Food Protection Trends - May/June 2014 - 133

To conduct studies on the safety of acidified food, laboratory
conditions should be established that allow equal or greater
survival of the target vegetative microbial pathogens,
compared with survival under the conditions of the relevant
food products. For this reason, previous studies of thermal
processing or acid killing of vegetative pathogens in acidified
vegetables were done with cucumber juice medium (CJ,
to be described later) or cucumbers in a low-salt (2% or
less) brine as a medium representative of various acidified
vegetable products (1-4). Cucumbers do not contain
compounds that are known to be inhibitors of microbial
survival or growth, but cucumbers do contain amino acids,
sugars, and other compounds that may aid in the survival
of bacterial pathogens (1, 7). Many other vegetables or
ingredients typically present in acidified vegetable products,
including cabbage, peppers, garlic, horseradish and others,
contain antimicrobial compounds (8, 9). However, use of
media containing these natural antimicrobials for pathogen
reduction studies with acidified foods is problematic, because
the active concentration of these natural antimicrobials is

hard to quantify and may vary with cultivar, growing season,
weather, and other factors. Therefore, CJ was chosen to
represent a "worst-case" condition for the survival of bacterial
pathogens in thermal processing studies. Results of studies
that use CJ medium can be viewed as applicable to a variety
of acidified foods. Research with acetic acid and gluconic acid
(as a non-inhibitory buffer) in CJ medium (2-4) has been
used to support process filings for a variety of acidified food
products that may or may not contain cucumbers, including
flavorings, syrups, dressings, toppings, sauces, salsas, and
others
(F. Arritt and B. Ingham, personal communication).
The objective of this research was to define thermal
processing conditions that will ensure a 5-log reduction of
vegetative bacterial pathogens in acidified food products
that have pH values above 4.1 and below 4.6. Acetic acid
is perhaps the most common organic acid used in acidified
foods, particularly acidified vegetables. Acetic acid was
therefore included in CJ for thermal processing studies.
Gluconic acid, which has been shown to function as a non-

TABLE 1. Bacterial strains
Strain ID

Strain Name

Previous IDa

Food Origin

B0195

Listeria monocytogenes

SRCC 529

Pepperoni

B0196

Listeria monocytogenes

SRCC1791

Yogurt

B0197

Listeria monocytogenes

SRCC 1506

Ice cream

B0198

Listeria monocytogenes

SRCC 1838

Cabbage

B0199

Listeria monocytogenes

SRCC 2075

Diced coleslaw

B0200

Escherichia coli O157:H7

ATCC 43888

Laboratory strain

B0201

Escherichia coli O157:H7

SRCC 1675

Apple cider outbreak

B0202

Escherichia coli O157:H7

SRCC 1486

Salami outbreak

B0203

Escherichia coli O157:H7

SRCC 2061

Ground beef

B0204

Escherichia coli O157:H7

SRCC 1941

Pork

B0206

Salmonellab Braenderup

SRCC 1093

10% salted yolk

B0207

Salmonella Cerro

SRCC 400

Cheese powder

B0208

Salmonella Enteritidis

SRCC 1434

Ice cream

B0209

Salmonella Newport

SRCC 551

Broccoli with cheese

B0210

Salmonella Typhimurium

SRCC 1846

Liquid egg

SRCC strains obtained from Silliker, Inc., Chicago, IL; ATCC, American Type Culture Collection, Manassas, VA; ID,
identification

a

Salmonella enterica strains with the serotype (non-italicized)

b

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