Food Safety
Controlling
Contamination
Focus on
Low-Moisture Food Products
By Brenda Stahl, Ph.D.
W
hen thinking of foodborne bacteria, mold and yeast outbreaks
that have plagued our industry
during the last 25 years, we generally reflect
on items that are considered high risk: lettuce, alfalfa sprouts, beef, deli meats and
soft cheeses. The explanation for these
items being high-risk lay directly in the
composition of the products – medium
to low in fat, high in protein, and most
importantly, high in available moisture.
Specifically these products have a high
water activity (Aw), which is defined by
the ratio of water vapor pressure of food to
the vapor water pressure of pure water at a
specific atmosphere. More directly, this is
the amount of available, free water within
a food product. While microorganisms
continue to change their preferences and
tolerances, there is a general rule that most
bacteria prefer an Aw of >0.90, whereas yeast
and molds will persist in Aw >0.70. Figure
1 shows the water activity ranges for some
foods, and the associated microbes that
prefer to grow in those associated ranges.
A food item is considered high moisture
if its Aw is >0.95, medium moisture with
Aw >0.85, and low moisture is generally
Aw <0.84.
The basic recommendation given to
most food manufacturers with respect to
low-moisture items was that most bacteriological issues should not be an issue, as
the water activity present in these foods
was refractory for microbiological growth.
Given recent wide-spread contamination
events, including peanut butter and peanut
butter paste (Aw 0.70), cookie dough (Aw
0.80), pistachios (Aw 0.72), milk chocolate
july/august 2010 AIB UPDATE 7
Food Safety
(Aw 0.65) and hydrolyzed vegetable protein
(Aw 0.60), the industry is now realigning
its recommendations to better combat the
potential for low-moisture food contamination. The concerns of these outbreaks are
led primarily by Salmonella species, as well
as E. coli, but are not limited in scope to
these two organisms.
Focusing on Salmonella in low-moisture
products, a number of outbreaks of Salmonellosis have been associated with the
consumption of ready-to-eat low-moisture
products, including chocolate, powdered
infant formula, raw almonds, toasted oats
breakfast cereal, dry seasonings, paprikaseasoned potato chips, dried coconut,
infant cereals and, more recently, peanut
butter and children’s snacks made of puffed
rice and corn with a vegetable seasoning.
More than 200 cases of Salmonellosis were
attributed to toasted oats cereal in 11 states
between April and June 1998, more than
600 cases were attributed to peanut butter/
peanut butter paste in 47 states between
August 2006 and May 2007, and more
than 500 cases have been attributed to peanut butter and peanut butter-containing
products in 43 states between September
2008 and January 2009. Due to the large
number of unreported cases of Salmonellosis for all types of products, the actual
number of cases was likely much higher.
How can Salmonella and similar bacterial contamination be prevented in your
low-moisture facility? We have uncovered
four essential steps that, when employed,
will help alleviate this potent bacteriological
stressor in your products and food processing environments.
STEP 1: KEEP IT DRY!
The rules for cleaning and environmental
control in a dry- or low-moisture plant
environment are quite simple: if the environment is dry, keep it dry. It is necessary
to periodically use water in some dry
environments to clean certain equipment.
This process removes accumulated product
residue that can lead to process inefficiencies or dangerous build-ups, as well as
leaving residue that becomes noticeable in
the product. Due to the requirement for
water usage, special considerations should
be made including the review of current
8 july/august 2010 AIB UPDATE
practices to help minimize water usage
in dry areas, traffic flow analyses to help
minimize migration of people and plant
equipment (such as forklifts) from wet to
dry areas, and employee compliance with
Good Manufacturing Practices (GMPs).
Enforce divisional rules from wet-to-dry
areas, and be sure to have procedures in
place if any moisture is either introduced
into or forms in a dry area at any time.
Maintaining a dry environment will
lessen the ability for microbes to colonize
within the facility, on items such as cracks,
sponges, condensation gathering areas,
drains, or poorly maintained air filters and
fans. In review of your current practices,
ensure such items as discontinuing the use
of water hoses to clean during production,
using a sanitizer when draining to a floor
drain, and proper storage off of the floor
of hoses and other materials.
Evaluation of your equipment and
material flow throughout the facility
is important to maintaining a dry
environment. Having dedicated equipment
for wet/dry areas, as well as designating
specific personnel and personnel clothing
and equipment for each of the areas will
help in keeping items from transferring
between the wet and dry environments
in your facility. For those workers who
do travel between areas, the addition of
footwear baths and drying areas outside of
each area will help prevent potential carry-
over into the new environment.
Lastly, improving GMP knowledge and
training on dedicating wet and dry areas is
the first line of defense in controlling unwanted bacterial traffic. Ensure employees
understand items such as dry footwear, raw
material handling and proper storage, and
movement of materials between dedicated
areas of the facility.
STEP 2: BE A MICROBIAL NICHE DETECTIVE!
There are two categories of microorganisms
that are present in a food process – those
that are transiently introduced, and those
that are resident within the products.
Transient microorganisms can be introduced into food environment routes such
as air flow, raw materials, uncontrolled
pest contamination and a breakdown in
GMPs. Routine application of GMPs and
sanitation procedures is essential to remove
or kill transient microflora during cleaning
and disinfection. In some cases, however,
certain transients can become established,
multiply and persist over time.
Persistent microflora can exist in biofilms or in niches in the food processing
environment for decades. Biofilms occur
when microorganisms become attached
or immobilized on a surface, often within
a matrix of microbially produced organic
polymers, and provide favorable conditions
for growth and survival (e.g., increased
resistance to disinfectants). Biofilms are
Figure 1. The Relationship Between Microbes, Aw and Food
MICROBES
WATER
ACTIVITY
FOOD
E. coli
Campylobacter
Clostridium
Listeria
Aw = 1.0
Most Bacteria
Staphylococcus
Aw = 0.9
Molds, Yeasts
Aw = 0.8
Jams, Pepperoni, Honey, Condensed Milk
Salmonella
Aw = 0.7
Peanut Butter and Paste, Rolled Oats, Dried
Fruits, Caramel, Crackers
Aw = 0.6
Dehydrated Foods
Fresh Vegetables, Fruits, Meats, Fish, Milk
Cured Meats, Soft Cheeses
Dry Cheeses, Sugar, Syrups
Flour, Cakes, Rice, Beans, Cereals
Food Safety
third-party laboratory, or in-house AOAC
approved method for determining the presence/absence of potential microbiological
hazards, and most importantly – tabulate
your historical analytical data to observe
changes in areas over time. Be sure to
evaluate new and different areas in your
facility on an intermittent basis to ensure
these areas are not harboring any unwanted,
persistent bacteria.
By being your facility’s own “bacterial
niche sleuth”, you will constantly be in control of the potential for transient contamination, and will be proactively intervening
to ensure the safety of your products.
The rules for cleaining and environmental control in a dry- or low-moisture plant environment are
quite simple: if the environment is dry, keep it dry.
common in closed systems such as in pipes
and heat exchangers and on gaskets that
are infrequently or inadequately cleaned.
The persistence of Salmonella and Listeria
monocytogenes in floor drains is largely due
to the potential for biofilm formation of
these two bacterial species. Niches occur in
sites where food and moisture accumulate
(e.g., inside the hollow supports and legs
of equipment, inside hollow rollers for
conveyors, in oil and grease reservoirs with
worn seals, between close-fitting materials
such as metal-to-metal or metal-to-plastic
units). Niches are also sites that are not
normally cleaned and disinfected.
Biofilms and niches are of greatest
concern when located after a kill step (e.g.,
cooking) in a process. In both cases the
environment appears visually clean and
will pass inspection. Traditional sampling
for indicators before start of operation to
verify the equipment is clean will not detect
the presence of a biofilm or niche. During
production, movement or vibrations of the
equipment and/or flow of food through
the system causes some of the microorganisms in biofilms and niches to become
dislodged and contaminate the food. It is
only through microbiological sampling of
the equipment or food during production
that biofilms and niches are revealed and
corrective actions can be taken.
Factors (e.g., temperature, Aw, pH, nutrient content) that influence the ability of
microorganisms to multiply in laboratory
media also influence the number and type
of microorganisms that occur in biofilms
and niches in food processing environments. Dry processes, including blending,
spice manufacturing and flour milling are
generally more controllable due to the
lack of free moisture. More controllable
does not mean free from contamination
potential. Leaking roofs, pipes and hose
stations and condensation that form when
warm moist air contacts cold surfaces are
additional sources of moisture that can occur, and these areas should be an integral
part of the environmental sampling regime
for the facility.
Prevention of niche and biofilm formation should start with your equipment.
Redesigning or replacing equipment using
materials that are durable, have smooth surfaces and are easily cleanable, paired with a
validated Preventive Maintenance Program,
will help prevent contamination in areas
that are cracked and in need of repair.
The most effective strategy for detecting and controlling the influx of transient
microorganisms in your facility is a robust
environmental sampling program. Coordinate a facility-wide, site-specific program that periodically evaluates food and
non-food contact surfaces, air-handling
systems, and manufactured products themselves over a specific time interval (week,
bi-monthly, month). Use an accredited
STEP 3: Clean, sanitize, VALIDATE!
Proper sanitation procedures are the primary line of defense against transient and
problematic microbial contaminations.
Ensuring sufficient training on the use of
sanitizers, how to effectively clean certain
food-contact areas and hard-to-reach surfaces, as well as training on the materials
themselves are paramount in maintaining
a truly clean work environment. Several
monitoring steps should be employed in
each system, including:
• Visually and physically inspect food
contact surfaces of equipment and utensils to ensure the surfaces are clean.
• Visually and analytically monitor the water used to verify a clean, potable source.
• Verify thermometer accuracy by using
a calibrated thermometer when water
temperature is specified.
• Validate the sanitizer concentration by
using the appropriate test kit for the
chemical.
Following direct sanitation procedures
and validating the procedure on a regular
basis should be fundamental to the training process for sanitation employees, as
well as shift personnel in the event of an
in-process line-contamination cleaning
issue. Additionally, the effectiveness of
sanitizers used for specific areas (stainless
steel food-packaging line vs. floor drain in
maintenance workshop) should be evaluated on a periodic basis.
A major need for validation of sanitizer
efficacy is due to the changing tolerances
to bacteria in low-moisture environments.
With respect to Salmonella-related outjuly/august 2010 AIB UPDATE 9
Food Safety
breaks in low-moisture food items, it is
necessary to set critical limits for the organism in your environment, as well as identify
that these critical limits are being met and
maintained by your sanitizer of choice. The
efficacy of sanitizers decreases significantly
over the period of their use, and should
be evaluated to ensure that the perceived
intervention in the facility is accurately being met. A simple efficacy test for sanitizers
includes swabbing an area prior to sanitization, directly post-manufacturing. Swab the
area again 2-3 hours after sanitizing, as well
as every 2-3 hours until the following day’s
post-manufacturing period. Evaluate the
sanitizer’s ability to maintain a bacterially
controlled environment. In most cases, a
sanitizer will remain effective for a period of
6-12 months when used as the sole sanitizer
in a given process. For optimum efficacy
and longevity, use 2-3 different sanitizers
for a “hurdle” effect, where the sanitizers
will compete together against unwanted
contamination and rotate different sanitizers in areas of the facility.
STEP 4: BE A RAW MATERIAL HISTORIAN!
No matter what link you may be in the food
supply chain, ensuring that your suppliers
are delivering safe, wholesome raw materials, ingredients or finished products is the
first step in process control. “Bacterially
sensitive” ingredients are ingredients that
have been historically associated with a
bacterial species (tested positive for the
pathogen), have been implicated in past
outbreaks, or are used to make products
that are intended for at-risk individuals.
Even in the manufacture of low-moisture
products, critical evaluation of raw materials is essential in controlling your food
safety program.
One simple way to achieve peace-ofmind about your incoming ingredients
is to invest in a Vendor Quality Program
(VQP). A VQP enables your operation to
systematically track performance of your
vendors and verify compliance to your
quality and food safety specifications to
see which provide the most benefit, from
both a food safety and a business perspective. Such programs include evaluation of
the supplier’s food safety program with
respect to pathogen environmental moni10 july/august 2010 AIB UPDATE
In recent recalls a number of outbreaks of Salmonellosis have been associated with the consumption of
ready-to-eat low-moisture products such as cereals and raw nuts.
toring, sanitation practices, raw materials/
ingredients storage, finished product hold
and release testing, process validation, and
a corrective action plan if positive microbiological results are found.
The first step in developing a VQP
is to make certain you have a thorough
understanding of your own processes and
products and then understanding how your
products move through the supply chain,
upstream and down. This working knowledge will help you identify the key points
of product receipt and transfer within your
own, your vendors’ and your customers’
systems in order to best target those points
where your operation’s performance tracking measures will yield the most value in
terms of food safety and efficiencies. More
critically, you will be able to identify ingredients or areas of concern from suppliers
and be prepared to set agreeable targets and
limits for product specification.
In preparation for your raw materials,
maintain a historical reference to their
production processes, possible contamination and/or quality issues. Do not rely
on Certificates of Analysis (CoA) to give
you all of the background information on
the product, and judge the criteria within
the CoA to determine if the supplier has
tested for all items that could be a concern
with respect to the product and your intentional use.
In March, 2010, the FDA responded to
a Salmonella outbreak concerning Hydrolyzed Vegetable Protein (HVP), a common
ingredient used most frequently as a flavor
enhancer in many processed foods, includ-
ing soups, sauces, chilis, stews, hot dogs,
gravies, seasoned snack foods, dips and
dressings, produced by one manufacturer
with a broad supplier base. This product
is a powdered, low-moisture ingredient
with presumably little concern in terms of
microbiological contamination. Due to the
contamination found at the manufacturing
site, the company is recalling all hydrolyzed
vegetable protein in powder and paste form
that it has produced since Sept. 17, 2009.
Subsequently, all uses of this product (177
types of products as of 4/1/2010) have also
subsequently been recalled and withdrawn
from the market. With a strong, reliable
VQP, in which the manufacturer’s processes
were strongly evaluated, one would wonder
if the manufacturers of those 177 different
products could have avoided what is likely
a major economic loss. When items that
have no previous relationship to foodborne
outbreaks become the vehicles of contamination in low-moisture products, a vigorous
VQP can serve as your product’s security
against such instances.
In comparison to high-risk products,
low-moisture products have traditionally been left out of bacteria-specific zerotolerance programs, such as qualified for
Listeria and E. coli in the red meat industry.
With the advances in bacterial persistence
in low-moisture foods, we need to work
cooperatively to prevent these products from
continuing to catapult bacterial corruption
and foodborne outbreaks in the future. AIB
The author is Director of Microbiology, AIB International.