Evaluation of Salmonella thermal inactivation model validity for slow cooking of whole-muscle meat roasts in a pilot-scale oven

Process Humidity Affects Salmonella Lethality at the Surface and Core of Impingement-Cooked Meat and Poultry Products

ABSTRACT

Recent revisions to U.S. Department of Agriculture, Food Safety and Inspection Service (FSIS) compliance and safe harbor guidelines for ready-to-eat meat and poultry products addressed process humidity requirements. Given the lack of prior data for impingement-cooked products, the present study was conducted to evaluate the impact of process humidity on Salmonella lethality at the product core and surface and compliance of the results with FSIS lethality performance standards. Whole muscle beef strips, ground beef patties, whole muscle chicken breast fillets, and breaded ground chicken patties were inoculated with an eight-serovar cocktail of Salmonella. Beef and chicken samples were cooked in a pilot-scale moist-air impingement oven to a core temperature of 70.0 and 72.8°C, respectively, immediately quenched in liquid nitrogen, and dissected to obtain core and surface samples. Variables included oven temperature (218 and 232°C), air velocity (0.7 and 2.8 m/s), and oven humidity (0.7, 15, 30, or 70% moisture by volume [%, v/v]). Additional treatments were performed to examine the impact of supplemental critical control processes such as increased endpoint temperature, postoven carryover time, and pre- or postoven steam treatments. Salmonella reductions of >7 log units were reliably achieved in chicken patties regardless of the processing variables; however, none of the treatments reliably ensured >6.5-log reductions of Salmonella in ground beef. A majority of whole-muscle samples failed to meet the required performance lethality when processed at 0.7% (v/v) humidity; however, Salmonella inactivation was significantly improved (P < 0.05) at oven humidities of ≥30% (v/v). Dry oven conditions achieved greater Salmonella lethality at the core than at the surface for multiple products (P < 0.05). The efficacies of minimal and supplemental critical controls were dependent on product, process, and humidity (P < 0.05). Overall, process humidity and product variability should be considered in regulatory requirements and process validations.

HIGHLIGHTS

Multidrug-Resistant Salmonella I 4,[5],12:i:- and Salmonella Infantis Infections Linked to Whole Roasted Pigs from a Single Slaughter and Processing Facility

We describe two outbreaks of multidrug-resistant (MDR) Salmonella I 4,[5],12:i:- infection, occurring in 2015 to 2016, linked to pork products, including whole roaster pigs sold raw from a single Washington slaughter and processing facility (establishment A). Food histories from 80 ill persons were compared with food histories reported in the FoodNet 2006 to 2007 survey of healthy persons from all 10 U.S. FoodNet sites who reported these exposures in the week before interview. Antimicrobial susceptibility testing and whole genome sequencing were conducted on selected clinical, food, and environmental isolates. During 2015, a total of 192 ill persons were identified from five states; among ill persons with available information, 30 (17%) of 180 were hospitalized, and none died. More ill persons than healthy survey respondents consumed pork (74 versus 43%, P < 0.001). Seventeen (23%) of 73 ill persons for which a response was available reported attending an event where whole roaster pig was served in the 7 days before illness onset. All 25 clinical isolates tested from the 2015 outbreak and a subsequent 2016 smaller outbreak (n = 15) linked to establishment A demonstrated MDR. Whole genome sequencing of clinical, environmental, and food isolates (n = 69) collected in both investigations revealed one clade of highly related isolates, supporting epidemiologic and traceback data that establishment A as the source of both outbreaks. These investigations highlight that whole roaster pigs, an uncommon food vehicle for MDR Salmonella I 4,[5],12:i:- outbreaks, will need further attention from food safety researchers and educators for developing science-based consumer guidelines, specifically with a focus on the preparation process.

Comparative Effect of Heat Shock on Survival of O157:H7 and Non-O157 Shiga Toxigenic Escherichia coli and Salmonella in Lean Beef with or without Moisture-Enhancing Ingredients

Thermal tolerance of pathogenic bacteria has been shown to increase after exposure to sublethal elevated temperatures, or heat shock. We evaluated the effect of heat shock at 48°C on thermal tolerance (D_55°C) of cocktails of O157 and non-O157 Shiga toxigenic Escherichia coli (STEC) and Salmonella in lean ground beef with or without moisture-enhancing ingredients. Beef was moisture enhanced to 110% (w) with a 5% NaCl-2.5% sodium tripolyphosphate (w/w) brine. Meat, with or without added brine, was inoculated (∼10⁸ CFU/g) and heat shocked at 48°C for 0, 5, or 30 min, followed by isothermal heating at 55°C. Inoculated control samples were unenhanced and were not subject to heat shock. From the linear portion of the log CFU per gram surviving cells over time plots, D_55°C-values (minutes) were calculated. D_55°C was 20.43, 28.78, and 21.15 min for O157, non-O157, and Salmonella controls, respectively. Overall, heat shock significantly increased D_55°C, regardless of pathogen (P < 0.05). After 30 min of heat shock, D_55°C increased 89 and 160% for O157 STEC, 32 and 49% for non-O157 STEC, and 29 and 57% for Salmonella, in unenhanced and enhanced samples, respectively, relative to the pathogen control. D_55°C for Salmonella was the same or significantly less than for O157 and non-O157 STEC, regardless of heat shock, and was significantly less than for O157 and non-O157 STEC in all trials with moisture-enhanced meat (P < 0.05). Moisture-enhancing ingredients significantly increased D_55°C, regardless of pathogen (P < 0.05). We suggest that thermal processes validated against Salmonella may not prove effective against STEC in all cases and that regulators of the beef industry should focus attention on STEC in nonintact moisture-enhanced beef products.

Inactivation of Escherichia coli O157:H7 in Beef Roasts Cooked in Conventional or Convection Ovens or in a Slow Cooker under Selected Conditions

Inactivation of Escherichia coli O157:H7 in beef roasts cooked under selected cooking conditions was evaluated. Eye of round roasts were each inoculated at five sites in the central plane with a five-strain cocktail of E. coli O157:H7 at ca. 6.3 log CFU per site and cooked to center temperatures of 56 to 71°C in a convection oven set at 120, 140, 180, or 200°C, in a conventional oven set at 120 or 210°C, and in a slow cooker set on high or low. Prime rib roasts were each inoculated at 10 sites throughout the roast with the same E. coli O157:H7 cocktail at ca. 6.6 log CFU per site and cooked in the conventional oven set at 140 or 180°C to center temperatures of 58 to 71°C. The number of sites yielding E. coli O157:H7 after cooking decreased with increasing roast center temperature for the eye of round roasts cooked in the convection oven or in the slow cooker at a given setting, but this trend was not apparent for roasts of either type cooked in the conventional oven. Reductions of E. coli O157 in both types of roasts were generally less at the center than at other locations, particularly locations closer to the surface of the meat. When eye of round roasts were cooked to the same center temperature in the convection oven, the reduction of E. coli O157:H7 increased with increasing oven temperature up to 180°C and decreased after that. The reduction of E. coli O157:H7 in replicate roasts cooked under conditions in which the organism was not eliminated during cooking mostly differed by >1 log CFU per site. However, E. coli O157:H7 was not recovered from any of the inoculation sites when eye of round roasts were cooked to 65, 60, 60, or 63°C in the convection oven set at 120, 140, 180, and 200°C, respectively; cooked to 63 or 71°C in the conventional oven set at 120 and 210°C, respectively; or cooked to 63°C in the slow cooker set at high or low. For prime rib roasts, E. coli O157:H7 was not recovered from any of the inoculation sites in roasts cooked to 71 or 58°C in the conventional oven set at 140 and 180°C, respectively.