Food Protection Trends - November/December 2017 - 412

from 150 min for E. coli O157:H7 heated at 52°C, with
30 min sampling intervals, to 6 min for S. enterica heated
at 58°C, with 1 min sampling intervals. Heating times in
acidified tomato purée at 54°C ranged from 60 min for E.
coli O157:H7 at pH 4.2 (citric acid), with 10 min sampling
intervals, to 4 min for S. enterica at pH 3.8 (acetic acid),
with 30 s sampling intervals. At least four independent trials
were conducted for each of the temperature/pH/acidulant/
pathogen combinations.
Whirl-Pak bags containing inoculated tomato purée
were kept fully submerged in a circulating water bath
(Thermo Scientific Phoenix II, Newington, NH) during
heating. The water level in the circulating water bath was
maintained at 1-2 cm above the level of the purée in the
Whirl-Pak bag at all times. Internal purée temperature was
measured using a digital data logger (HH506RA Multilogger thermometer, OMEGA Engineering, Inc., Norwalk,
CT) connected to sterile type "K-TC" thermocouple
probes placed in the top 2-3 cm of the purée and in the
geometric center of the purée. The water bath temperature was monitored using a calibrated mercury-in-glass
thermometer. Preliminary experiments indicated no
significant temperature differences (≤ 0.5°C) attributable
to location or time in tomato purée; the system was
isothermal and at steady state.

determined using the re-parameterized non-linear Weibull
model of Breidt et al. (5) according to Eq. (1):
log(N) = log(N0) - 5(t/t*)β,

(1)

where N is the cell count (CFU/ml) at time t, N0 is the
cell count at time zero, t* is the time when the log reduction
value (LRV = log(N0/N)) equals 5, and β is a curve shape
parameter (β = 1 is linear, β < 1 is concave up, β > 1 is
concave down). As described in (10), D* = t*/5, where D*
is the decimal reduction time.
For experiments with unacidified tomato purée (pH 4.5),
analysis of the temperature dependence of D* was according
to the z-value of Eq. (2):
log (D*T1/D*T2) = (T2-T1)/z,

(2)

Enumeration of surviving cells
At designated intervals, 1 ml samples of inoculated and
heated tomato purée were drawn and diluted into pre-chilled
(2-3°C) 9 ml BPD. Time-zero sampling occurred within
20 s of inoculation and mixing. Comparison of the cocktail
inoculum count to the time-zero count indicated an average
recovery of 102.6% (range 92.6-108.2%) for inoculum in
tomato purée (data not shown).
At each time point, samples were serially diluted in BPD
at 21°C and 0.1 ml aliquots were spread plated onto tryptic
soy agar (TSA; Difco) within 10 min of sampling. E. coli
O157:H7 and S. enterica culture plates were incubated at
37°C for 24 h, and L. monocytogenes culture plates at 37°C for
48 h, and surviving pathogens enumerated. A sample of each
453 g bag of blanched, frozen, and thawed tomato purée was
plated on TSA to estimate native microbiota. Neither native
microbiota nor comtaminants were ever counted, and they
were rarely encountered in inoculated samples.

where D*T is the D*-value at temperature T, and z is the
temperature increase required for a decimal reduction in the
D*-value.
The mean and standard error for each of the three parameters of the re-parameterized nonlinear Weibull model
(log(N0), t*, β) were determined by use of the regression
protocol of the R software package (R Foundation for Statistical Computing, Vienna, Austria) from all time points of
the thermal death curve. Significant differences of t* values
for all trials in unacidified tomato purée at pH 4.5 were
determined with use of Tukey's HSD test in the R statistical software. Statistical differences between curve shape
parameter β and 1 for assessment of linearity for each of
the 116 trials were calculated by use of a one-sample Wald
z-test. D54°C values from acidification trials were compared
in PROC MIXED (20) (SAS version 9.4, SAS Institute,
Cary, NC) using a 3*2*2 factorial design with all possible
interactions for three pathogen types (E. coli O157:H7, Salmonella, Listeria) * two acidulants (acetic and citric acids) *
two pH levels (4.2 and 3.8). Additionally, D54°C -values for
tomato purée at pH 4.5 (acid control) and at pH 4.2 and
3.8, acidified with citrate or acetate, were compared using
a 3*5 full factorial design for all five treatments for each
pathogen, with no treatment factorial structure. Differences
in D54°C -values for acidification trials were determined by
Fisher's LSD test in the SAS statistical software. A significance cut-off value of 0.05 was used for all analyses.

Mathematical modeling and statistical analysis
Log-linear plots of the bacterial count (CFU/ml) versus
time were made for all trials; 52 trials were conducted with
pathogen cocktails in unacidified tomato purée (pH 4.5)
at 52-58°C, and 64 trials were conducted with pathogen
cocktails in tomato purée acidified to pH 4.2 or 3.8 with
citric or acetic acid. A successful trial included at least six
sampling points and resulted in a reduction of at least threelog units in surviving cells. Five-log reduction times were

RESULTS
Pathogen D-values in tomato purée at 54°C ranged from
20.98 min for E. coli O157:H7 (pH 4.5, unacidified) to 0.63
min for S. enterica (pH 3.8, acidified with acetic acid) (Table
2). Pathogen thermal inactivation curves were often not
linear (Weibull shape parameter (β) significantly different
from 1, P < 0.05) As Dufort et al. reported (10), 16 of 52
(31%) pathogen inactivation trials in unacidified tomato
purée resulted in nonlinear inactivation curves; likewise,

412

Food Protection Trends November/December



Table of Contents for the Digital Edition of Food Protection Trends - November/December 2017

The Cleanliness of Resusable Water Bottles: How Contamination Levels are Affected by Bottle Usage and Cleaning Behaviors of Bottle Owners
Impact of Carcass Anatomical Location on the Microbiological Profile of Beef Trimmings
Thermal Processing Parameters to Ensure a 5-log Reduction of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in Acidified Tomato-based Foods
Experimental Evaluation of Performance of Sampling Techniques for Microbiological Quantification on Carcass Services
Effect-based Analytics for Toxicological Screening - Concepts for Future Developments
Beyond the Bio - John Luchansky
PDF Highlight - Food Chemical Hazards and Food Allergy PDG
IAFP 2017 In Review
Industry Products
Coming Events
Food Protection Trends - November/December 2017 - Cover1
Food Protection Trends - November/December 2017 - Cover2
Food Protection Trends - November/December 2017 - 385
Food Protection Trends - November/December 2017 - 386
Food Protection Trends - November/December 2017 - 387
Food Protection Trends - November/December 2017 - 388
Food Protection Trends - November/December 2017 - 389
Food Protection Trends - November/December 2017 - 390
Food Protection Trends - November/December 2017 - 391
Food Protection Trends - November/December 2017 - The Cleanliness of Resusable Water Bottles: How Contamination Levels are Affected by Bottle Usage and Cleaning Behaviors of Bottle Owners
Food Protection Trends - November/December 2017 - 393
Food Protection Trends - November/December 2017 - 394
Food Protection Trends - November/December 2017 - 395
Food Protection Trends - November/December 2017 - 396
Food Protection Trends - November/December 2017 - 397
Food Protection Trends - November/December 2017 - 398
Food Protection Trends - November/December 2017 - 399
Food Protection Trends - November/December 2017 - 400
Food Protection Trends - November/December 2017 - 401
Food Protection Trends - November/December 2017 - 402
Food Protection Trends - November/December 2017 - Impact of Carcass Anatomical Location on the Microbiological Profile of Beef Trimmings
Food Protection Trends - November/December 2017 - 404
Food Protection Trends - November/December 2017 - 405
Food Protection Trends - November/December 2017 - 406
Food Protection Trends - November/December 2017 - 407
Food Protection Trends - November/December 2017 - 408
Food Protection Trends - November/December 2017 - Thermal Processing Parameters to Ensure a 5-log Reduction of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in Acidified Tomato-based Foods
Food Protection Trends - November/December 2017 - 410
Food Protection Trends - November/December 2017 - 411
Food Protection Trends - November/December 2017 - 412
Food Protection Trends - November/December 2017 - 413
Food Protection Trends - November/December 2017 - 414
Food Protection Trends - November/December 2017 - 415
Food Protection Trends - November/December 2017 - 416
Food Protection Trends - November/December 2017 - 417
Food Protection Trends - November/December 2017 - 418
Food Protection Trends - November/December 2017 - Experimental Evaluation of Performance of Sampling Techniques for Microbiological Quantification on Carcass Services
Food Protection Trends - November/December 2017 - 420
Food Protection Trends - November/December 2017 - 421
Food Protection Trends - November/December 2017 - 422
Food Protection Trends - November/December 2017 - 423
Food Protection Trends - November/December 2017 - 424
Food Protection Trends - November/December 2017 - 425
Food Protection Trends - November/December 2017 - 426
Food Protection Trends - November/December 2017 - 427
Food Protection Trends - November/December 2017 - 428
Food Protection Trends - November/December 2017 - 429
Food Protection Trends - November/December 2017 - Effect-based Analytics for Toxicological Screening - Concepts for Future Developments
Food Protection Trends - November/December 2017 - 431
Food Protection Trends - November/December 2017 - 432
Food Protection Trends - November/December 2017 - 433
Food Protection Trends - November/December 2017 - 434
Food Protection Trends - November/December 2017 - 435
Food Protection Trends - November/December 2017 - 436
Food Protection Trends - November/December 2017 - 437
Food Protection Trends - November/December 2017 - Beyond the Bio - John Luchansky
Food Protection Trends - November/December 2017 - 439
Food Protection Trends - November/December 2017 - 440
Food Protection Trends - November/December 2017 - PDF Highlight - Food Chemical Hazards and Food Allergy PDG
Food Protection Trends - November/December 2017 - 442
Food Protection Trends - November/December 2017 - 443
Food Protection Trends - November/December 2017 - 444
Food Protection Trends - November/December 2017 - IAFP 2017 In Review
Food Protection Trends - November/December 2017 - 446
Food Protection Trends - November/December 2017 - 447
Food Protection Trends - November/December 2017 - 448
Food Protection Trends - November/December 2017 - 449
Food Protection Trends - November/December 2017 - 450
Food Protection Trends - November/December 2017 - 451
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Food Protection Trends - November/December 2017 - 453
Food Protection Trends - November/December 2017 - 454
Food Protection Trends - November/December 2017 - 455
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Food Protection Trends - November/December 2017 - 457
Food Protection Trends - November/December 2017 - 458
Food Protection Trends - November/December 2017 - 459
Food Protection Trends - November/December 2017 - 460
Food Protection Trends - November/December 2017 - 461
Food Protection Trends - November/December 2017 - 462
Food Protection Trends - November/December 2017 - 463
Food Protection Trends - November/December 2017 - 464
Food Protection Trends - November/December 2017 - 465
Food Protection Trends - November/December 2017 - 466
Food Protection Trends - November/December 2017 - 467
Food Protection Trends - November/December 2017 - 468
Food Protection Trends - November/December 2017 - 469
Food Protection Trends - November/December 2017 - 470
Food Protection Trends - November/December 2017 - 471
Food Protection Trends - November/December 2017 - 472
Food Protection Trends - November/December 2017 - 473
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Food Protection Trends - November/December 2017 - 475
Food Protection Trends - November/December 2017 - 476
Food Protection Trends - November/December 2017 - 477
Food Protection Trends - November/December 2017 - 478
Food Protection Trends - November/December 2017 - 479
Food Protection Trends - November/December 2017 - 480
Food Protection Trends - November/December 2017 - 481
Food Protection Trends - November/December 2017 - 482
Food Protection Trends - November/December 2017 - 483
Food Protection Trends - November/December 2017 - 484
Food Protection Trends - November/December 2017 - 485
Food Protection Trends - November/December 2017 - 486
Food Protection Trends - November/December 2017 - 487
Food Protection Trends - November/December 2017 - 488
Food Protection Trends - November/December 2017 - 489
Food Protection Trends - November/December 2017 - 490
Food Protection Trends - November/December 2017 - 491
Food Protection Trends - November/December 2017 - 492
Food Protection Trends - November/December 2017 - 493
Food Protection Trends - November/December 2017 - 494
Food Protection Trends - November/December 2017 - 495
Food Protection Trends - November/December 2017 - 496
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Food Protection Trends - November/December 2017 - 498
Food Protection Trends - November/December 2017 - 499
Food Protection Trends - November/December 2017 - 500
Food Protection Trends - November/December 2017 - 501
Food Protection Trends - November/December 2017 - 502
Food Protection Trends - November/December 2017 - 503
Food Protection Trends - November/December 2017 - 504
Food Protection Trends - November/December 2017 - 505
Food Protection Trends - November/December 2017 - 506
Food Protection Trends - November/December 2017 - 507
Food Protection Trends - November/December 2017 - 508
Food Protection Trends - November/December 2017 - 509
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Food Protection Trends - November/December 2017 - 513
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Food Protection Trends - November/December 2017 - 517
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Food Protection Trends - November/December 2017 - 519
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Food Protection Trends - November/December 2017 - 523
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Food Protection Trends - November/December 2017 - 529
Food Protection Trends - November/December 2017 - 530
Food Protection Trends - November/December 2017 - 531
Food Protection Trends - November/December 2017 - 532
Food Protection Trends - November/December 2017 - 533
Food Protection Trends - November/December 2017 - Industry Products
Food Protection Trends - November/December 2017 - 535
Food Protection Trends - November/December 2017 - 536
Food Protection Trends - November/December 2017 - 537
Food Protection Trends - November/December 2017 - 538
Food Protection Trends - November/December 2017 - 539
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Food Protection Trends - November/December 2017 - 541
Food Protection Trends - November/December 2017 - 542
Food Protection Trends - November/December 2017 - 543
Food Protection Trends - November/December 2017 - Coming Events
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