide processed chicken breast was revealed for the first time. Our results showed that salt marinade (3% NaCl) increases the heat sensitivity of UPEC during the sous-vide processing. The developed survival functions based on the linear model with tail can be applied to control the thermal lethality of UPEC.

Increased thermal sensitivity of Listeria monocytogenes in sous-vide salmon by oregano essential oil and citric acid

Inadequate cooking during sous-vide processing may cause foodborne diseases in case the food is contaminated with pathogens such as Listeria monocytogenes. In this study, thermal inactivation of L. monocytogenes in sous-vide processed salmon was investigated. Oregano oil and citric acid were used alone or in combination to determine the probability of increasing the efficiency of heat treatment. Control (C); 0.5% citric acid added (S); 1% oregano essential oil added (O); and citric acid and oregano essential oil combined (OS) groups were prepared. Samples were inoculated with L. monocytogenes, vacuum packed, then sous-vide cooked at 55, 57.5, 60, or 62.5 °C for predetermined times. The D-values of all treated samples were significantly lower than control. The use of oregano oil (O), citric acid (S) and their combination (OS) significantly reduced the time required to inactivate L. monocytogenes. The z-values of L. monocytogenes in C, O, S and OS groups were 5.50, 5.62, 6.54, and 6.92 °C, respectively. It was determined that effective results could be achieved by adding natural antimicrobials to provide safety in sous-vide fish.