Food Protection Trends - November/December 2021 - 571

TABLE 1. Time and holding temperature combinations for sous-vide cooking
46°C
51°C
150 min
420 min
150 min
193.5 min
258 min
322.5 min
Precision Cooker, Anova Applied Electronics, Inc., San
Francisco, CA) for cooking. Duplicate steak samples were
taken from raw inoculated steaks (prior to cooking) and from
steaks at each hold time and temperature combination (Table
1). The median sampling times for 54 and 62°C were taken
directly from the USDA-FSIS Appendix A 5-log reduction
table, and the other times were ±25% of the median time.
The median sampling time for 51°C was extrapolated from
the thermal death curve used for the 5-log reduction table.
The 46°C sampling times represented potential worstcase
scenarios for sous-vide cooking at low temperatures
and were based on recommendations found in commonly
distributed sous-vide recipes. Steaks were submerged in the
sous-vide water bath and cooked according to the previously
stated times. For each temperature treatment, the internal
temperature was monitored in one steak that had been
fitted with a Type T thermocouple and TC-08 Data Logger
(Omega Engineering Inc., Norwalk, CT) and sealed into a
bag with an air-tight sealed septum. Come-up times for each
cooking treatment were approximately 80 min for 46°C,
70 min for 51°C, 50 min for 54°C, and 45 min for 62°C.
After samples were removed from the water bath, they were
immediately submerged in an ice-water bath and allowed to
cool for at least 15 min. After cooling, steaks were removed
from the individual vacuum pouches, and core samples
(25 g) were cut from each steak with flame-sterilized core
cutters and knives. Each core sample was then homogenized
in 100 g of buffered peptone water (Becton, Dickinson,
and Company, Franklin Lake, NJ) in a benchtop stomacher
(Stomacher 400, Seward, London, UK). Homogenates were
then serially diluted and plated onto EC Peal plates (Charm
Sciences, Lawrence, MA) according to the manufacturer's
instructions. E. coli colonies were enumerated after 24 h at
35°C according to the manufacturer's guidelines.
Statistical analysis
The experiment was conducted as three independent
replications with six total steaks for each sampling time and
temperature combination. Mean E. coli levels were reported
as log CFU per gram. Reductions were determined by
subtracting levels at given sampling times from the levels in
the raw sample. Data were analyzed using a general linearized
model with consecutive contrasts within temperature
treatments (α = 0.05) with the Statistical Analysis Software
(SAS 9.4, SAS Institute, Cary, NC). To maximize statistical
power, comparisons of E. coli levels between temperatures
were not analyzed.
RESULTS AND DISCUSSION
Temperatures of 51, 54, and 62°C all achieved 5-log
reductions of E. coli during sous-vide cooking of the nonintact
steaks, with reductions of 5.80, 6.62, and 6.83 log CFU/g
achieved at 258, 64.5, and 2.25 min, respectively (Table 2).
Reductions at the longest cook times for 51, 54, and 62°C
treatments were all >6 log CFU/g. In the samples cooked
at 46°C, E. coli levels after 150 min of holding were not
significantly different from the levels in the raw inoculated
samples, and even after 420 min of holding, only a 1.07-log
reduction was achieved.
The safety of potentially hazardous foods cooked via sous
vide has become a concern as the popularity of sous-vide
cooking has grown in both foodservice and domestic settings.
The finding of the present study revealed that the time and
temperature combinations recommended by some sous-vide
equipment manufacturers and popular chefs for nonintact
products may not be safe. Studies have been conducted on
other potential avenues of pathogen control. Juneja et al.
(11) evaluated the thermal death times of E. coli O157:H7
in sous-vide cooked ground beef with and without natural
antimicrobial extracts. Although the tea and apple extracts
blended into the ground beef samples acted as antimicrobials
and were able to decrease the temperature needed to inactivate
E. coli O157:H7 compared with the controls without extracts,
the lowest temperature tested was 55°C, which is much higher
than the temperatures suggested in many recipes. Thus,
the evaluation of nonintact meat sous-vide cooked to final
temperatures <54°C was investigated in the present study.
Beef steaks internally inoculated with the nonpathogenic
E. coli ATCC 25922 were cooked to final temperatures
below those recommended in the USDA-FSIS Appendix
A to address concerns about potentially unsafe sous-vide
cooking recommendations for nonintact meat. Hold time and
temperature combinations taken from the Appendix A 5-log
reduction table were sufficient to achieve >5-log reductions of
November/December Food Protection Trends 571
54°C
64.5 min
86 min
107.5 min
62°C
2.25 min
3 min
3.75 min
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