Microbiological
Quality and Safety of FoodRevised 2003
Dr. Bohdan Slabyj, Dr. Alfred Bushway, Dr. Russell Hazen
Department of Food Science and Human Nutrition
University of Maine
Orono, ME 04473
Table of
Contents
INTRODUCTION
With the consumer’s increased awareness of food safety as well as
to assure a safe food supply, government agencies have been
implementing more rigorous inspections for nearly a decade.
At the same time, food processors have been searching for
uniform processing procedures to assure safe food.
These three factors lead the industry and government
agencies to develop the so-called HACCP (Hazard Analysis Critical
Control Point) program. While the HACCP program takes into account
three types of food hazards (biological, chemical and physical),
this publication will address only one aspect of the biological
hazards, namely the bacteriological quality and safety of food.
The microbiological quality and safety of food
will be discussed in general terms, although scientific terms will
be frequently introduced. The objective being
to give small food processors a better appreciation of the
significance that microorganisms play in food processing as well
as food safety. Thus, while individuals with minimal training in
microbiology may better understand the “science” behind the
various rules regarding food processing, individuals with some
formal training in microbiology, my find this publication a useful
review.
FOOD SPOILAGE AND
REFRIGERATION
Bacteria are tiny organisms that
cannot be seen with the naked eye, but their activity can readily
be observed. It does not take much effort to guess what would
happen if raw chicken, ground beef, or a fish fillet were left for
a weekend on the kitchen countertop during the summer.
Similar changes occur when the food
is refrigerated, but it takes considerably longer for the spoilage
to occur. Ideally, refrigerators should be running at 32°F, but
many of them, especially during the summer, run closer to 45 or
even 50°F.
Although spoilage to an average person would appear similar
at 32 and 90°F,
microbiologically it is not. In the microbial
world, there are thousands of different bacteria that compete with
each other. Therefore, those bacteria that grow faster than others
at a given temperature in a particular food, will predominate and
will be responsible for spoilage.
In most cases spoilage is due to a mixed flora, where
several different species contribute to spoilage.
Refrigeration slows the metabolism of bacteria and
therefore the rate of multiplication; consequently, we can delay
spoilage. However, we must be aware that a
lower temperature does not slow the different species of bacteria
to the same degree. Furthermore, many bacteria will not grow at
temperatures below 50°F.
Since temperature plays an important role in
bacterial multiplication, bacteria are divided into four classes
based on their growth temperature. There is a
very large group of bacteria, including many of the human
pathogens, that grow between 50 and 115°F
(mesophiles), while others will grow between 30 and 50°F
(psychrophiles). A third group can grow over a
large temperature range, between 32 and 115°F
(psychrotrophs). The last group of bacteria
grows at temperatures above 131°F
(thermophiles).
In the world of microorganisms one
finds bacteria, yeast, and molds as well as rickettsia and
viruses. Only bacteria, yeasts, and molds
(fungi) can grow in food (certain food). The bacterial cell has a
wall that determines the shape of that cell and is also
characteristic of that species.
There are three basic shapes: the cell can be spherical (coccus/cocci),
a straight rod (bacillus/bacilli), or a curved rod (vibrio/vibrios).
Many bacterial cells do not move (non-motile), while others
can swim about (motile). The ability to swim
depends on the presence of a whip-like structure(s)
(flagellum/flagella). There may be one
flagellum at one end of the cell (polar flagellum) or at both ends
(bipolar). Cells may have a tuft of flagella (lophotrichous)
and one or both ends of the cell. Other
bacteria have flagella all around the cell (peritrichous).
These characteristics are typical of a given species and
are frequently used to identify the culture.
Relatively few bacteria produce spores. The
spore is a resting stage of a cell and is significantly more
resistant to heat, detergents, sanitizers, UV light, dehydration,
ionizing radiation, chemicals, and other deleterious factors than
the corresponding vegetative cell. Some
bacteria also produce a capsule. This viscous layer that surrounds
the cell is responsible for the slime that is at times associated
with bacterial spoilage, and also offers the cell protection from
detergents and sanitizers.
One should not forget that bacteria also have “appendages”
(fimbriae and pilli), by which they may attach themselves to
surfaces. Bacterial cells can also adhere to
surfaces due to electrostatic charges. Capsules have been
observed to make bacteria stick to each other as well as to
surfaces on which they grow.
Bacteria multiply by simply dividing in two
(binary fission). Depending on characteristics of the species as
well as cultural conditions, these cells may stick together after
division or they may separate.
Furthermore, depending on the plane of cell division one
can observe different cell arrangements: single cells, pairs,
short chains, long chains, irregular arrangements, group of four
(tetrad) and various sized packets. These peculiarities are also
characteristic of different species and are used for
identification.
cell division
streptococci
single cells
diplococci tetrads
packets
staphylococci
Bacterial cells cannot be seen
under the microscope unless they are stained.
One method of staining is the Gram Stain. To accomplish this, a
smear is made on a glass slide and air died.
The cells are fixed to the slide by heating so that they
are not washed away during the staining process.
The slide is then flooded with Crystal Violet dye, followed
by Gram’s iodine solution. At this point an
attempt is made to decolorize the cells with alcohol, followed by
counter staining with Safranin (a pink stain).
Cells that are not decolorized will be purple when viewed under
the microscope and are called “Gram positive”. Decolorized
cells will be pink because they will have lost the purple stain,
but will have retained the pink counter stain.
Such cells are called “Gram negative”.
Gram reaction is important to remember because Gram negative cells
tend to be more susceptible to heat and disinfectants as compared
to Gram positive.
Furthermore, Gram-positive rods tend to have spores while
Gram negative bacteria do not. The Gram reaction is a reproducible
characteristic of a species and therefore is an additional tool
for bacterial identification.
Spoilage is the result of bacterial growth and the accumulation of
metabolic end products.
Odors produced will depend on the food item involved and
the predominant bacteria growing. It is
logical to assume that the bacteria present on a given food will
greatly depend on the bacteria that were present on the food
before harvest. Thus, bacteria most likely
found on meat will be different from those present on vegetables,
or those present on a fish fillet. Processed foods will carry
survivors of the process (as well as bacteria added by the
processing), bacteria introduced by post process contamination and
subsequent growth during storage.
This applies to meat and poultry products as well as
vegetables and seafood products (both raw and cooked).
In general, spoiled seafood is more odoriferous than meats,
while spoiled vegetables are least smelly, but not always.
If one were to determine the total number of bacteria present on a
food product at any given time, it may be difficult to decide what
that number indicates, unless an individual has knowledge of the
history of that product.
Bacterial load on a food item represents contamination
(transfer of bacteria from some source to the product) and
bacterial growth (spoilage). In order to determine the bacterial
load on a product, it is essential that the sample be collected
aseptically (without contamination).
This means that the sample must be collected with sterile
instruments and placed in a sterile container. Removing a
sample from a sealed package is best done in a laboratory, where
precautions can be taken to prevent contamination with bacteria
present on the surface of the package.
A sample collected for
microbiological analysis (a perishable product) must be
refrigerated (32-40°F)
and analyzed within 24 hours. If the product
is solid, such as fish or crabmeat, it is suspended in a sterile
buffer and homogenized or otherwise dispersed.
Not knowing how many bacteria may be present, serial decimal
dilutions are prepared and one-milliliter (ml) volumes are placed
in sterile Petri dishes. An appropriate agar medium that has been
previously sterilized by heating to 212°F for 15 minutes and
tempered to 113F° is then poured into the plate and swirled to mix
sample and agar.
This agar will cool quickly and at the same time it will
solidify, preventing individual bacterial cells from moving about.
Petri dishes are then inverted and
incubated at predetermined temperatures. For
quality control purposes, the plates are incubated at “room
temperature” (72 ± 4°F)
until visible colonies appear (two to five days, depending on the
product and the condition of bacteria). The
results are reported as Total Viable Count (TVC), or Colony
Forming Units (CFU) per gram of product.
Government regulations may require the plates to be incubated at
95°F, which then provides
the Aerobic Plate Count (APC). TVC, which is
obtained at room temperature, will be higher than the APC most of
the time, especially on refrigerated food. Neither approach
is flawless, but counts are comparable among laboratories using
identical procedures and therefore valuable.
Most spoilage bacteria require air
and are called the “aerobes”. Bacteria that
grow only in the absence of air, such as Clostridium botulinum,
are called the “anaerobes”. The third group of bacteria can grow
in the presence or absence of air and are called “facultative” and
includes many of the human pathogens.
Because the traditional procedure
to obtain TVC is time and labor intensive (media and glassware
preparation and sterilization), many attempts have been made to
simplify the procedures. Such procedures
include Little Plates, Roll Tubes, Spiral Counter, Hydrophobic
Grid Membrane, Petrifilm, Redigel, and others.
Spiral Counter, Hydrophobic Grid Membrane, and Membrane Filter
work better with liquid foods. Petrifilm and
Redigel have been simplified to the point that the analysis can be
performed in someone’s office. Catalase Meter
is another very simple procedure, based on the fact that many
bacteria possess the enzyme catalase.
Additional procedures include Direct Microscopic Count, Coulter
Counter, Flow Cytometer, Bactomatic, Bactometer, Malthus,
Bioluminometer, Electronic Strobe and others.
As indicated earlier, the type of spoilage that a particular food
will undergo depends on the predominant microorganism present on
that food, peculiarity of the food item in question and the
temperature of storage.
There is not enough space to discuss all aspects of
spoilage, but we must examine closer the effect that temperature
and the level of bacterial contamination exert on the spoilage
rate.
The higher the temperature of the
perishable product the faster it spoils. By
examining the growth curve more closely, it is possible to better
appreciate what is happening. Two factors are
controlled by temperature, the lag phase and the growth rate (rate
of cell division or generation time). As seen
in Figure 1, when the storage temperature of a perishable product
is reduced, the growth rate is reduced and the lag phase is
extended. Off odors (incipient spoilage) are
usually detected when bacterial numbers reach 106 to 107
CFU/G of the product.
Figure 1. Spoilage by a psychrotoroph at different
temperatures.
A given change in temperature at
the refrigeration range has a larger effect on shortening the
shelf life of the product than similar change at higher
temperature. Thus a 9° increase from 32 to 41°F will shorten the
shelf life by 149 hours, while the same 9° increase from 41 to
50°F will shorten the shelf life by 61 hours (see Figure 1).
The growth rate of a specific
psychrotoroph in a given product at the same temperature is the
same, despite the contamination level (Figure 2).
However, we should note that the lag phase is reduced as
the contamination level increases. From the
example given it is apparent that the lag period was reduced from
120 hours at 103 CFU/G initial contamination, to 41
hours at 106 CFU/G contamination or a 79 hour
difference. It may be more important to note
that spoilage at 107 CFU/G with 106 CFU/G
contamination was reached in 51 hours, while with 103
CFU/G contamination, spoilage was reached in 159 hours or a 108
hour difference. It is therefore of economic importance for food
processors to keep bacterial load on refrigerated products as low
as possible to secure a long shelf life.
Figure 2. Spoilage at 32°F
by a psychrotroph with different initial contamination.
Gram-negative bacteria, such as
Pseudomonas, tend to produce more foul odors than
Gram-positive bacteria, such a Bacillus or Streptococcus
species. Consequently, while incipient
spoilage by Gram-negative bacteria may be noticed at 106/G,
while Gram positive at 107/G may not be accompanied by
strong off odors. Vacuum packaging can extend
the shelf life of some products. This procedure inhibits the
Gram-negative bacteria that require oxygen for growth; thus the
production of foul odors is delayed.
The growth of Gram-positive bacteria, that are also present
in the vacuum-packaged product, is a little slower and their
metabolic products are not as objectionable.
Thus vacuum packaging does not stop spoilage, it only alters the
spoilage rate and the
nature of spoilage flora. Vacuum
packaging, however, carries with it a serious potential hazard
because if the product is temperature abused, Clostridium
botulinum will be able to grow. This point will be discussed
later in greater detail.
Red meats have a relatively long shelf life, whereas most fish
spoil noticeably faster.
This difference in spoilage rates is because fish is
usually wet (due to normal handling and processing procedures), it
is more digestible, a higher post rigor pH, it has less connective
tissue, and it has more soluble nutrients. All this adds to the
rapid bacterial spoilage of fish as compared to beef.
Another very important factor to
remember in spoilage is the size of the food particles: The
smaller the particle is, the larger the ratio of surface area to
weight. Foods with a large surface area to weight ratio are
subject to rapid bacterial spoilage.
Halibut or a side of beef when
properly handled may have a shelf life at 32°F
of more than two weeks. Large salmon, cod or
haddock will keep less than two weeks. Chicken will keep up to one
week at 32°F.
In these instances it is important to remove the viscera,
which will release digestive enzymes during storage and shorten
the shelf life. Small fish cannot be
economically eviscerated and thus spoil fast. Herring will
spoil at 32°F within a few days as will ground meat, where
bacterial cells are thoroughly dispersed throughout the product.
When an animal or fish dies
suddenly, glycogen (a high energy compound) will be present at
high level. Although respiration stops at
death, other enzymes are still functioning. Some of these
enzymes will break down glycogen to lactic acid.
In well-rested animals or fish, a pH of 7. 0 at death can
drop to as low as pH or 5. 6 or even lower.
This drop in pH is desirable because it inhibits growth of
spoilage bacteria. Unfortunately due to subsequent changes, the pH
will slowly rise to the neutral range.
Mollusks, such as clams, mussels
and oysters, are live if left in the shell. Their shelf life
depends on how long they can be kept alive.
If kept in humid, refrigerated storage, they will stay
closed and remain alive for some time. When dead, the shells will
gape, meaning they are not edible and must be discarded.
Fruits and vegetables are also
living entities when harvested. They have a
skin that prevents bacterial invasion, but they can be “infected”
in which case they rot. If not infected, their shelf life is still
limited because the enzymes in the fruits and vegetables continue
their catabolic activity in an attempt to release the seeds for
planting and propagation of the species.
Root vegetables are usually hardier than fruit, but if
damaged, they will also spoil due to bacterial and fungal growth.
Because cereals have low moisture content, they keep the
longest; however, in a humid environment, fungal growth can cause
spoilage. Some fungi can produce mycotoxins, which are harmful to
humans.
DEHYDRATION AND SALTING
All living things, including
microorganisms, need water for survival.
Bacteria are especially dependent on an adequate supply of water
because the exchange of nutrients and wastes takes place at the
cell surface. Bacteria, yeasts and molds have a semi-permeable
membrane under the hard, rigid cell wall.
It is with aid of the active transport of water across the
cell membrane that food is taken in and wastes excreted.
In general, only water can move freely in either direction.
Since the microbial cell contains various solutes (salts,
proteins and other molecules), water tends to move from the
surroundings to the cell cytoplasm, to equalize water
concentration on both sides of the membrane.
The constant movement of water to the cell cytoplasm creates a
pressure (turgor) inside the cell, which would easily cause the
cell to expand and eventually burst if it were not for the rigid
cell wall.
Microorganisms will loose water in a dry
environment and although the cell wall may not collapse, the
cytoplasm will shrink. While the metabolism of
such cells has been stopped and the spoilage halted, the cells
will not necessarily die. Upon rehydration of the food product, it
is surprising how many cells will recover.
Rehydrated foods appear to spoil more rapidly than the same
products before dehydration.
The drying process is not linear function.
Initially, water is removed from the food readily.
After the surface water has been removed, the drying rate
slows and depends on the rate of water migration to the surface.
It is therefore not surprising that small food particles
will dry faster than large particles.
Furthermore, dry air will be more effective than moist air, which
already carries a considerable amount of moisture and may not have
the capacity to pick up more water. The drying
rate also depends on air velocity, provided the air used is not
close to the dew point. Increasing the air temperature will
increase the dehydration rate, but one must be careful not to
cause case hardening (formation of a hard, impermeable outer
coating) because that will prevent further removal of water form
the product.
While case hardening may be troublesome in some cases, it is
exploited in others.
Some products are intentionally forced to form a hard,
impervious coating early in the drying process.
As the heating continues, vapor pressure is build up to the
point that the food particles burst open. This action exposes a
large internal area for further drying.
Drying equipment may be batch or
continuous, atmospheric or vacuum. Continuous
drying equipment includes tunnel drying, belt drying, fluidized
bed, drum drying and spray drying. With tunnel drying the hot air
may be introduced into the dryer at the same end as the moist
food, at the opposite end, in the center of the tunnel to exit at
both ends of the tunnel, or it may be introduced at both ends to
exit in the center of the tunnel.
These different combinations have their advantages and
disadvantages, and application depends on the objective and the
product.
At this point it is important to
note that it is not the amount of water that is present in a food
item that determines bacterial growth or survival, rather it is
the availability of water. Water availability
is measured in terms of water activity (aw) and is
obtained according to the formula shown below:
aw = (vapor pressure of food)/(vapor pressure of water)
at the same temperature.
You may have bitten into a slice of bread that was left on the
kitchen table for a few hours during the winter months and been
surprised by how dry its surface was.
Similarly you may have forgotten to tightly close the
cereal package during the warm and humid summer days, and this
negligence resulted in the cereal becoming a little damp and
therefore less crisp.
From these observations, it is apparent that water in our food
will attempt to reach equilibrium with the moisture of the
surrounding air. This principle is used in some of the equipment
used to measure water activity of food.
The equipment is made of a vessel that is filled with food
(leaving only a small head space), sealed hermetically and allowed
to equilibrate. Humidity is then measured in
the headspace and called Equilibrium Relative Humidity (ERH).
The value obtained is divided by ERH of pure water at the
same temperature, giving us the water activity for the food in
question. Since the vapor pressure of water
will always be greater than that for any food, aw will
always be less than 1. 00. Since humidity of air changes with
temperature, equipment that is used to measure water activity is
automatically corrected for temperature, thus providing directly
water activity reading for the food examined.
When drying food, it is important to remember that water activity
of the product does not change linearly with water content of the
product. Such a plot is called Water Sorption
Isotherm. Since relative humidity of air changes with temperature
at the same water content, water activity of a product will change
with temperature at the same water content.
Minimum aw for must bacteria involved in spoilage is
about 0. 90. Halophilic and halotolerant
bacteria (those that multiply in brine solutions of various
concentrations) can grow at water activity close to 0. 75.
Microorganisms that tolerate high salt solutions are
involved in spoilage of pickling brines, while osmophilic
microorganisms are involved in spoilage of products with high
sugar content. Staphylococcus aureus,
which is responsible for “staph” food poisoning, can grow at aw
as low as 0. 88. Clostridium botulinum,
on the other hand, requires a minimum water activity of 0. 90.
Most yeast and molds tolerate lower minimum water activity
than bacteria; they can grow at a minimum aw of 0. 87
and 0. 70, respectively.
We must remember that these values
have been obtained under ideal growth condition, except for
controlling water activity. As conditions
become less favorable for growth and reproduction (drop in
temperature, increased acidity, etc), the above-indicated minimum
aw can no longer be tolerated. The increase in minimum
water activity requirement varies with every environmental
condition.
Adding one solute or another to the food in question to reduce
water activity will control spoilage.
Solutes used in food processing are sugar, salt, glycerol
and other compounds. The addition of sugar is most frequently used
in preventing spoilage of preserves.
Salt is used in the preservation of fish, and a combination
of salt and sugar (as well as nitrites) is used in the
preservation of cured meats. Sugars are known to control bacterial
spoilage through water activity. Sodium chloride exerts an
additional controlling factor on bacterial metabolism besides
reducing water activity. Specifically, excess chloride ion
interferes with the normal function of the cell membrane.
People have known for centuries
that meat, fish, fruits and vegetables can be dried and thus
protected from spoilage. This was usually
accomplished by sun drying. At times it was
noticed that meat and fish would spoil before water was reduced to
the point where spoilage would be prevented.
To assure drying without spoilage, it became routine practice to
salt the tissue before sun drying. Vegetables,
on the other hand, were blanched. Salting of fish reduced
bacterial spoilage and perhaps prevented flies from lying eggs,
and blanching destroyed most microorganisms on the surface of
vegetables and inactivated enzymes that would have remained active
and reduced the quality of the product before water activity was
reduced to a safe level.
Fruits may be treated with sodium sulfite to prevent excessive
browning. Food treated with sulfites must now be labeled because
many people are allergic to such products.
Some foods are cooked. Cooking causes
shrinkage (syneresis) and thus partial “drying”, but such products
are also ready for consumption upon rehydration.
Salting and smoking of fish has changed dramatically during the
last 20 to 30 years.
Although some consumers have retained a taste for salted
fish, others will not purchase it because it must be soaked
thoroughly to remove excess salt. Many
homemakers are not willing to spend the time preparing highly
salted fish for a meal. Consequently,
processors reduced the brine concentration or brining period to
come up with a product that would sell and yet prevent growth of
Clostridium botulinum. This approach
creates problems because at elevated temperatures during the
brining period there will be two competing forces: one is salt
penetration and the other is potential growth of Clostridium
botulinum. Air-drying of inadequately salted products at room
temperature is therefore not allowed.
Salt uptake by fish is controlled
by the brine concentration, size of the fish, and the brining
period. Brine temperature and fat content also
play a role. A study on salt uptake by herring
in refrigerated brine was performed several years ago, but the
results did not yield a simple model that could be used to predict
salt uptake. It is not surprising that salt uptake of intact fish,
even eviscerated, is noticeably slower than for a fillet with
exposed tissue.
Intermediate Moisture Food (IMF) is
a new term but an old technology. In this
group of foods we find products such as raisins, dates, figs and
honey. These products contain a relatively
high moisture level (20% to 50%), which is well above the level
required to prevent microbial spoilage, but less than normally
found in food. These foods do not spoil because solutes are
present that reduce water activity.
New products in this category have added sugar, glycerol,
salt or a combination of these ingredients.
The advantage of such products is that they are moist and ready to
eat without the reconstituting that is necessary for dehydrated foods. Because
of low water activity, packaging is relatively simple and
inexpensive.
The packaging, however, must have a good seal and be
impermeable to moisture. The reason for such
requirements is that IMFs have the tendency to absorb moisture
(they are hygroscopic) from the surrounding air.
As moisture accumulates on the surface of these foods, aw
increases, allowing microorganisms to grow, which leads to
spoilage. Pet food is the biggest
market for these new products.
Smoking used to be a method of food preservation, but because of a
change in consumer preferences, today’s products are different and
must be refrigerated.
Current products cannot be kept at room temperature because
the salt content is too low and the moisture level is too high.
Since the product is smoked, its spoilage will not be by the
Gram-negative bacteria, which produce bad odors.
Instead, mostly Gram-positive bacteria spoil such products,
a group that includes Clostridium botulinum.
Freezing can be considered a form
of drying to control bacterial spoilage, because as water changes
to ice crystals, it is no longer available for bacterial
metabolism. From the aspect of food quality,
slow freezing is not desirable because such freezing causes
formation of large ice crystals that damage the cells of frozen
tissue. Upon thawing the product will have
lost its previous water-holding capacity and tissue “drip” will
have increased. Ice crystal formation is
damaging to bacterial cells, and a noticeable percentage (50% to
90%) of cells will not survive the freezing.
This reduction in bacterial viability, however, is
microbiologically not significant. When thawed this product will
spoil very rapidly.
Cryogenic freezing implies very
rapid freezing. It is the preferred method of
freezing because it results in small ice crystals and a
better-quality product upon thawing. Cryogenic freezing is
accomplished by using liquid nitrogen in a tunnel freezer or
immersion freezing in alcohol at very low temperatures.
Interestingly, a greater number of bacteria survive the
cryogenic freezing process than survive the freezing process in a
deep freezer or blast freezer.
We are well aware that laundry can be dried on
a clothesline in the winter in Maine. Direct change of ice
crystals to vapor is known as sublimation.
This principle is applied to food drying, but to speed up
the sublimation process, the product is placed in a vacuum changer
and heat is applied to the frozen product. As
the ice crystals are converted to water vapor, the space
previously occupied by water remains empty, resulting in a
honeycombed product. While these freeze-dried
products are of highest quality, they are not popular because of
the high cost of processing. It may be worth mentioning that
freeze-drying is not harmful to microorganisms.
In fact, freeze-drying is the preferred method of
preserving bacterial cultures for prolonged storage.
ACIDIFIED FOOD
Fermentation of food, as in the
case of yogurt and sauerkraut production, has been practiced for
many centuries. Although the bacteria
responsible for the fermentation process or their sequence is
different for the two products, the action in both cases is the
same: conversion of sugar to lactic acid. Consequently the
above processes are frequently referred to as lactic acid
fermentation.
For yogurt production, bacteria
responsible for lactic acid accumulation are Streptococcus
lactis and Streptococcus cremoreis.
These bacteria are present in the cow’s udder and are introduced
into the milk at the time of milking. Although other
microorganisms may also be introduced into milk from the
surroundings, streptococci will outgrow all contaminants at
temperatures higher than 50°F, resulting in sour milk.
Sauerkraut fermentation is more
complex from a microbiological aspect. To make sauerkraut, healthy
heads of cabbage are cleaned, the outer leaves are removed, the
core is cut out and the rest is shredded.
The shredded leaves are then tightly packed in a barrel
with between 2% and 3% salt. When the barrel
is full, appropriate weight is used to keep the shredded leaves
covered with exuded liquid. The addition of salt has two purposes:
it extracts tissue juices and it slows down or prevents growth of
Gram-negative spoilage bacteria, allowing lactic acid bacteria to
predominate.
There are three different bacteria
involved in sauerkraut fermentation. The first
bacterium is Leuconostoc mesenteroides, which grows until
it can no longer tolerate the acidic environment it created.
At this point, Lactobacillus brevis takes over the
fermentation process and continues production of lactic acid.
The bacterium Lactobacillus plantarum then completes
the process.
The degree of acidity in such
products is measured in terms of hydrogen ion [H+]
concentration and is expressed as pH. The hydrogen ion
concentration in general is very small.
In water, which is considered neutral, the hydrogen ion
concentration is 0. 000,000,1 G/Liter or 1x10-7G/L.
To simplify the term, the practice is to use the reciprocal
of the logarithm. Thus neutrality is expressed
a pH 7. 0. As acidity increases to 0. 000,001
G/L of hydrogen ion, the pH will be 6. 0. A 0. 1
N solution of hydrochloric acid, which will have a hydrogen ion
concentration of 0. 1 G/L or 1x10-1 G/L, has a pH of
1. 0.
Inorganic acids, such as
hydrochloric acid (HCl), dissociate completely into corresponding
ions [H+] and [Cl-] as compared to organic
acids, which do not. In lactic acid (organic
acid), the molecule dissociates into lactate and hydrogen ions (CH3-CHOH-COOH « [CH3-CHOH-COOH-]
+ [H+]). There are three important
points to remember about organic acids:
1. Organic acids are weak acids; inorganic
acids are strong acids.
2. Organic acids do not dissociate completely;
inorganic acid dissociate completely.
3. Organic acid have a greater biological
effect, inorganic acids have a lesser biological effect.
Interestingly, organic aids inhibit bacterial activity because
the undissociated molecule enters the cell and once inside
dissociates, exerting its effect. Consequently, lower pH
must be employed with inorganic acids to bring about the same
biological effect as with organic acids.
It is important to remember that an acidic environment will
inhibit Gram-negative spoilage bacteria and cells of
Clostridium botulinum. Over the years it
has been observed that Clostridium botulinum will not grow
in an anaerobic environment at pH 4. 6 or lower.
Fermented milk must have a titratable lactic acid
concentration of 0. 85% at which level the pH will be between 4. 4
and 4. 5. The pH of a product will not provide
information on the concentration of the acid; it only provides the
hydrogen ion concentration. The amount of acid in a food product
can be determined by titration.
To illustrate the relationship between pH and titratable
acidity we can examine a 0. 85% water solution of lactic acid.
Such a solution will have 0. 85% titratable acidity (as does
fermented milk), but the pH will be 2. 2. The
difference in pH between the two liquids (water and milk) with the
same lactic acid content (0. 85%) is due to milk’s buffering capacity. All
foods have the capacity to slow down pH drop to a greater or
lesser extent as acids are added.
A good-quality sauerkraut is expected to have a titratable
acidity of 1. 5% - 1. 8% (lactic acid concentration) with a pH
between 3. 2 and 2. 8. In addition to lactic
acid, there may be other acids at low concentrations, but the titratable
acidity is expressed in terms of lactic acid equivalent.
Neither yogurt nor sauerkraut has an indefinite shelf life.
The culture responsible for acid production begins to die
off after having reached the maximum stationary phase.
Other microorganisms, such as yeasts and molds, that were
present but could not compete with the lactic acid fermenters,
begin to use the acid for their metabolic activity.
As time passes, the quality of the fermented product
deteriorates, and eventually it is considered unacceptable for
consumption.
While yogurt is consumed only as a fresh product, sauerkraut
can be heated to >165°F,
placed in a can, which is sealed while hot after going through an
exhaust box. It is recommended that the can be
inverted after sealing to assure contact of the product with the
lid. Hot organic acid damages most
microorganisms, including those that produce it in the first
place. Thus all vegetative cells that may be present in the
fermented sauerkraut will be killed.
Only spores of various bacteria, including those of
Clostridium botulinum, will survive.
Although canned sauerkraut is in an anaerobic environment, the
spores of Clostridium botulinum will either not germinate
or if they do germinate, the vegetative cells will not be able to
grow and reproduce if the pH is 4. 6 or lower. Consequently,
this can be called a “commercially sterile” product, in other
words, a product that will not spoil at room temperature.
It is important to remember that the controlling factor of
pH 4. 6 is so important that food with pH greater than 4. 6 are
classified as low-acid food, and those with pH 4. 6 or lower, as
acid food.
Although food can be preserved for a period of time by
fermentation, the same preservative effect can be obtained by
adding such acids as lactic, acetic, or other acids and lowering
the pH to the level that will result in the desired product with
an extended shelf life. The best-known product
in this category is relish, although it is perhaps not recognized
as an“acidified food. ”
Processing of acidified food is well defined, but because
botulism is an associated hazard, FDA regulations 21CRF Part 114
deal with this subject in considerable detail.
Fruits are acidic (pH < 4. 6), while most vegetables, meat,
poultry, and fish are close to neutral.
However, only fruits and tomatoes have pH <4. 6.
Acidified food, according to FDA regulations, is low acid
food with aw > 0. 85 to which acid or acidified
food has been added, reducing pH to < 4. 6.
Carbonated beverages, jams, jelly, and preserves are
excluded from FDA regulations 21CRF114.
Production of acidified foods must meet current Good
Manufacturing Practices (cGMP). The food may
not be adulterated. Production of acidified
food may not be “prepared, packed, or held under unsanitary
conditions whereby it may have become contaminated with filth, or
whereby it may have been rendered injurious to health. ”
Personnel processing and packing acidified food must be under the
supervision of a person who has attended an approved school.
Such a school must provide “instructions in food-handling
techniques, food-protection principles, personal hygiene and plant
sanitation practices, pH control, and critical factors in
acidification. ”
The manufacture of acidified food requires that the finished
product not present to the consumer a health hazard.
The product must have a pH of 4. 6 of lower, which must be
reached within a time period of the approved schedule process.
“Acidified food shall be heat processed to destroy
vegetative cells of microorganisms of public health significance”
and spoilage flora that could shorten shelf life under normal
handling and retailing.
To assure an equilibrium pH of not higher than 4. 6, the
measurements of acidity before and after equilibration may be
performed using a pH meter. If the
equilibrated product pH is 4. 0 or less, then colorimetric tests
may be used. If lye (sodium hydroxide) is
used in the peeling process, special precautions must be taken to
ensure that none was carried over into the product, since lye will
neutralize the acids that are needed to acidify the food
Procedures used to
acidify low acid foods include the following (see 21CRF114):
- Blanching of the food ingredients in acidified aqueous
solutions.
- Immersion of
the blanched food in acid solutions. Although immersion of
food in an acid solution is a satisfactory method for
acidification, care must be taken to ensure that the acid
concentration is properly maintained.
- Direct batch acidification, which can be achieved by
adding a known amount of an acid solution to a specified amount
of food during acidification.
- Direct addition
of a predetermined amount of acid to individual containers
during production. Liquid acids are
generally more effective than solid or pelleted acids.
Care must be taken to ensure that the proper amount of
acid is added to each container.
- Addition of acid foods to low-acid foods in controlled
proportions to conform to specific formulation.
During production, every individual container must be coded.
The code must be affixed in such a manner that it cannot be
easily removed. The code must identify where
the product was packed, what food was packed, and the year, date
and period of day it was packed. The code must
be changed every 4 to 5 hours, or for every personnel change, or
for each batch of food processed. Records must
be kept for at least three years. Contingencies must be
developed in case a recall is required.
For the recall to be effective, a plan must be in place and
tested periodically. Before a recall can be
initiated, the FDA (see 21CRF7C) requires the following
information:
-
Identity of the product involved.
-
Reason for the removal or correction and the date and
circumstances under which the product deficiency was discovered.
-
Evaluation of the risk associated with the deficiency or
possible deficiency.
-
Total amount of the product and/or the time span of the
production.
-
Total amount of the product estimated to be in distribution
channels.
-
Distribution information, including the number of direct
accounts and where necessary, the identity of the direct
accounts.
-
A copy of the firm’s recall communication if any has been
issued, or a proposed communication if none has been issued.
-
Proposed strategy for conducting the recall.
-
Name and telephone number of the firm’s official who should be
contacted concerning the recall.
Hydrogen ion concentration of a product is determined with a
pH meter. This is an
instrument that measures the potential between the glass
and a reference electrode. Such electrodes are
now available as a single probe, which makes the instrument easier
to handle. There are also battery-operated,
hand-held pH meters with electrodes protected with a plastic cover
to minimize breakage of the glass electrode. Stainless steel
electrodes are now available.
The operator
must be thoroughly familiar with the operating instructions before
taking a measurement. Before each use, the
instrument must be standardized with buffered solution at pH 4. 0
and pH 7. 0. This standardization must be
performed at the beginning of production testing and at frequent
intervals thereafter. The product must be at
room temperature when tested. Between samples,
the electrodes must be thoroughly rinsed with distilled water and
blotted with soft tissue, but not wiped. When examining oily
products, the electrodes should be cleaned with diethyl ether, and
the instrument must be frequently standardized.
Whenever the
product consists of two phases, liquid and solid, these must be
examined separately. The solid portion should
be rinsed with distilled water and homogenized, and the pH of the
paste determined. If there is too little
moisture in the paste, 20 ml of distilled water may be added to
100 g of the paste. The pH of the liquid and
solid phase must be within 0. 1 pH unit of each other.
For example, if the liquid pH was 3. 5, the solid pH must be
between 3. 4 and 3. 6. Oil phase, if present, must be removed and
pH of the aqueous portion determined.
Records must be kept of every process step during
acidification. Whenever deviations from
approved process operation occur, they must be recorded, including
the equilibrium pH. If the equilibrium pH of
the product is higher than 4. 6, the product must be (a) fully
reprocessed, (b) thermally processed as low-acid food, or (c) set
aside for evaluation by a competent processing authority as to any
potential public health risk. Subsequent to that evaluation, the
product may be recommended to be reprocessed or to be destroyed.
THERMAL PROCESSING
People have cooked food ever since they learned how to handle
fire, but it was not until 1810 that Nicholas Appert showed that
cooked food can be preserved for a longer period of time than raw
food. He accomplished this by using excellent
quality raw material, which was cooked for a prolonged period and
then carefully sealed. The phenomenon was not
explained until 1864 when Louis Pasteur showed that spoilage is
due to living “creatures” floating in air.
John Tyndal later demonstrated that dust carried the “germs”.
Pasteur was
also instrumental in helping his neighbors to consistently produce
good quality wine and beer. He noticed that
good quality product had one type of microbes and poor quality had
another type. Through experimentation, Pasteur found that he could
destroy most of the microbes that were present in the liquid by
holding it at 145°F for 30 minutes without altering the quality of
the liquid.
Then he would add some good quality wine or beer to the
liquid, thus assuring that the new product would be of acceptable
quality.
Canning, as we know it today, was developed when a retort
(pressure cooker) was invented in 1860. This equipment made use of
steam under pressure, allowing heating of canned food to 250°F.
Improvements in can construction also made
canning easier. Early cans were metal
containers with a hole through which food was stuffed into the
can. After the can was heat processed, a lid
was soldered on. A three-piece can was
introduced in 1900, where only the side seam of the round body was
soldered. The bottom and top lids were attached by rolling the
ends to form a double seam.
Since the food was sealed before the can was heat processed
and consequently the food was not exposed to contamination after
processing, the can was referred to as a sanitary can.
Today, the two-piece can is widely used.
Spoilage and presence of toxin in cans plagued the industry
until the 1920s when characteristics of Clostridium botulinum
and its toxin were understood. This led to
a defined procedure to determine process time aimed at the
destruction of the spores of this bacterium
At this time it is important to stress that Clostridium
botulinum Type A, B and E will grow and produce botulinum
toxin in a product if the environment is anaerobic (absence of
oxygen), if the temperature of storage is higher than 40°F (for
Type E) or 50°F (for Types A and B), and if the product is a
low-acid food.
All three requirements are met whenever we attempt to
preserve string beans, chicken, fish, or meat by boiling it in a
glass jar, sealing it and storing it in a pantry.
To safely can these sorts of food at home, a pressure
cooker must be used. Normal boiling will reach at
best 212°F.
Such temperatures will destroy most vegetative bacterial
cells, especially the Gram negative ones, but they will not
destroy bacterial spores. Boiling is frequently used by many
researchers to stimulate spore germination.
Normal cooking or boiling of food has many beneficial aspects.
In most instances the food becomes more palatable and
digestible. Boiling temperatures will destroy
the toxin of Clostridium botulinum, but it will not destroy
the toxin (enterotoxin) produced by Staphylococcus aureus
or those produced by fungi (aflatoxins).
Boiling of drinking water is recommended whenever water cannot be chlorinated. Such boiling will destroy
food-poisoning bacteria that may be present, as well as viruses
and parasites. The destruction rate of bacterial cells in water is
much faster than when the same microorganisms are suspended in
milk or other foods.
Foods offer protection, in fact differences in heat
sensitivity can be observed between different foods.
While some foods spoil faster after cooking, others spoil
slower. Vegetables have natural antibacterial
properties, which slow down bacterial growth.
Cooking destroys these properties allowing contaminants to grow rapidly. Boiling milk, on the other hand,
definitely extends its keeping quality because most of the
vegetative bacterial cells will be destroyed, and the contaminant,
if introduced at lower concentrations than the initial flora, will
reach the spoilage level significantly later. With cooked
products, however, one must be careful to prevent contamination
with pathogens because these might multiply rapidly, having only
few if any competitors.
Pasteurization, as applied to the production of wine and beer,
was soon adapted to the treatment of milk. The
objective was to destroy Micobacterium tuberculosis (TB
bacillus), which was a very serious illness among children.
Pasteurization requires heating milk to 145°F and holding
it at that temperature for 30 minutes.
Subsequently, efficient heat exchangers were built, where
the temperature of milk could be raised to 161°F very quickly and
after 15 seconds the temperature could be brought down to 50°F or
lower.
The critical factor that had to be met was to assure that
every milk particle received this heat treatment.
Enforcement of milk pasteurization eliminated transmission
of tuberculosis from animals to people. It was
subsequently realized that an additional benefit from
pasteurization was the destruction of other pathogens, such as
Streptococcus pyogenes, Brucella abortus, Staphylococcus aureus,
as well as any spoilage bacteria that were introduced at milking.
Consequently, the product had a longer shelf life and was
safe. Now it is recognized that other food
pathogens, such as Listeria monocytogenes, Campylobacter jejuni,
and Yersinia enterocolitica are also destroyed by
pasteurization.
In the mid-Atlantic region, pasteurization of blue crabmeat
was considered economically desirable to extend its refrigerated
shelf life and expand its market. If
pasteurization treatment (time-temperature treatment) were similar
to that of milk, the product would indeed have significantly
longer shelf life than the unpasteurized material.
But while such treatment destroyed Gram-negative bacteria,
it would not destroy spores of Clostridium botulinum Type
A, B, or E. Although survival of
Clostridium botulinum Type A and B spores pose no threat in
refrigerated crabmeat, because the vegetative cells do not grow at
temperatures below 50°F,
survival of Clostridium botulinum Type E spores was
considered dangerous because its vegetative cells will grow at
temperatures as low as 40°F.
To avoid the possibility of Clostridium botulinum
Type E toxin production in a refrigerated crabmeat product, a
pasteurization process was developed to destroy the spores of this
bacterium. In 1970 such a process was developed for one-pound
containers of crabmeat.
Hermetically sealed cans were immersed in water bath at 192°F
for 115 minutes and then cooled in an ice water bath before
refrigeration. With this pasteurization process, the product was
safe under existing storage conditions, and its sensory quality
was no different from the freshly picked crabmeat.
It is important to point out that thermal destruction of
microorganisms at a given temperature has a logarithmic
relationship to the treatment period. Once
such data is experimentally generated, it is possible to select a
time-temperature treatment that results in a safe product while
retaining the desired sensory quality as well as can be
accomplished with available equipment. Heat
sensitivity of Listeria monocytogenes in smoked shrimp and
other smoked seafood products were generated in our laboratory.
Such information is essential when planning to pasteurize
smoked seafood with the intent of destroying Listeria
monocytogenes cells. Permission to place such a product on the
market must be obtained from FDA.
In food service establishments, especially the cafeteria
style, food is held hot or cold, depending on the nature of the
food, and served to the customer. The food in
the serving tray may last several hours.
During this period, especially at elevated temperatures, bacteria
can multiply rapidly. The generation time may
be as short as 10 to 15 minutes. This includes not only spoilage
bacteria but also food borne pathogens.
At low temperatures the replication rate will be
significantly slower; however, even as few as four generations
during the food serving period will increase the population 16
times. Thus a population of food borne pathogens, too few in
numbers to cause an infection, would increase to an infectious
level after four generations.
In order to prevent such situations, the food that is held
in serving trays ready for serving must be at either 140°F or
higher for hot foods, or 40°F or colder for cold foods.
The same principle is applied to chowders that are cooked in
batch volumes. This food must be chilled to
below 60°F within three
hours of finishing the cooking, before it can be placed in a
refrigerator. State regulations require that
food must be chilled from 140°F
to 40°F within four
hours. It is important to remember that large
volumes of food do not cool rapidly, even when placed in a
refrigerator. In fact, it may not be desirable to place a large
pot of hot food in a refrigerator since it may cause the
temperature of the refrigerator to rise.
Consequently, as much heat as possible should be removed
from such food before placing the container in the refrigerator.
This can be accomplished by placing the container in a
cold-water bath (preferably with ice) and stirring it at intervals
to speed up the cooling process. Ice has a good capacity for fast
cooling because one pound of ice at 32°F will absorb 144 BTUs when
changing to water at 32°F.
When discussing cooking, we must be aware that the core of the
food particles heats significantly slower than the surrounding
liquid. It has been reported that Listeria
monocytogenes survived five-minute boiling inside shrimp
tails. It is important to note that the
pathogen was not detected immediately after the boiling, but was
detected when the shrimp tails were analyzed after three days of
refrigeration. The delayed recovery of
Listeria monocytogenes from shrimp tails is important to note
because it implies that the few surviving cells that had sustained
sub lethal damage during processing could (given three days to
recover) repair the damage that was sustained during the boiling
step. This recovery is not surprising since
shrimp is a nutritious product, which will support bacteria
growth. There is nothing wrong with cooking
and refrigerating shrimp on one day and serving it on another day
in a salad. Although we may not often
experience situations where shrimp tails carry as many Listeria
monocytogenes cells as were injected in the experiment, we
should be aware that we must not skimp on the cooking process
(time-temperature treatment). Sub lethal damage is something that
the food processing and food service industries should keep in
mind.
FOOD BORNE ILLNESS
Food borne illness is estimated to afflict 10% of the
population annually. Estimates have placed the
annual cost of treatment and work hours lost at more than $3
billion. When we discuss food poisoning, we must distinguish
between food intoxication and food infection
|
Food
Intoxication
Clostridium botulinum
Clostridium perfringens
Bacillus
cereus
Staphylococcus aureus
Aspergillus sp. |
Food Infection
Listeria
monocytogenes
Vibrio
cholerae
Vibrio
parahaemolyticus
Vibrio
vulnificus
Salmonella sp.
Shigella sp.
Escherichia coli
Yersinia
enterocolitica
Campylobacter jejuni
Plesiomonas shigelloides |
Clostridium botulinum
The most debilitating and
life-threatening food intoxications can result after ingesting
preformed toxin that is produced by Clostridium botulinum.
There are two other forms of botulism: wound infection and
infantile botulism (children under the age of one year).
C. botulinum is
divided into seven groups (A, B, C, D, E, F, and G), based on the
serological characteristics of the neurotoxin the culture
produces. The food industry, however, is
primarily concerned with Types A, B, and E. There were some
200 known outbreaks of botulism in the early 1900s, of which 10%
was due to commercial products.
The botulinum toxin is lethal in very small quantities; one
tablespoon of pure botulinum toxin potentially could cause the
death of about 2x109 individuals.
Home-canned string beans and other vegetables were the most
frequently implicated foods, but home-canned meats and fish were
also involved. More recently, products such as foil-wrapped baked
potatoes, sautéed onions, garlic in oil, and fermented green
peppers were involved in cases of botulism.
Symptoms appear in 12 to 24 hours after a meal, but may
vary from a few hours to several days.
Initially, there may be some vomiting and perhaps diarrhea, but no fever. Symptoms include blurred or double
vision, difficulty in swallowing and speaking and loss of muscle
coordination. The patient will be conscious to the very end, and
death is due to respiratory failure.
The only effective treatment is injections of polyvalent
antiserum. In the past, the mortality rate was 50% or higher, but
in recent times it has dropped to about 10%.
C. botulinum is a motile, Gram positive, anaerobic,
spore-forming rod. This bacterium can be
controlled through temperature, pH, aw, and salt (see
Table 1).
There were about 50 known botulism outbreaks due to acidified
food with pH < 4. 6. In some instances in the
incriminated food, acid-tolerant microorganisms (yeast and molds)
were detected. Consequently, it is suspected
that C. botulinum must have grown in close proximity to the
acid-tolerant mold, where the pH may have been as high as 7. 0, or
the product was not equilibrated. Food
processors, therefore, must take every precaution to prevent the
existence of microenvironments in their products where botulinum
toxin could be produced.
Nitrites are used in cured meats to prevent botulinum toxin
development. Dairy products are not known to
be involved in botulism outbreaks. This is
probably due to the competing lactic acid bacteria (Lactobacillus,
Pediococcus, Streptococcus) producing an acid environment as
well as such compounds as nisin and pediocin. Smoke is
considered by some investigators to have little effect on toxin
accumulation, while other researchers have reported significant
inhibition.
Table 1. Means of controlling growth and
toxin production C. botulinum.
|
Factors |
Type A
& B
(proteolytic) |
Type B
& E
(non-proteolytic) |
|
pH
NaCl
aw
Temperature |
4. 6
10%
0. 94
50°F |
5. 0
5%
0. 97
38°F |
C. botulinum Type A spores
predominate in western U. S. soil. Other areas
primarily have proteolytic Type B spores, while coastal areas and
areas near large freshwater lakes tend to have Type E spores.
Although the spores of Type A and B are more heat resistant
(D10 at 225°F
is about 5 min) than Type E spores (D10 at 176°F
is about 5 min), the botulinum toxin is heat labile (20 min at
176°F or 5 min at 185°F).
Clostridium perfringens is
responsible for food intoxication, but the conditions leading to
the intoxication are somewhat complicated. Meats, stews,
sauces, meat pies, and casseroles are involved.
During cooking oxygen is driven off and while vegetative
cells may be destroyed, the spores not only survive, but are
stimulated to germinate. As the food passes
though temperature ranges at which the bacterium can grow, during
refrigeration and later during reheating, this bacterium can grow
rapidly, reaching very high numbers (1x106 or more/G).
When ingested, the stomach acids may be neutralized by the
food, allowing the vegetative cells to survive.
As the food enters the small intestine, the cells begin to
multiply and sporulate. The sporulating cells
lyse, releasing an enterotoxin.
The incubation period is about 13
hours, but it can be shorter or longer.
Symptoms include diarrhea, abdominal cramps as well as headache
and nausea. Some patients may develop a fever, pass bloody stools,
vomit, or experience dizziness.
Younger patients have milder symptoms than older patients.
C. perfringens is a Gram positive, anaerobic,
non-motile, spore-forming rod.
It is found in soil, thus is easily introduced into food.
Its growth range is between 60 and 126°F,
with a very short generation time (about 10 minutes) at higher
temperature limits. The pH growth range is
between 6 and 7 and aw between 0. 95 and 0. 99.
Bacillus cereus causes two types of gastroenteritis,
depending on the type of food involved.
This bacterium when found in meats, vegetables and sauces
results in stomach cramps, profuse watery diarrhea, and sometimes
nausea and vomiting. Incubation period is 12
to 24 hours. When it is found in rice, on the
other hand, it results in nausea and vomiting 1 to 5 hours after
ingestion, but sometimes vomiting is followed by diarrhea 6 to 24
hours after ingestion. Two types of toxins
cause these symptoms. The diarrheal
enterotoxin is heat sensitive, while the emetic (vomiting) toxin
is heat resistant. Recently food infections involving this
bacterium have been reported. Such
outbreaks were associated with a high number of B. cereus
cells (> 1x105/G), implying the food must have been
temperature abused.
This bacterium is motile, Gram
positive, aerobic, spore-forming rod. It is found in most soils,
thus it has easy access to food.
This bacterium can be controlled by keeping food colder
than 50°F or warmer than 131°F.
Listeria monocytogenes has
been known since the early 1900s to cause infections, but it was
not until quite recently that it was involved in food borne
infections. The first outbreak occurred in
1981 in Nova Scotia. The incriminated food was
coleslaw. Cabbage used for the coleslaw came
from a farm where a few sheep had died of listeriosis.
There were 34 cases in this outbreak, all pregnant women.
These cases ended in abortion, stillbirth, or serious
infection of the newborn. The second outbreak implicated
pasteurized milk in Massachusetts in 1983.
There were 49 individuals involved with compromised immune
system, of whom seven were pregnant women. The
third outbreak took place in California in 1986 and involved 86
individuals, half of whom were pregnant women.
The implicated product was Mexican-type soft cheese. In all
three cases, serotype 4b was involved.
From this information, it is clear
that persons with suppressed immune systems, including pregnant
women, are susceptible to the infection. Healthy individuals
only experience flu-like symptoms, severity depending on the
individual’s resistance and the number of microorganisms involved.
L. monocytogenes is widely
distributed in nature. It has been found
associated with cattle, poultry, and birds. As many as 25% of
seagulls are suspected of excreting this bacterium.
This bacterium will persist in soil and in water, but the
greatest danger is that it will grow at temperatures as low as
32°F.
In some foods at 43°F, it has been found to double in
number every 24 hours, while at 32°F, it may double every seven
days.
This bacterium is heat sensitive
and readily destroyed by pasteurization, but because it is so
widely distributed in nature, it is frequently reintroduced into
cooked foods. The probability of this
bacterium being present in crabmeat is high, because crab picking
requires extensive handling. Strict sanitation
practices are essential to assure the absence of L. monocytogenes
in all ready-to-eat foods.
L. monocytogenes is a Gram
positive, motile, facultative, halotolerant, nonsporing rod.
Since it is a psychrotoroph, growing at 32°F, its control
presents a serious challenge.
It has been known for years that
Staphylococcus aureus causes food intoxication.
This bacterium produces 6 serologically different
enterotoxins (A, B, C, D, E, and F), which are heat resistant.
Meats, especially cured meats, barbecued chicken, various
salads, and bakery products with custard or cream fillings are the
types of foods involved. In such cases the
food is temperature abused, allowing S. aureus to grow,
reaching numbers greater than 1x105 cells/G.
These foods tend to have lower aw values (0. 90 –
0. 95), giving this bacterium an advantage over the Gram-negative
spoilage flora.
Symptoms usually appear in two to five hours after a meal, but
they may appear sooner.
The patient will experience nausea, vomiting, abdominal
cramps, and diarrhea. The illness is
self-limiting within a day or two and not fatal, unless
complications arise. Severity of the symptoms depends on the
amount of toxin ingested and the individual’s resistance.
S. aureus is a Gram
positive, facultative coccus, forming a cluster of cells on a
microscopic slide. Growth and toxin production
can be controlled with proper refrigeration (<50°F), hydrogen ion
concentration (pH <4. 6), or water activity (aw <0.
85).
The source of this bacterium is human carriers and minor
infections, such as pimples, and boils.
Carriers, who can represent 25% or more of the population, will
have this bacterium in the nasopharynx.
Vibrio cholerae causes very
severe diarrhea (watery stool), resulting in dehydration, loss of
electrolytes, shock, and death within days.
Symptoms appear within one to two days.
Treatment requires antibiotics and the replacement of lost fluid
and electrolytes. Two serogroups are known to be involved: 0:1 and
non 0:1. Both serogroups are found
in brackish waters, estuaries, and coastal marshes.
The organism is transmitted by polluted water and can be
carried by vegetables and other foods that are not cooked.
Sporadic cases occurred in the U. S. from people
eating inadequately cooked crabs or raw oysters.
This bacterium is a Gram negative, comma-shaped, motile (single
polar flagellum), aerobic rod.
Vibrio parahaemolyticus does
not cause nearly as severe an illness as its cousin V. cholerae;
it will, however, cause diarrhea, abdominal cramps, nausea,
vomiting, and to lesser extent headache, chills, fever, and bloody
stool. As late as 1968, this organism was not recognized as
causing digestive tract disturbance, but in 1971 there were 370
reported cases and in 1972 there were 701 cases.
Annually there appear to be two or three outbreaks.
Foods involved include crabmeat, processed lobster, boiled
shrimp, cooked oysters, and raw oysters.
Incubation period is 12 to 24 hours, but exceptions frequently occur. Infectious level is thought to be 1 x
105 cells.
This is a marine organism, growing well in the
presence of 1% to 3% salt. Its growth range is
50 to 109°F, minimum aw of 0. 94, and pH range 5 to 11.
The bacterium is Gram negative, straight or curved, motile,
facultative rod. Although the cells are sensitive to low
temperatures, salt appears to protect the cells from damage.
Vibrio vulnificus
Vibrio vulnificus was recognized initially in the 1970s
as causing frequently fatal wound infections.
Since then it was noted that this bacterium is a marine
organism that is different from V. cholerae and V. parahaemolyticus,
living in estuarine waters.
Ingestion results in an infection and septicemia with 60%
mortality. Symptoms include fever, chills, nausea, vomiting,
abdominal cramps, and diarrhea.
Incubation period is 12 hours to several days.
Raw shellfish, particularly oysters have been implicated in
outbreaks.
The bacterium is sensitive to cold
temperatures, becoming non-culturable when exposed to 39°F.
It is Gram negative, straight to curved, motile (single
polar flagellum), aerobic rod. Growth has been observed at 77 to
104°F.
Salmonella sp.
Salmonella sp. have been known since the
late 1800s to cause “hog cholera”, which was transmittable to people. The illness is an infection due to the
ingestion of live Salmonella cells. The
incubation period may be 14 hours, but may be shorter or longer
depending on the number of cells ingested, virulence of the
serovar, and natural resistance of the individual.
Symptoms include diarrhea, abdominal cramps, fever, nausea,
and vomiting. Infection depends on the
virulence of the serovar. Most serovars are very invasive and upon
entering the blood stream can cause an infection of any internal
organ.
Annually there are about 60 outbreaks with
2,500 cases and 10% mortality due to Salmonella infections.
The microorganism gains entry to food from persons
recovering from an illness, who show no symptoms and feel
absolutely healthy, but are still shedding the bacillus.
There are also healthy carriers who have no symptoms, but
harbor the microorganism in the gall bladder duct, shedding
Salmonella cells intermittently. The third
source is poultry and contaminated eggs.
Carriers can be cured with prolonged antibiotic treatment, but
similar success has been achieved by drinking fermented milk
containing live Lactobacillus acidophilus.
The initial contamination level of food need not be high to
cause an outbreak, since this microorganism will grow in most
foods at temperatures between 50 and 117°F.
There are some serovars that will grow at temperatures as
low as 41°F. The food itself exerts some
effect on the growth of this pathogen. For
example, while Salmonella enteritidis and Salmonella
manhattan did not grow in custard or ham at 39 to 50°F, they
did grow at 44°F in chicken-a-la-king.
The pH range for these microorganisms is
between 4. 5 and 9. 0, but minimum pH will depend on the nature of
the acid used. Growth occurred at pH 4. 05 when HCl or citric acids were the acidulants, pH 4. 40 when lactic acid
was used, and pH 5. 40 when acetic acid was employed.
Salmonella cells require relatively high water
activity for growth, with aw 0. 92 being the lower
limit.
There are some 1,700 serovars that are
distinguished from one another by serology (specific
antigen/antibody reaction), biotyping (substrate utilization),
phage typing (susceptibility to virus destruction), colicin typing
(proteinaceaous bactericidal compounds produced by Escherichia
coli), and plasmid fingerprinting (electrophoresis of
extracted plasmids). These serotypes, when
isolated from major outbreaks and found to be distinct from
previous serovars, are usually given the name of the
location where the outbreak occurred.
The more useful characterization of a serovar is the plasmid
fingerprinting since the plasmids determine antibiotic resistance,
substrate utilization, adhesion to surfaces, ability to form pilli,
and so on. A very useful observation is that
only certain plasmids will coexist in a cell. The bacillus
is a Gram negative, motile or non-motile, aerobic rod.
Shigella sp.
Shigella sp. is responsible for
bacillary dysentery, where in severe cases the stool contains
blood and mucus. Outbreaks involving this
microorganism are primarily a problem in crowded urban
institutions. There are several species in this group that cause
varying degrees of dysentery.
Transmission is from person to person or by contaminated
salads. The incubation period is from 14 hours
to a few days. Symptoms are primarily diarrhea and abdominal
cramps.
This microorganism is a Gram negative,
non-motile, facultative rod. Upon ingestion, it will travel to the
small intestine where it attaches itself to epithelial cells,
causing ulceration.
Escherichia coli
Escherichia coli is the predominant
microorganism of the normal flora in the intestine of a
warm-blooded animal. Because of this
association, E. coli is used as an indicator of fecal
pollution of drinking water. It is also used
as an indicator of fecal contamination of clam flats and for that
matter any food product. This bacterium was
not considered a pathogen, even as it appeared in increasing
numbers of urinary tract infections. This microorganism is Gram
negative, motile, facultative rod.
It will not grow at a minimum temperature of 46°F, in a
maximum salt concentration of 8%, and a minimum pH of 5. 6.
More recently it was noticed that E. coli
could cause four different syndromes of gastrointestinal
disturbance. It is now known that there are
four distinct types: (a) enteropathogenic (EPEC), (b)
enteroinvasive (EIEC), (c) enterotoxigenic (ETEC), and (d)
enterohemorrhagic (EHEC).
There are 15 different serotypes in the
entropathogenic group, having distinct O antigen.
This group of fecal coliforms causes infantile diarrhea and
is associated with fever, vomiting, and abdominal cramps.
Food-transmitted EPEC also causes nausea, vomiting,
diarrhea, abdominal cramps, headache, fever, and chill in adults.
The stool is watery but without blood.
Incubation period is from 12 hours to 3 days, and the infectious
dose is 1 x 106 or more cells.
The enteroinvasive group causes dysentery type
symptoms, resembling those of Shigella infection.
These symptoms are the result of the bacterium invading the
epithelial mucosa of the intestine. Incubation
period is 8 to 24 hours. Outbreaks occurred in hospitals where
mothers and their babies developed the infection.
Similar outbreaks occurred on cruise ships, where the
incriminated food was cold buffets. There are nine serotypes in
this group with different O antigen and all are non-motile.
The entrotoxigenic group is primarily known as
travelers’ diarrhea. The initial outbreak
appeared to be due to O148:H28 serotype, but now there are at
least 17 serological (O antigen) serotypes in the ETEC group.
The microorganisms produce two toxins: (a) heat-sensitive
enterotoxin that is related to cholera toxin, and (b)
heat-resistant, non-antigenic enterotoxin of small molecular size.
The incubation period is about 24 hours, but could vary
from a few hours to two days. The infectious
dose is 1 x 108 or more. Symptoms include watery
diarrhea, fever, nausea, and abdominal cramps.
The enterohemorrhagic E. coli is
represented by a single serotype: O157:H7. This
microorganism is responsible for at least three different
syndromes.
1.
Hemorrhagic colitis involves sudden sever stomach
cramps, which are followed a day later by watery, grossly bloody
diarrhea. Some patients may vomit, but none
develop fever. The incubation period is about 5 days, and the
illness may last from a few days to a couple of weeks.
2.
Hemolytic uremic syndrome results in kidney failure, primarily in
children.
3.
Thrombic thrombocytopenic purpura involves the nervous system,
causing blood clots in the brain.
Mortality rate is high with EHEC.
Yersinia enterocolitica
Yersinia enterocolitica was initially
noticed by investigators examining children with enteritis in the
early 1940s. By 1980 several thousand isolates
were obtained from adults and chinchillas. Symptoms in
people include fever, abdominal cramps, and diarrhea.
Septicemia was reported with healthy infants and adults
with predisposing illnesses (diabetes and pneumonia).
This microorganism can cause other infections, such as skin
infection, eye infection, endocarditis (heart valve infection),
thyroid disorder, glomerulonephritis (kidney inflammation), liver
disease, respiratory infection, and muscle abscesses.
The first reported case involved a person who
drank from a mountain stream. Cats and dogs were found to
harbor this microorganism, along with wild animals and rodents.
From very early on it was suspected that food was the
transmitting medium.
The microorganism is a Gram negative, motile,
aerobic rod. It will grow best at room
temperature, but also will grow at 39°F. The
pH range for this bacterium is 6. 8 to 9. 0. Two
other species that can also cause similar symptoms are Y. pseudotuberculosis and
Y. pestis.
Campylobacter jejuni
Campylobacter jejuni causes acute
gastrointestinal infection. This microorganism
was first recognized in 1938 as causing infectious infertility and
abortion in sheep and cattle. In 1938 two
outbreaks of acute gastroenteritis occurred involving 151 persons
in two prisons. Symptoms include diarrhea, vomiting, abdominal
cramps, headache, and fever.
As time passes, the stool becomes watery and later bloody.
Incubation period is 2 to 5 days, and illness may last one
week.
The microorganism is Gram negative,
microaerophilic, slender, curved, motile rod.
Temperature growth range is between 77 and 109°F and pH range is
5. 5 to 8. 0. Foods involved include milk,
poultry, eggs, pork, and beef. The bacterium
appears to be spread by the food handler, while the source may be
healthy or sick cats and dogs. Wild birds are
suspected of being the source of C. jejuni in fresh
water.
Plesiomonas shigelloides
Plesiomonas shigelloides has been involved
in several outbreaks of gastroenteritis.
Symptoms include nausea, vomiting, fever, chills, headache, diarrhea. Incubation period is about 1 to 2
days. Raw oysters, salted fish, and cooked
crabs have been implicated in infections. In one outbreak, 275
individuals become ill after eating fish salad.
The source of this microorganism includes freshwater fish,
reptiles, crustaceans, mammals, and birds.
The bacterium is a Gram negative, facultative, halotolerant,
motile rod. It can grow between 46 and 122°F
and pH 4. 0 to 9. 0. It has also been observed to grow in nutrient
medium in presence of salt to 3% concentration.
SANITATION AND GMP
At the turn of the 19th
century, many changes were taking place that had effects on the
way food was processed. As mentioned earlier,
it was around this time that it was recognized that bacteria were
responsible for food spoilage. At the same time, Koch’s postulates
were confirmed, showing that specific microorganisms were the
cause of specific diseases.
Closer examination of foods by the United States Department
of Agriculture (USDA) revealed good correlation between
cleanliness of processors and the microbiological quality of their
products. These observations lead to the Meat Inspection Act and
the Food and Drug Act of 1906.
Since the associated regulations were not effective, a bill
was passed in 1938 known as the Federal Food, Drug and Cosmetic
Act. While initial concern was filth in food, subsequent
activities included microbiological safety.
A food plant sanitation program has no chance
of being effective unless there is commitment from management and
the manufacturing personnel. This also applies to foodservice
establishments, where conditions are more crowded and an
individual employee’s habits have greater effect on the quality of
the product.
Training films on sanitation and public health
are available for staff from trade associations and government
agencies. A good food processing or
foodservice operation is effective if the facilities are designed
with sanitation needs in mind. At times
modifications must be made after construction to meet sanitation
needs, but it should be realized that such modifications are
usually more expensive than when these needs are addressed at the
time of planning and construction. The
management must address these concerns. It is also important to
keep in mind that if regulatory agencies find unsanitary practices
in a food processing or foodservice operation, the management is
held responsible and could be charged in certain cases with
criminal acts.
Good Manufacturing Practices (GMP) provide
guidelines under which food may be prepared for sale to the
general public (see
http://www. cfsan. fda. gov/~lrd/part110t.html).
Under these guidelines, food that “has been manufactured
under such conditions that it is unfit for food or … that it has
been prepared, packaged or held under unsanitary conditions
whereby it may have become contaminated with filth, or whereby it
may have been rendered injurious to health” (21CFR110) is
considered adulterated. Furthermore it is the plant management’s
responsibility to take precautions to ensure disease control,
cleanliness, education and training, and supervision in a food
processing and foodservice establishment.
Disease control can be achieved by implementing good
sanitation practices. It may be required that staff report to a
supervisor any change in health.
In case of an illness, that person may not work in direct
contact with food, or food contact surfaces, or food packaging.
Also a prospective employee should be examined by a health
professional to make certain that no obvious health problems
exist.
Cleanliness requires that an employee practice
good personal hygiene. Garments should be
clean and suitable for the operation. Hands
must be washed and sanitized before starting work and every time
they get soiled, especially when touching the nose or other body
parts. Washstands must be easily accessible, foot operated,
and supplied with soap and paper towels.
Loose jewelry should not be worn in food preparation, food
processing, or food packaging area. For the
same reason, no pens, pencils, marking pens, or other loose items
may be carried in the breast pocket. The use of gloves must
be decided on a case-by-case basis.
Hair and beard restraint should be used to prevent food
contamination. Personal clothing (coats, jackets) should be
kept in a room removed from the food preparation, and equipment or
utensil washing areas.
Similarly, eating, drinking, smoking, or chewing gum may
only be allowed in a designated area, again removed from the food
handling areas.
In order to assure food safety, GMP requires
that the grounds surrounding the processing plant or food service
establishment be well maintained. Grass should be mowed
regularly, and there should not be any standing water.
The yard, if blacktop, should be free of dirt and garbage,
which might harbor pests (insects and rodents) and allow
accumulation of microorganisms that could be carried by workers
into the plant. Garbage and waste disposal
bins may not be close to any doors leading to the food processing
plant or foodservice establishment. The bins must be tightly
closed to prevent access for pests and should be emptied
frequently.
The building must be well designed and
constructed. There may not be any cracks in
the walls or open spaces around the doors. The
doors should close automatically. Workspace
within the plant should be adequate for equipment, manufacturing
activities, and sanitary operations. The
floors, walls, and ceilings must be in good condition and easily
cleaned. Paint should not be used if there is a chance for
it to peel, because that will place additional stress on the
sanitation activity.
Adequate lighting must be provided in all areas to allow the
employees to perform their task well.
Ventilation must be effective to minimize odors and vapors
and avoid condensate accumulation, which may result in food
contamination. Positive pressure is
recommended wherever possible to minimize contamination of the
product by microorganisms from the raw materials receiving and
processing areas. Where appropriate, the windows and doors
should be screened.
The sanitary operations, facilities, and
controls require that the following aspect be addressed: (a)
general maintenance, (b) substances used in cleaning and
sanitizing and their storage, (c) pest control, (d) sanitizing of
food-contact surfaces, (e) water supply, (f) plumbing, (g) sewage
disposal, (h) toilet facilities, (i) hand washing, and (j) rubbish
and offal disposal. Thus cleaning and
sanitizing of equipment must be performed in a manner that will
prevent contamination of food, food-contact surfaces, and food
packaging materials. Standards for processing
equipment have been developed by the dairy industry and have been
designated as 3A Sanitary Standards. Although most
processing equipment is stainless steel, it is important to
remember that it is corrosion resistant and not corrosion proof.
Consequently, cleaning and sanitizing solutions that are
manufactured for that purpose are only effective when used in
recommended concentrations.
The first step in cleaning equipment is to
remove excess soil. Although hot water is preferred for
fatty foods, cold water is recommended for protein soils.
There are many cleaning products on the market.
A preferred cleaning agent should have a good surfactant
activity, which will reduce the adhesion of the soil to equipment
surfaces. Such compounds are referred to as
sequestrants, and while EDTA and associated compounds are good
sequestrants for organic soils, polyphosphates are good
sequestrants for inorganic soil. There are
products available that also contain sanitizing agents, which
improve cleaning. Although it would seem that
cleaning compounds that contain multiple functionality would save
on materials and labor, such cleaning agents may not be the best
product to use. In fact when processing
different products, it may be necessary to have more than one type
of cleaner. It is essential to make certain
that the intended cleaning agent is compatible with the type of
water in use, although some cleaning agents have built in water
softeners. Cleaning agents with an alkaline base are best for
preventing mineral scale buildup.
Chlorinated caustic and alkaline products enhance cleaning.
Acid cleaners are considered good in removing mineral scale
buildup. Depending on the equipment, scrubbing may or may not be
necessary.
Throughout cleaning it is essential to remove
any biofilm that may have formed. It is not
recognized that bacteria growing on food-contact surfaces will not
only adhere to the surfaces, but will also secrete proteinaceous
or polysaccharide material, forming a glycocalyx matrix.
Such cell aggregates are more resistant to removal during
cleaning, they are also more resistant to sanitizers and even to
heat. Cleaning is expected to remove 100% of the soil, and only
then should sanitizers be applied.
Bacteria cannot be seen and even though the surface may
look clean, it may not be free of food borne pathogens.
The most popular sanitizer is chlorine. Effectiveness of
this sanitizer depends on the source of chlorine, concentration,
temperature, pH, contact period, type of microorganisms, and
presence of organic material.
While inorganic chlorine compounds release chlorine
quickly, organic compounds release it slowly.
Chlorine solutions are easily prepared, and the available chlorine
concentration is readily determined. Chlorine
is very quick acting and is effective against a wide range of
microorganisms. However, it will combine with any organic material
with which it makes contact, thus becoming unavailable for the
bactericidal action intended.
It will also combine with iron and phenolic and nitrogenous
compounds. Therefore to assure that enough chlorine has been
added, it is essential to add enough to meet the chlorine demand,
and then whatever is added beyond the breakpoint will be present
as free available chlorine (free residual chlorine).
In-plant chlorination requires the use of
automated chlorination of water used throughout the processing
plant. This practice can improve odor control
and product quality, but it must be stressed that chlorination is
no substitution for good sanitary practices.
While the correct concentration of chlorine (10 to 50 ppm) has an
excellent effect, an excessive amount of chlorine (>1,000 ppm)
is undesirable, because it may have no effect on the bacteria, may
cause odor problems with the product, may cause staining, is
irritating to skin and lungs, and will cause corrosion problems.
Chlorine looses activity as pH rises with increased
concentration of hypochlorite and
at high temperatures the chlorine is driven out of the solution.
Iodophores are also effective sanitizers.
These compounds contain iodine as the active ingredient.
Iodophores are more stable than chlorine, have surfactant
capacity, are not corrosive, and are effective against most
microorganisms.
Quartenary ammonium compounds (QUATS) are also popular although
they are not as effective as chlorine compounds.
QUATS are effective when used in preparations with
sequestering agents. They are affective against the Gram positive
bacteria and less effective against the Gram negative group.
New and improved sanitizers and sanitizing agents have been
appearing in recent years with excellent results.
Before such compounds are used in the food processing
industry, itis essential they be acceptable by the appropriate
government agency.
All operations, starting with receiving and inspecting and
ending with packaging and storage or shipment, must be performed
in accordance with good sanitary practices.
To assure that raw material safety and quality standards
are acceptable, such standards can be part of the purchase
agreement and should be verified by the buyer.
This approach applies to all ingredients purchased from any supplier. The
importance of these factors becomes clear when it is realized that
the safety of the product becomes the responsibility of the
ultimate manufacturer, including foods that do not receive
bactericidal thermal process.
To assure product quality and safety, GMP
requires “careful monitoring of physical factors such as time,
temperature, humidity, aw, pH, pressure, flow rate, and
manufacturing operations such as freezing, dehydration, heat
processing, acidification, and refrigeration to ensure that
mechanical breakdown, time delays, temperature fluctuations, and
other factors did not contribute to the decomposition or
contamination of food. ” Furthermore, “food
that can support the rapid growth of undesirable microorganisms,
particularly those of public health significance, shall be held in
a manner that prevents the food from becoming adulterated”
(21CFR110). And finally, should processed food or ingredients
become contaminated, the product can either be reprocessed (if
applicable), or destroyed. Safety
of the final product is then based on the microbiological
analysis. Sampling of large lots becomes expensive, and the
likelihood of detecting a food pathogen becomes a statistical
probability that may or may not prove the safety of the lot
examined.
Despite adherence to the above or similar
regulations, each year there are a significant number of products
in the U. S. , Canada, England, and Australia involved in food borne
illness outbreaks. To minimize production
costs while increasing product safety, a new concept known as
Hazard Analysis Critical Control Point (HACCP) was introduced
several years ago and is now being implemented.
HACCP programs are now required for processors of seafood,
meat and poultry products and fruit and vegetable juices.
The
HACCP concept is based on seven basic components:
1. Hazard analysis is performed for the entire operation and
any potential hazard is identified.
2. Critical control points are identified, points that require
control of the hazard.
3. Monitoring parameters are specified that indicate whether
the system is in control.
4. Limits are established beyond which the system is out of
control.
5. Corrective action that must be taken to bring the system
back into control is specified.
6. Records must be kept and reviewed in order to make necessary
adjustments.
7. A verification procedure must be employed to assure that the
system is working.
When
developing a HACCP program, the first step is to prepare a flow
chart. A HACCP program for crabmeat could be
as follows:
Crab Processing Flow Chart
1. Live crab receiving
CP
2. Culling
CP
3. Cooking CCP
4. Removal from cooking
vat CP
5. Chilling CP
6. Dismemberment
7. Picking meat CCP
8. Packing CP
9. Refrigeration CCP
10.
Distribution CP
CP = control point
CCP = critical control point
There are three types of hazards that must be controlled: (1)
biological hazard, (2) chemical, and (3) physical.
Hazard analysis is in part based on observations and
statistical data regarding frequency of food borne illness
outbreaks as well as the potential for such outbreaks.
Foods that are ready to eat and are routinely not heat
processed before consumption bear the highest risk or hazard
(Category I). This category includes crabmeat, milk, eggs, oysters
on the half shell, and similar foods.
An additional reason for placing crabmeat in the high-risk
category is that crabs come from an environment where one can find
Listeria monocytogenes, Vibrio parahaemolyticus, and
Vibrio vulnificus.
·
Step 1 in the processing sequence is important control point (CP)
at which the processor must determine whether the shipment is
worth accepting for processing.
·
Step 2 is important since at this stage it is essential to remove
any dead crab that may be present in the shipment.
·
Step 3 is considered a CCP, because all pathogenic
bacteria must be killed at this point. Additional concerns
are that overcooking may result in lower yield, but undercooking,
while resulting in a poor quality product, carries the real danger
of allowing pathogens to survive.
·
Step 4 is the next CP that requires close attention, because as
the cooked crab is removed from the vat, all precautions must be
taken to prevent recontamination.
This aspect is more difficult to address than it may
appear, since in a plant one must take all precautions to prevent
traffic between raw and cooked product.
·
Step 5 The chilling of cooked crab is a control
point. Here again all precautions must be
taken to prevent the cooked product of becoming contaminated,
which will readily occur if contact, direct or indirect, between
raw and cooked product can not be assured.
While this processing step must be closely controlled, one cannot
designate it a CCP, because too many CCPs can cause the system to
break down.
·
Step 6 Dismemberment is frequently performed after the crabs have
been cooled to simplify further processing.
This step need not be critical, but a person who has no
contact with the raw crab receiving area must perform it.
Containers used for carrying crabs and crab parts between
Step 3 and Step 6 must be frequently cleaned and sanitized.
·
Step 7 Meat removal operation should be
considered a CCP, because extensive handling of picked meat occurs
at this step, as well as there is a delay between picking and
packaging. The possibility exists for
temperature change at this step, which could lead to growth of
pathogens if present. The picking operation
requires more workers than any other processing step, adding to
the possibility of contamination. Furthermore, there is no
subsequent step that could be used to remove or destroy any
pathogens that may have been introduced.
In fact, after boiling the raw crab there is no processing
step that can be used to remove or destroy any pathogens.
Proper clothing, hairnets, hand dips, preventing delays
between picking and packing, and all other precautions must be
strictly enforced.
·
Step 8 Packaging is a relatively short operation, but an eye
should be kept on preventing possible contamination and therefore
a CP, because once contaminated the product will reach the
consumer in that state.
·
Step 9Refrigeration of the product must be
maintained at < 400 F to prevent
bacterial growth and is thus a CCP. Temperature control must
be closely monitored, since that is the only procedure to assure
microbiological safety and quality.
·
Step 10Shipping is similar to that of Step 8, refrigeration
is essential at all times.
As part of the HACCP program, temperature
monitoring of the coolers, chilled crabs, crab parts, and picked
meat is important. Furthermore, turnover rate of the crab parts in
the picking room is very pertinent.
Verification could require environmental and product
sampling for total, viable bacterial count, fecal coliforms, and
Listeria monocytogenes at specified time intervals.
REFERENCES
Banwart, G. J. 1989. Basic Food
Microbiology, 2nd ed. , New York: Van Nostrand
Reinhold.
Doyle, M. P. ed. 1989. Foodborne Bacterial
Pathogens. New York:
Marcel Dekker.
Gould, W. A. 1990. cGMP’s/Food Plant Sanitation. Baltimore,
MD: CTI Publications.
Potter, N. N. 1986.
Food Science, 4th ed. Westport, CT: AVI Publishing.
Troller, J. A. 1993.
Sanitation in Food Processing, 2nd ed.
New York: Academic Press.
CODE OF FEDERAL REGULATIONS (CFR)
&
GOOD MANUFACTURING PRACTICES (GMP)
Code of
Federal Regulations and Good Manufacturing Practices can be seen
and/or printed from the web site:
http://www. access. gpo. gov/nara/cfr/cfr-table-search.html
From that
site select “Retrieve CFR section by citation”.
For
RECALL use TITLE 21 PART 7
SUBPART C (guidelines on policy, procedures, and
industry responsibilities).
http://www. cfsan. fda. gov/~lrd/recall2.html
For
GMP use TITLE 21 PART 110
SUBPART A (general provisions), B
(building and facilities, C (equipment), E
(production and process controls), and G (defect
action level).
http://www. cfsan. fda. gov/~lrd/part110t.html
For
ACIDIFIED FOODS use TITLE 21 PART 114
SUBPART A (general provisions), E
(production and process controls), and F (records
and reports).
http://www. cfsan. fda. gov/~comm/lacf-toc.html
Posted 05/2005
Site posted and
maintained by
Katherine
Davis-Dentici
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