Food Protection Trends - November/December 2021 - 570

raw or undercooked beef products. Cattle serve as a natural
reservoir for pathogenic E. coli, and beef surfaces may become
contaminated with these pathogens during slaughter and
fabrication (2, 4, 6, 8, 9). Although this contamination is a
surface concern in intact beef products, in nonintact beef
products such as an injection-marinated or blade-tenderized
steaks or roasts, pathogens can migrate from the surface of
the meat to the otherwise sterile interior during processing.
Thus, these products must reach an appropriate internal
temperature during cooking to ensure that they are safe to
consume. Meat processing establishments are required by the
U.S. Department of Agriculture, Food Safety and Inspection
Service (USDA-FSIS) to implement hazard analysis critical
control point (HACCP) plans with preventive measures to
produce meat products that are safe for human consumption
(15). The USDA-FSIS document " Guidelines for Meeting
Lethality Performance Standards for Certain Meat and
Poultry Products, " commonly known as Appendix A (16),
provides scientifically validated guidance for the control of
Salmonella, is a cornerstone for the production of cooked meat
products, and is commonly referenced in HACCP plans for
the prevention of pathogenic E. coli adulteration of cooked beef
products. Although this resource is widely used in industry,
home cooks are less likely to have this information.
Sous-vide cooking of meat commonly involves a final
high-heat finishing step such as searing or broiling to develop
color and flavor on the product surface (1), and this step is
typically sufficient for destroying pathogens on the surface
of intact meat products. However, this process may be
insufficient for the safe cooking of nonintact products in the
home because the final searing or broiling step may not result
in a sufficient or even appreciable increase in the internal
temperature of the product. Risk exists because some popular
chefs and manufacturers of sous-vide cooking equipment
may not adequately distinguish between intact and nonintact
products and may recommend cooking nonintact meat
products to final temperatures that are potentially not safe for
consumption. Some published sources recommend cooking
ground beef to internal temperatures as low as 46°C (7, 12).
One popular chef that works in partnership with a sousvide
equipment manufacturer recommends that consumers
purchase whole muscle cuts of beef and grind those cuts at
home to decrease the risk associated with sous-vide cooking
ground beef at low temperatures (12). A food safety risk
similar to this example could occur in a domestic setting
with products that are blade tenderized or marinated for an
extended period of time. Recommendations such as this may
lead to consumption of potentially unsafe beef products due to
the use of in-home cooking methods that are not adequately
validated for microbial safety. For cooking nonintact beef
products in the home, use of proper internal cooking
temperatures for a sufficient amount of time during the sousvide
step is the safest and most practical method for destroying
any vegetative pathogens that may exist in the product.
570 Food Protection Trends November/December
Limited research has been conducted on the quality of
sous-vide cooked meat products (3, 10). Our research group
evaluated the quality of beef steaks treated with combinations
of high-pressure processing and sous-vide cooking (13).
However, few projects have included evaluation of the safety
of individual sous-vide thermal processing procedures,
especially for cooking time and temperature combinations
below those recommended in Appendix A. Briggs et al. (5)
stated that lack of food safety guidance for sous-vide cooked
products in restaurants is a serious concern and that food
safety validation of individual recipes for safety is necessary.
A novel experiment utilizing low temperature sous-vide
cooking of nonintact beef was conducted to determine
whether holding time and temperature combinations
recommended by the USDA-FSIS in Appendix A could be
used for safe sous-vide cooking of nonintact beef products and
whether holding time and temperature parameters outside the
USDA-FSIS recommendations could potentially be used to
safely sous-vide cook beef products in a domestic setting.
MATERIALS AND METHODS
Inoculum preparation
Frozen stocks of E. coli ATCC 25922 biotype 1 (Manassas,
VA; a common laboratory quality control strain and
pathogen surrogate) were thawed, streaked for isolation
on tryptic soy agar, (Becton Dickinson, and Co., Franklin
Lake, NJ) and incubated statically for 24 h at 37°C to obtain
cultures in the late exponential phase of growth. For each
replication, a single colony was inoculated into 10 mL of
tryptic soy broth (TSB; Becton, Dickinson, and Company,
Franklin Lake, NJ) and incubated statically for 24 h at 37°C.
The 10-mL culture was added to 990 mL of fresh TSB and
incubated statically under the same conditions. On the day of
meat inoculation, two 1-L bottles of culture were combined
in a sterile metal tub to facilitate meat immersion.
Steak inoculation and sous-vide cooking
Beef semitendinosus muscles (IMPS 171C) were received
from a local meat packing facility. Steaks of 2.4 cm thickness
were cut perpendicular to the long axis of the entire muscle,
vacuum packaged, and stored frozen until use. For each
replication, steaks were thawed (48 h, 4°C) prior to use and
exposed to UV light for 15 min on each side to reduce any
latent surface contamination. To emulate the creation of the
contamination of a nonintact product (e.g., blade tenderized
steaks), steaks were internally inoculated with 2 L of E. coli
ATCC 25922 liquid inoculum (prepared as above) grown
to at least 8.5 log CFU/mL. Each steak was placed in the
inoculum and pressed with a pin pad inserted five times
into each side of each steak to ensure adequate migration
of bacteria to the interior of the steak. After inoculation,
steaks were air dried (30 min, 23°C), individually vacuumed
sealed (3 mil; Clarity, Koch Supplies, Riverside, MO), and
then transferred to preheated sous-vide water baths (Anova
Food Protection Trends - November/December 2021

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