Food Protection Trends - November/December 2017 - 410

the food under the conditions in which the food is stored,
distributed, retailed and held by the user (22). For acidified
foods, thermal processing is normally a mild heat treatment,
such as steam pasteurization or an inverted hot-fill hold that,
for low pH products, is generally sufficient to guarantee
safety (2).
In the manufacture of acidified canned foods, acidification
is most often accomplished by addition of organic acids such
as acetic, lactic or citric acid, singly or in combination, and
employed to control microbial growth, improve sensory
attributes, and reduce microbial spoilage of foods (1, 9, 15).
In a review of 179 tomato-based acidified food products
found in local grocery stores, we noted that citric and acetic
acids were the most commonly used acidulants, usually in the
form of lime juice or distilled vinegar. Citric acid has been
shown to inactivate Salmonella Typhimurium in tahini (1),
while acetic acid has been shown to inactivate Escherichia coli
O157:H7 in simulated pickle products (4) and apple-carrot
juice blends (23). Acetic acid was also effective at inactivating
Salmonella, E. coli O157:H7, and L. monocytogenes to various
degrees in asparagus purée (20). Acetic and citric acids have
been shown to inactivate E. coli O157:H7, Salmonella, and
L. monocytogenes on fresh apples and lettuce (18) and in
cucumber purée (3).
Processors of acidified canned foods are required to register their manufacturing facility and file scheduled processes
for their products with the Food and Drug Administration
(FDA) (22). FDA filings for acidified canned foods must be
supported by research that validates destruction of important foodborne pathogens, and E. coli O157:H7, S. enterica,
and L. monocytogenes are considered targets for thermal processing and acidification (5-7). The work of Breidt and colleagues used a re-parameterized Weibull model to estimate
thermal processing conditions necessary to achieve a 5-log
reduction of target pathogens in an acidified cucumber
juice medium (5-7). Recent studies in our laboratory have
confirmed the appropriateness of the non-linear Weibull
approach for calculating accurate thermal processing D- and
z-values (10).
The process authority, in using laboratory data to establish
a scheduled process for an acidified food, must rely on an
understanding of heat penetration in a particular food matrix,
the impact of formulation on microbial inactivation, and
heat tolerance of spoilage organisms and target pathogens.
It is in the best interest of manufacturers to have appropriate evidence to validate thermal processing conditions that
produce a safe but not over-processed product, leading to a
balance between food safety and food quality. In the absence of current recommendations developed with use of a
tomato-based medium, this study was conducted to calculate
thermal processing parameters that would inactivate vegetative cells of the target pathogens E. coli O157:H7, S. enterica
and L. monocytogenes in tomato purée. This study expanded
on previous work (10) and examined the effect of acidifica-

410

Food Protection Trends November/December

tion with citric and acetic acids on thermal inactivation of
these vegetative pathogens in tomato purée at 54°C. Time/
temperature processing conditions were estimated that would
ensure a minimum 5-log pathogen reduction of vegetative
pathogens and could be used to support safe manufacture of
tomato-based acidified canned foods.
MATERIALS AND METHODS
Strain selection and maintenance
Strains of E. coli O157:H7, S. enterica, and L. monocytogenes
were used in this study (Table 1). With one exception, these
strains were the ones used in work by Breidt et al. (5-7);
E. coli O157:H7 strain ATCC 43895 (American Type
Culture Collection, Manassas, VA) replaced strain ATCC
43888 used in the prior work. Stock cultures of each strain
were maintained in Tryptic Soy Broth at pH 7.1 (TSB;
Difco, Becton, Dickinson and Company, Sparks, MD)
containing 10% (v/v) glycerol (Fisher Scientific, Itasca,
IL) and stored frozen at -20°C. Bacterial strain identity
and purity were assessed and confirmed by Gram reaction,
cell and colony morphology, and responses to biochemical
profiling kits (bioMerieux, Durham, NC) for E. coli
O157:H7 and S. enterica (API 20E), and L. monocytogenes
(API Listeria). Working cultures were prepared monthly
by streaking for isolation from partially thawed stock
cultures onto appropriate selective plating medium: L.
monocytogenes on Listeria Selective agar (LSA; Oxoid LTD,
Basingstoke, Hampshire, England) with added Listeria
Selective Supplement (Oxoid), and S. enterica and E. coli
O157:H7 on modified Levine's Eosin Methylene Blue agar
(mLEMB; Difco). mLEMB was prepared from Levine's
Eosin Methylene Blue agar, with addition of D-sorbitol
(10 g/liter; Fisher) and NaCl (5 g/liter, Fisher). Working
culture plates were incubated at 35°C for 24 h for S. enterica
and E. coli O157:H7, or 48 h for L. monocytogenes, followed
by storage at 4°C for ≤ 40 days. E. coli O157:H7 colonies
appear colorless to pale pink on mLEMB agar, S. enterica
colonies appear dark red to iridescent green on mLEMB agar,
and L. monocytogenes colonies appear pale yellow or grey
surrounded by a black halo on LSA.
Inoculum preparation
For each trial, a 5-strain single-pathogen cocktail was
prepared. Inocula were prepared by the selection, for each
strain, of a single colony from a working culture plate, the
cells of which were suspended into 9 ml of TSB +1% added
glucose (Fisher) and statically incubated at 35°C for 24 ± 2
h to obtain stationary-phase cells (108-109 CFU/ml) and
expose growing cells to acid, as previously described (5, 8).
Contents of all five tubes for a species were combined in one
conical 50 ml centrifuge tube and harvested by centrifugation
(4,500 g, 7 min, 21°C, Marathon 21K, Fisher). The supernatant was discarded and the pellet was re-suspended in 4.5
ml Butterfield's Phosphate Diluent (BPD; Nelson Jameson,



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
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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
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Food Protection Trends - November/December 2017 - 467
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Food Protection Trends - November/December 2017 - 483
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Food Protection Trends - November/December 2017 - 485
Food Protection Trends - November/December 2017 - 486
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Food Protection Trends - November/December 2017 - 488
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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
Food Protection Trends - November/December 2017 - 540
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
Food Protection Trends - November/December 2017 - Cover3
Food Protection Trends - November/December 2017 - Cover4
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