Bacterial quality of three casserole dishes served in a university food service
by Mary Eleanor Ginther
A thesis submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE in Home Economics
Montana State University
© Copyright by Mary Eleanor Ginther (1972)
Abstract:
Bacteria may be transmitted through foods and cause discomforting gastrointestinal, illnesses in
unsuspecting persons who ingest such contaminated foods. Particulary prevalent pathogens of concern
to manufacturers, processors, and consumers of food are the organisms - Staphylococcus aureus,
Salmonella, and Clostridium perfririgens. The ability of these bacteria to survive -and proliferate in
foods depends on several factors such as pH, water activity, mechanical forces, ingredients,
competitive saprophytic organisms and temperature. The latter factor is probably a major one in large
quantity cookery but total bacterial response will determine if the food will exhibit an antagonistic or
beneficial effect on the exogenous organisms.
The current study was done to evaluate three casseroles bacteriologically which were processed and
served from one dormitory cafeteria on the campus of Montana State University. The food services had
recently initiated an expanded program of serving which necessitates foods to be maintained at
warming temperatures for longer periods, which could be hazardous if not carefully controlled. The
methods used in this study are those commonly used and accepted by authorities in food microbiology.
The results show that the foods tested were of. high bacteriological quality. STATEMENT OF PERMISSION TO COPY
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fulfillment of the requirements for an advanced degree at
Montana State University, I agree that the Library shall
make it freely available for inspection.
I further agree
that permission for extensive copying of this professional
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professor, or, in his absence, by the Director of Libraries.
It is understood that any copying or publication of this
professional paper for financial gain shall not be allowed
without my written permission.
BACTERIAL QUALITY OF THREE CASSEROLE DISHES
SERVED IN A UNIVERSITY FOOD SERVICE
by
MARY ELEANOR GINTHER
A thesis submitted to the Graduate Faculty in partial
fulfillment of the requirements for the degree
of
MASTER OF SCIENCE
in
Home Economics
Approved:
Head, Major Department
_
— JLaj _' c X ■
—
J/Cji-,.
Chairman, Examining Cd^nmitt/e
Graduate i?Dean
MONTANA STATE UNIVERSITY
Bozeman, Montana
August, 1972
iii
ACKNOWLEDGEMENTS
I would like to express due appreciation to those
persons who directly supervised me in this task as well as
to parents, sister and numerous friends who lent support
as well .as challenge to me in .graduate school.
My thanks and gratitude to:
Dr. Andrea Pagenkopf who donated constant effort and
much extra time as well as much patience and guidance as a
friend and advisor.
Mr. Glen Lewis, as well as other supervisors and
employees of the Campus Food Service, whose cooperation made
this study possible.
The members of my committee who were very helpful and
cooperative in their efforts. This includes Dr. John Jutila,
Dr. Robert Lind, Dr. Robert Dynes, and previously Dr. James
Boyd.
A 'very special thanks to my parents, my sister Sonja,
and Mrs. Karen Olsen who aided me in numerous tangible and
intangible ways, and who were so consistent in this help
throughout my entire program of study.
TABLE OF CONTENTS
Page
LIST OF TABLES.............. .. . .............
ABSTRACT. . . ..................
. . . . . . . . . .
Chapter
I.
TI.
INTRODUCTION. . . . . ............
I
REVIEW OF LITERATURE. . .....................
6
Introduction..............
6
Statistics of Foodborne Illnesses
......
6
Characteristics of Food Poisoning
Microorganisms . . . . . . . . . . . . . .
11
Salmonellae ......................
11
Staphylococci............................. 12
Clostridium perfringens.
.............
14
Factors Affecting the Growth of
Microorganisms in Foods. . .. ...........
15
T e m p e r a t u r e ...................... .. .
Heating..................
. . . . .
Cooling.
^
.
Holding..............................
15
15
23
25
Ingredients in a Recovery Medium . . . .
Competition of Microorganisms..........
26
32
Quality of the Finished Product
. . . . . .
Preparation as a Factor in Food
Contamination.................... .. .
Etiology of Some Specific Outbreaks
Summary
....
. . . . . . . . . . . . . . . . . . .
35
36
40
42
V
Chapter
III.
Page
METHODS.............
45
Preparation of Casseroles ................
46
Collection of S a m p l e .................. .. -
47
Preparation of Hoinogenate . . . . . . . . .
49
Aerobic Mesophilic Plate Count. . . . . . .
50
.Coliforms . . . . . . .
Staphylococcus. . . .
..................
........
51
. . . . . .
53
S a l m o n e l l a ..............
55
Clostridium perfringens .......
. . . . .
59
Treatment of D a t a ......................
60
IV.
RESULTS AND DISCUSSION..................
61
V.
SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS.
Summary . . . . . . . . . . . . .
........
Conclusions ..........
Recommendations . . . . . . .
.
73
73
75
............
76
LITERATURE CITED ..........................
78
A P P E N D I X ..............
96
LIST OF TABLES
Table
I.
2.
3.
4.
Page
The Number and Percent of Cases and Outbreaks
of Foodborne Illnesses Acquired in Schools
and Restaurants, United States, 1969-70. . . . .
8
Foodborne Outbreaks of Bacterial Origin and
the Percentage Caused by Staphylococcus
aureus, Salmonella, and Clostridium
"
perfringens, United States, 1969-1970 . . . . .
9
Three Most Frequent Vehicles Associated with
Foodborne Illnesses Caused by Each of the
Organisms, Staphylococcus aureus, Salmonella,
Clostridum perfringens in the United
States, 1969-1970. . .......................
10
Comparison of Plate. Count Averages of Four
Sampling Times of Three Casserole-Type
Dishes Served in One College Cafeteria . . . . .
62
vii
ABSTRACT
Bacteria may be transmitted through foods and cause
discomforting gastrointestinal, illnesses in unsuspecting
persons who ingest such contaminated foods. .Earticulary
prevalent pathogens of concern to manufacturers, processors,
and consumers of food are the organisms - Staphylococcus
aureus, Salmonella, and Clostridium perfririgens. The
ability of these bacteria to survive and proliferate in foods
depends on several factors.such as pH, water activity,
mechanical forces, ingredients, competitive saprophytic
organisms and temperature. The latter factor is probably
a major one in large quantity cookery but total bacterial
response will determine if the food will exhibit an anta­
gonistic or beneficial effect on the exogenous organisms.
The current study was done to evaluate three casse­
roles bacteriologically which were processed and served
from one dormitory cafeteria on the campus of Montana State
University. The food services had recently initiated an
expanded program of serving which necessitates foods to be
maintained at warming temperatures for longer periods,
which could be hazardous if not carefully controlled. The
methods used in this study are those commonly used and
accepted by authorities in food microbiology. The results
show that the foods tested were of. high bacteriological
quality.
CHAPTER I
INTRODUCTION
Certain microorganisms and parasites are transmitted
through foods and may cause illness to persons who IngeSt
these foods.
For some microorganisms food is merely a
vehicle of transmission.
growth.
For others it is a good medium of
Outbreaks of acute intestinal enteritis caused by
the ingestion of a food in which pathogens have multiplied
are referred to as food poisoning outbreaks.
Microorgan­
isms which may cause foodborne illness include bacteria,
viruses, rickettsiae, and protozoa.
Bacteria are the organ
isms which most commonly cause gastrointestinal illness.
Common symptoms are intestinal upset, vomiting, diarrhea,
nausea, and malaise (I).
Each year thousands of cases of food poisoning are
reported in the United States.
from state to state.
These reports vary widely
There is reason to believe that the
number of foodborne illnesses is much higher than the
reported statistics show.
Reporting is not compulsory in
any state, and it is false to assume that the states with
the greatest number of cases have the poorest sanitary
conditions. Very often small outbreaks, say in a family,
go unreported while the more dramatic outbreaks involving
2
hundreds of people receive undue attention.
Contrastingly,
large outbreaks may receive no attention at all due to an
organization's fear of publicity.
Needless outbreaks
continue with the accompanying economic losses and the mani­
fold problems of resulting illnesses.
Proper surveying of
outbreaks could increase the knowledge of foodborne
diseases.
Reliable information is needed in order to pro­
tect the consumer.
Occurrences of foodborne illnesses have been
reported from many types of food service establishments—
restaurants, hospitals, and schools, for example.
Paramount
to an effectual sanitary control of menu items is an under­
standing of the reservoirs of the potentially dangerous
organisms, conditions favoring food contamination in food
preparation,_.areas, and the conditions allowing profuse
growth of bacteria in foods. . Some foods are much more likely
to be indicted in occurrence of foodborne illness due to the
nature of their ingredients and the handling procedures they
receive.
The food handlers practice effective sanitary
\
habits, use fresh and unadulterated ingredients, and allow
foods to undergo adequate heating or cooling.
Prepared
foods, such as casseroles or sandwich spreads, are thus a
good indication of the adequacy of all the foregoing factors.
3
Keeping the above points in mind, a study was under­
taken to evaluate the bacteriological quality of certain
prepared foods in a college cafeteria.
Casseroles were
chosen because they represent a major menu entree which is
frequently offered.
Also, such dishes are a potpourri of
ingredients— fresh foods, and leftovers, such bacteriologically susceptible items as milk and eggs, and also some
less vulnerable items like noodles.
tain major ingredients such as:
These casseroles con­
beef, pork, poultry, or
fish— which is surrounded by a starchy base.
The total
result is a protein and carbohydrate mass which is readily
susceptible to bacterial contamination (2).
Cooking pro­
cedures should render such dishes safe from harmful patho­
gens.
There is an additional danger in cafeterias or other
public eating places where food must be maintained at
temperatures hot enough to stop bacterial proliferation,
while not so hot that the aesthetic appeal of the food is
destroyed.
The task of the food service is to take raw
ingredients and formulate them into a safe and attractive
food dish.
The final goal is to heat the food enough to
eliminate pathogens and maintain it at temperatures which
keep the food continually safe for the consumer.
4
The present study was undertaken for three major
reasons, which are as follows:
the large percent of out­
breaks occurring in schools, the current extended serving
hours now used in many cafeterias, and the lack of data in
this area.
Recently, many college cafeterias have been
experimenting with using an increased number of hours dur­
ing which food is served during the day, in order to accom­
modate students more amply.
It is not improbable to think
that such extended.serving hours might increase the sus­
ceptibility of food to bacterial contamination.
In 1968,
1969, and 1970, the incidences of food poisoning in various
public food establishemts was 44%, 30%, and 32% respectively
of all places where such illnesses occurred.
In 1969, 70%
of these occurrences were in schools (3, 4).
These factors
lend some probability to the premise that such dormitory
food could be a good reservoir for pathogens since these
foods are kept at holding temperatures for such long periods
of time.
The information inherent in such a study would be
of interest to food service managers. . It would allow them
- ' - Xi
to know more accurately the bacteriological quality of the
food served to the customers.
5
Hypotheses
1.
Is there any evidence of Clostridium perfrIngens7
Salmonella, or Staphylococcus aureus in the casseroles
examined bacteriologically in this cafeteria?
2.
If there is evidence of contamination, would
proper heat treatment have eliminated the danger?
3.
Are increased sanitation procedures needed to
insure a greater amount of consumer safety?
reliable suggestions can be mad9?
4.
If so, what
>
Do the lengthened serving hours have implications
as far as food safety in this cafeteria is concerned?
CHAPTER II
REVIEW OF LITERATURE
Introduction
Disease or illnesses, a state wherein people operate
at a less than optimal level, is a definite concern to those
interested in public health.
is bacterial illness.
One of these suboptimal states
In particular, this paper will deal
with sicknesses developing from the consumption of various
contaminated foodstuffs.
Several species of bacteria are
exogenous contaminants of food.
Some foods are conducive
to the proliferation of bacterial contaminants, making these
foods good vehicles for foodborne illnesses.
The organisms
which engender these illnesses in humans via foods are called
food poisoning organisms.
The resulting maladies are char­
acterized generally by a short incubation period after the
consumption of the dangerous food.
Gastrointestinal upsets
are the earliest symptoms accompanied later by less local­
ized manifestations.
The most frequently reported causes of
food poisoning are members of the Salmonella species.
Staphylococcus aureus (Staph, aureus), and Clostridium
perfringens (C. perfringens) (3, 4).
Statistics of Foodborne Illnesses
Statistics from previous years as reported in Food­
borne Outbreaks (3, 4) yearly summaries show that public
7
food service establishments are the most common places of
acquisition of foodborne disease.
This includes restaurants,
delicatessens, cafeterias and schools.
Schools were respon­
sible for 70 percent of all reported cases in 1969 and 21
percent of all persons acquiring illnesses in all places in
1970.
(See Table I on page 8.)
of Staph, aureus.
Evidence of the importance
Salmonella, and C. perfringens as factors
in the incidence of foodborne diseases is given in Table 2,
page 9.
These three organisms together were responsible for
56 percent of all bacterial caused foodborne outbreaks in
1969 and 1970 (3, 4).
Staphylococci account for the largest
percentage of outbreaks from one bacterial species.
Beef
accounted for 16 percent of all vehicles in 1969, pork 10
percent turkey 8 percent.
The respective figures for
1970 were 18 percent, 16 percent, and 11 percent for a total
<
of 45 percent in 1970 and 34 percent in 1969 of all foods
which harbored food poisoning organisms.
Table 3, page 10,
shows the three most prominent foods responsible for
illnesses
caused by the three types of organisms.
Data
available shows a higher incidence of foodborne disease in
the warmer months from April to October (3,4).
for all months is not great.
The variation
Table I
THE NUMBER AND PERCENT OF CASES AND OUTBREAKS OF FOODBORNE
ILLNESSES ACQUIRED IN SCHOOLS AND RESTAURANTS,
UNITED STATES, 1969-70a
Cafeteria
Restaurants
Number of persons ill
1969
Schools
1970
Cafeteria
Schools
Restaurants
3,904 (14%) 19,842 (70%)
9, 580 (31%)
27
(25%)
5
(13%)
33
(26%)
8
(30%)
7
( 6%)
3
( 8%)
18
(15%)
3
(12%)
33
(30%)
17
(45%)
27
(20%)
7
(28%)
Total caused by
above
67
(61%)
25
. (66%)
78
(61%)
18
(70%)
Other causes
43
. (39%)
38
(34%)
51
(39%)
8
(30%)
HO
(100%)
63
(100%)
129 (100%)
26
(100%)
4913
(21%)
Percentage Outbreaks
caused by:
Staph, aureus
Salmonella
C. perfringens
Total
aUnited States Department of Health, Education and Welfare
Foodborne Outbreaks Annual Summary. Atlanta, Georgia: Center for Disease
Control. Page 16. 1969-1970.
9
Table 2
FOODBORNE OUTBREAKS OF BACTERIAL ORIGIN AND THE PERCENTAGE
CAUSED BY STAPHYLOCOCCUS AUREUS. SALMONELLA.
AND CLOSTRIDIUM PERFRINGENS.
UNITED STATES, 1969-1970a
% of total
1969
Foodborne outbreaks of
bacterial origin
% of total
1970
66
66
Staph, aureus
25
28
Salmonella
13
13
C . perfringens
18
15
56
56
Percent of Bacterial Foodborne
Outbreaks Caused by:
Total of outbreaks caused
by three organisms
aUnited States Department of Health, Education,
and Welfare. Foodborne Outbreaks Annual Summary. Atlanta,
Georgia: Center for Disease Control, page 3, 1969-1970.
10
Table 3
THREE MOST FREQUENT VEHICLES ASSOCIATED WITH FOODBORNE
ILLNESSES CAUSED BY EACH OF THE ORGANISMS,
STAPHYLOCOCCUS AUREUS, SALMONELLA,
CLOSTRIDIUM PERFRINGENS IN THE
UNITED STATES, 1969-1970a
Foods Incriminated
by:
% of Total
1969
% of Total
1970
Staph, aureus
Pork
Beef
Turkey
30%
15%
11%
Pork
20%
Unknown 15%
Bakery
Products L
Salmonella
Turkey 20%
Unknown 20%
Chicken 13%
Unknown 20%
Turkey 17%
13%
Beef
Beef
47%
Turkey 22%
Vegetablesif
6%
Fruit
42%
Beef
Turkey 24%
Unknown 9%
C .perfringens
aUnited States Department of Health, Education,
and Welfare. Foodborne Outbreaks Annual Summary, Atlanta,
Georgia: Center for Disease Control, page 14, 1969-70.
These statistics give some indication of the preva­
lence of these types of bacterial food illnesses and thus
the importance of preventive measures in food service
establishments.
This information is indicative of all
reported incidences, but it should not be assumed that it
is complete for all occurring cases.
11
Characteristics of Food Poisoning
Microorganisms
Foodborne illnesses are of two types:
intoxications.
Infections and
An infection occurs when a large number of
live organisms are ingested.
An intoxication, however, is
the result of the ingestion of a toxin produced by an organ­
ism.
Live cells need not be present or be ingested .in .
order for an intoxication to ensue.
The distinction between
these two types is of significance in determining the heat­
ing procedure needed for making a product safe for consump­
tion (I).
Salmonellae
Salmonellae are small gram negative rods, which grow
very well either aerobically or anaerobically.
grow optimally at room temperature.
The organisms
Nutritionally its
requirements are not fastidious— demanding neither vitamins
nor amino acids.
An outstanding trait of this group is its
inability to ferment lactose (5).
The illness, salmonel­
losis, caused by any of the genus of Salmonella, is an infec­
tion caused by the ingestion of the bacteria themselves.
It
is usually characterized by a 6-18 hour incubation period,
followed by gastrointestinal symptoms such as diarrhea, and
perhaps vomiting.
An elevated temperature is not uncommon.
12
Recovery is rapid, usually only a few days (6).
The organ­
isms are easily destroyed.by temperatures high enough to
pasteurize milk (79 C . for 25 seconds)
(I).
Staphylococci
Staphylococcal food poisoning, which is often said
to be the most common type (7), is caused by the ingestion
of a toxin which may be produced by proliferating cells of
Staph, aureus.
The organism is a gram positive coccus
commonly found in grape-like clusters.
One notable charac­
teristic is the ability of the organisms to ferment mannitol.
Amino acids and several vitamins are essential to the growth
of Staph, aureus (5).
Millions of microorganisms must be
present for adequate toxin to be produced to cause disease.
Nausea, vomiting, diarrhea, malaise, and weakness occur in
the ailment, the onset of which is shortly after eating—
thirty minutes to three hours (6)..
The prime forces in staphylococcal food poisonings
are the enterotoxins.
There are five types— A, B , C, D ,
and E-— and of these, types, A is implicated in most cases
of illness.
Several reasons have been given for this
higher incidence.
One is that type A is a primary meta­
bolite while type B is produced secondarily.
seem to be more susceptible to enterotoxin A.
Also, humans
And since
13
pH 6-7 is preferred for production of type A, prepared
dishes are a good medium since their pH is usually within
this range (8).
The only reliable method of determining if
a food has caused staphylococcal food illness is to isolate
the toxin.
The presence of coagulase positive staphylococci
per se is not indicative of the illness as shown by the
existence of enterotoxin-forming coagulase negative staphy­
lococci as well as coagulase positive staphylococci which
produced no enterotoxin and so were safe for consumption (9).
The "presence of rapid growth and high numbers of a poten­
tially enterotoxigenic strains of Staph, aureus, though
undesirable, would not necessarily indicate the presence of
enterotoxin"
(10).
Most experts agree that staphylococci
must be present in high numbers (10®-10^ cells per gram of
menstrum) before a more than negligible amount of toxin
can accrue.
In raw and pasteurized milk, a 5 x IO^ cell
concentration per milliliter was necessary before enter­
otoxin A was produced (11).
The toxin is very stable to
high temperatures which will not inactivate it (2).
This
thermostability is partially due to a binding of entero­
toxin to various proteins such as myosin and metmyoglobin in
meat (12).
The production of enterotoxin is influenced by
the prevailing natural food flora (13) , by aeration (14).,
14
and by pH.
The production of enterotoxin A is highly
sensitive to acidity and so is very unlikely to be produced
in acidic foods (15).
Clostridium perfringens
C. perfringens causes a mild malaise, accompanied by
abdominal pain and diarrhea with an onset of illness 8-18
hours after the ingestion of contaminated food.
The. factors
responsible for inducing disease are not yet clearly under­
stood.
But it is known that populations of one million
organisms per gram of food are required before disease
results (6). . The bacterium is a plump, nonmotile gram posi­
tive rod occurring singly or in chains.
Capsules are usually
present and will develop in the absence of essential cellular
nutrients.
Vegetative cells are strictly anaerobic and
nutritive requirements are complex with nineteen amino
acids and numerous vitamins, and minerals essential for
growth.
Distinct toxins are formed each having preferential
conditions of incubation, medium, and pH.
The alpha-toxin
is the one .commonly associated with the virulence of this
organism (5).
The spores of C. perfringens were found to withstand
internal terminal temperatures of 74 to 77 C . (2).
Spore
formation occurs when vegetative cells are in an environment
15
lacking nutrients or other necessary constituents.
Authori­
ties usually recognize two types of C. perfringens— the heat
resistant and the heat sensitive.
The former is more common
in England while the latter is more prevalent in the United
States.
Heat resistant types will survive temperatures of
100 C. for sixty minutes and do not form spores as readily
as the heat sensitive types (16).
Factors Affecting the Growth of Microorganisms in Foods
Temperature
Heating
The major safety control mechanism used in large
quantity cookery is cooking proceeded by adequate cooling
of foods (2).
There, is still much unknown about the total
effect of heat on bacterial cells.
Sublethal heat can pro­
duce a variety of reparable lesions in a cell (17, 18, 19).
The amount of cells which will be destroyed by heating is
dependent on numerous factors including the degree and type
of heat, and the status of the organisms.
The type of heat
has an effect on the destructability of microorganisms.
Knowledge of the damage by moist heat in nonsporeforming
microorganisms remains incomplete.
At equivalent tempera­
tures, moist heat is usually more lethal than dry heat to a
1.6
bacterial cell— damaging the essential protein complexes.
Salmonellae are highly sensitive to moist heat, and their
resistance to heat increases steadily when moisture is
reduced (20, 21, 22).
Baldwin et al. found that S . typhi
and Staph, aureus were destroyed more completely when
cooked four minutes electronically than when cooked 30-40
minutes in a conventional oven (23).
Walker et al. reported
that older cultures of Staph, aureus required three times
longer heating for destruction than twelve hour cultures
(24).
Thermal time considerations are complicated by the
fact that some bacteria are more or less resistant to high
temperatures than others.
Read et al. found that the D
value (time required to kill 90% of bacteria) at 68.3 C . for
S. senftenberg 775W (heat resistant strain) was 10 seconds
while .28-.52 seconds were required for 90% kill of the other
six strains tested in whole milk (25).
Although most salmon-
el Iae strains are quite heat sensitive, it has been recom­
mended that S . senftenberg 775W be used as a reference strain
because heat treatment adequate to destroy it will likely
destroy all other salmonellae and staphylococci present
(26, 27).
Killing temperatures are also dependent on the
initial bacterial load as was shown by Read and his co­
workers with concentrations of S. senftenberg 775W, in which
17
pasteurization temperatures were satisfactory unless numbers
greater than 3 x IOj-* organisms per milliliter were present
(25).
Thomas et al. studied Staph, aureus and S. senften-
berg 775W, in four media and showed the need for establish­
ing probable numbers in a type of food before deciding a
valid heating time.
Large solid particles in a food will
alter heating times (26).
Some researchers have suggested
an internal temperature of 74 C . for eleven minutes to kill
salmonellae, allowing some margin of safety (28).
Effect of Heat on Enterotoxin. Production _
and Destruction
The presence of staphylococci in a food is not proof
that enterotoxin is also present.
Toxin production depends
on several factors including temperature.
Donnelly et al.
in one study found that enterotoxin was readily produced at
35 Co
The organisms were less able to produce toxin at
30 Co, 25 C., or 20 C .
No toxin was produced at 10 C . in
either raw or pasteurized milk (13).
In barbecued chicken
enterotoxin was produced at 35 C. but not at 40 C., 42,C.,
or 45 C . (29).
There is usually a delay in enterotoxin
production after Staph, aureus has been in the lag phase,
but this will resume as soon as favorable conditions are
restored (30).
18
The toxin production of C. perfringens is poorly
understood.
food.
There is no certainty that it is formed in
Rather, it may be produced when vegetative cells
multiply and grow in the intestine of a susceptible host
(31).
The toxin was found more stable and active for
longer times at 100 C . than at 75 C. (32).
Destruction of toxins is another effect of elevated
temperatures.
Denny et al. demonstrated that the greater
the toxin concentration the more heat is needed to inacti­
vate it (33).
Pure preparations of staphylotoxin were
lacking in thermostability compared to crude preparations.
At 121 C. the crude toxin required 1.7 times longer heating
times than did pure toxin for inactivation.
This is due in
part to the protection provided by proteins in a menstrum
(12, 34).
Toxins have been found to be more stable for
longer times at 100 C. in saline than in ground beef slurry.
It was more quickly destroyed at 80 C. in ground beef than
at 100 or H O C. (12, 32) .
Effect of Heat on Spores
Food processors should be aware of the relation of
heat to spore destruction and germination.
The heat needed
is dependent on many factors including the food medium.
beef, spores numbering IO^ per gram survived steaming for
In
19
five hours although there was a sevenfold decrease each
hour as reported by Barnes and his coworkers.(35),
Spore
formation was maximum at pH 6 at 30 C . in a medium void of
oxygen.
Ahmed and Walker found that a prerequisite condi­
tion was a twenty minute period of heat activation at 75 C .
(36).
Vegetative cells were killed at 74 C., but increased
temperatures activated spores (37) .
Several studies with
beef showed that only 3 percent of C. perfringens spores at
any temperature germinated without heat shock, thus causing
raw meat to be a poor sporulation medium (35, 38).
Recovery of
Microorganisms after Heat Treatment
The recovery of organisms which have experienced a
damaging period of heating is an important aspect of food
safety.
Recovery is affected by the physiological state of
the bacterium, the heating medium, and the recovery medium
(39).
It is generally agreed by researchers that there is
an extended lag phase following sublethal heating (30., 39,
40).
Jackson and Woodbrine stated that the generation time
after the lag phase may remain the same as for unheated
cells (30).
Staph, aureus heating in 10 percent NaCl solu­
tion showed a lag time two or three times greater than
unheated cells and a reduced range of temperatures in which
it could repair (19).
Growth was immediate on a good medium.
20
but was somewhat slower for heated cells than for similar
unheated cells (41).
The temperature of the recovery medium plays a role
in the cell's ability to resume normal growth.
Staph.
aureus exhibited a smaller temperature growth range during
revival (19).
In one study Nelson showed the maximum
temperatures for repair for gram positive organisms to be
32 C . at pH of 7, while a pH of 6 was more conducive to
the growth of gram negative organisms (42).
Salmonellae
recovered rapidly at 30 to 37 C., and somewhat slower
recovery occurred at 10 and 20 C .
No significant growth
occurred after five days at 5 C. (43).
Cooking Temperatures
Maintenance of good bacteriological quality in a
finished product depends on the handling practices and
proper heating of the final product.
Those products not
demanding testing for edibility must be properly treated.
The food service establishment bears responsibility for tak­
ing nonsterile ingredients and combining them into an aesthetic and safe food product.
Considering the large number
of food poisoning outbreaks for which food establishments
are responsible, it seems surprising that more studies have
not been done on product safety and the factors that affect it
21
(44).
Many foods depend on a period of effective heating
to make them safe for the consumer to eat.
No multiplication should occur in any part of a food
held at cooking temperatures.
The temperature required to
prevent multiplication will depend on the food and the
organism.
Due to certain protective or antagonistic ingred­
ient effects and other factors, a "safe" temperature for all
foods cannot be stated.
Likewise, temperatures which will
kill vegetative cells do not necessarily kill spores or
inactivate toxins.
Temperatures at or near boiling should
kill salmonellae, Staph, aureus, faecal streptococci and the
vegetative cells of C. perfringens (2).
Various studies have elucidated the processing
temperatures adequate for making certain dishes bacteriologically safe while still maintaining the aesthetic quality.
Angelotti and Foster found oven temperatures of 218 C.
prevented the growth of salmonellae and staphylococci in
custard, ham salad, and chicken a la king (45).
All S. typh-
imurium were destroyed in chicken casserole held at room
temperatures for four hours before cooking and then cooked
at 177 C. for 40 minutes in a study by Wiedman et al. (46).
C. perfringens survived temperatures of 94 C. in stuffed
turkeys causing a hazard at subsequent storage temperatures
22
which permitted multiplication (47).
Hall and Angelotti
found vegetative cells of C. perfringens Were completelyinhibited at 49 to 52 C . in meats although rapid growth
occurred at 45 C . (48).
Barbecued chicken had to be main­
tained at internal temperatures above 60 C. to destroy
vegetative cells of C . perfringens (29).
A study by Gund­
erson and Kereluk on the survival of Staph, aureus,
Escherichia coli (E. coli), Streptococcus faecalis (S.
faecalis), and Bacillus cereus (B. cereus) in meat pies
showed survival to be a.mere .0001-.I percent after 40
minutes at an oven temperature of 217 C .
Counts for all
organisms continued dropping during a 10 to 20 minute wait­
ing period after baking except for Staph, aureus, which
demonstrated no change at all after removal from the oven
(49).
The bacteria in turkey and beef held at 68 C . during
cooking were viable for six hours with no marked change in
stability (50).
Heating turkey and dressing to 74 C .
internally was found inadequate to kill C. perfringens
spores.
If not served or chilled immediately the turkey and
dressing were potentially dangerous (37).
In studies with
Staph, aureus and S . senftenberg 775W (the former is heat
sensitive) with custard, ham salad and chicken a la king
Angelotti etal. indicated that heating perishable foods of
23
that type, to 66 C. internally and holding every particle of
food at this temperature for at least twelve minutes will
reduce ten million or less salmonellae or staphylococci per
gram to nondetectable levels.
for 78-83 minutes (45).
Equally effective was 60 C.
Bayne et al. agreed that 66 C . is
a high enough temperature to kill an innoculum of 2.5 x 10®
organisms per gram of S. typhimurium and S. senftenberg 775W
in chicken a la king and ground chicken meat (51).
Various
factors determine the effect of heat on survival of bacteria
in foods (52).
Cooling Temperatures
The cooking zone is described as the temperature rang=
which should be high enough to destroy vegetative cells in
a relatively short time.
Warming temperatures should utilize
temperatures high enough to prevent multiplication although
usually not killing microorganisms.
The danger zone is
that range from. 7 to 60 C . in which multiplication of
organisms is the greatest.
The chilling zone should permit
temperatures low enough to prevent multiplication over an
extended storage period (2).
The Public Health Department
is aware of this in stating its regulations.
Processed foods
are safe above 60 C . and below 7 C . with hazards predictable
between these temperatures (52).
Such things as overcrowded
24
refrigerators, poor cooling systems, or food aliquots too
large to allow even cooling tend to make cooling a dangerous
process.
The properties of a food affect the minimum tempera­
ture at which it will support bacterial growth.
Most food
poisoning organisms grow in a narrow pH range when at low
temperatures (54).
The common food poisoning organisms
will not proliferate below freezing.
Viable organisms
decline rapidly at temperatures just below freezing (-2 C.).
The decline is less rapid at temperatures lower than this
(55).
Plate counts done on turkey and beef held at 5 to
10 C . indicated stabilization or decrease (50).
Tempera­
tures below 6 C . are needed to prevent the growth of staphy­
lococci and salmonellae in foods.
Storage longer than one
day will result in a very slow increase, unless the food is
grossly contaminated.
This proved true in custard, chicken
a la king, and ham salad.
custard.
Multiplication was slowest in
Toxigenic staphylococci will multiply at a temper­
ature of 8 C. (56).
Staph, aureus showed little growth in
cooked ham at 4 C. (57).
Lewis et al. found that a 100-
serving quantity of chicken salad showed little bacterial
increase after 72 hours at 10 C.
(58).
C. perfririgens
demonstrated no growth in the range of 5 to 15 C . even after
25
five days' storage (48).
The spores of C. perfringens
survived six months at -5 C. and -20
Ci
There was little
change in spore counts at temperatures of I C., 5 C., 10 C.
or 15 C.
Vegetative cells were slowly destroyed at these
temperatures (35).
Another researcher found a reduction of
two or more logs in viable vegetative cells of C . perfrln- ■
gens at refrigeration or freezing temperatures (59).
Of the
three organisms of concern here, salmonellae are the most
sensitive to freezing (55).
Foods held below 5 C. will not
support growth of this bacterium.
Growth of salmonellae in
processed foods was prevented, below 5.5 C .
Storage of pro­
cessed foods at 10 C. will not eliminate the multiplication
of dangerous organisms (54).
Holding Temperatures
It is difficult to state how many hours a food can be
kept safely in the 7 to 60 C. range.
factors which influence holding time.
There are several
It is presently agreed
that the time should not exceed four hours, but that two
hours would lend a better margin of safety (2, 60).
Salmonellae and staphylococci did not multiply in custard
held at internal temperatures of 47 to 49 C . but decreased
in numbers.
In chicken a la king, staphylococci grew at
44 C . but were killed at 47 C.
The results of this study
26
indicate that the range of 6.5 to 46 C. is the danger zone
for bacteria growing in processed foods (60).
Chicken
salad that was held at room temperature (25 C .) for 24 hours
exhibited a rapid bacterial increase (58).
At 40 C ., !5.
typhimurium grew, as did C. perfringens, in barbecued chic­
ken (29).
Salmonellae and staphylococci grew well in
chicken a la king at 35 C.
The counts decreased 60 to 90
percent in 12 to 24 hours as temperatures rose to 45 C. and
49 C. (60).
Casseroles held at 20 C . to 35 C . for four
hours were not harmful, but periods to eight hours were not
recommended (46).
Total plate counts from beef and turkey
increased rapidly at 24 C. in six hours. At 37 C . cells
increased rapidly in four hours (50).
Rapid growth of
C. perfringens cells occured at 45 C . in meat and meat
dishes.
Researchers advocate caution in foods cooked and
held at 43 to 46 C. because C. perfringens heat resistant
spores are likely to germinate (48).
Ingredients in a Recovery Medium
The type of ingredients in a food menstrum has a
marked effect on the ability of cells to recover and survive
after heating processes.
Bacterial cells have more exacting
nutrient demands following heat damage, as do spores, and
are possibly more sensitive to antagonistic ingredients
27
(61, 62).
The ingredients— as part of the total environ­
ment— help determine if a particular organism
or group of
organisms can withstand heat treatment in a given food.
While an ingredient may exert a markedly lethal effect on a
microorganism in one situation, it may be enhancing in
another.
Thus, ingredient effect is not a static phenomenon
Very closely related to this is the available water
(Aw) in a food.
Aw is a property governed largely by the
commodities (solutes) in the food which bind a.certain
amount of water in that food.
Ingredients, in this, way,
also exhibit a protective or antagonistic role towards ■
.
microorganisms.
One study of Calhoun, and Frazier revealed
that the diffusion of solutes into gram positive cells was
more rapid than into gram negative cells with their higher
lipid content.
Thusly, Staph, aureus was killed more
promptly than E . coli regardless of "the solute used (63).
It is impossible to draw any conclusions concerning the
effect of Aw because present research does not indicate that
it is the sole reason for the effect of ingredients on
bacteria.
Rather, there is probably some overall ingred­
ient effect (64).
Aw has influence on spore production for
it seems that C. perfringens requires a-higher Aw for spore
production than for vegetative growth (65).
The production
28
of enterotoxin is also influenced by Aw.
When the initial
number of staphylococcal cells was greater than 10^-10^
cells per gram,.no enterotoxin was produced if the Aw was
less than .96.
This is partly due to the marked effect of
reduced Aw on the vegetative cells of Staph, aureus (10).
Studies have been done which exhibit the protective
or antagonistic effect of various food constituents on
microorganisms.
For example, sugars generally have a more
protective effect on microorganisms than does NaCl.
However,
E. coli and Staph, aureus tend to have more resistance to
thermal destruction when NaCl is available in comparison
to sugar (20, 63).
One study submitted that the medium in
which salmonellae are grown has little or no influence on
the heat resistance of the organisms (52).
Many other
researchers in the area agree that, on the contrary, most
microorganisms are influenced either positively or
negatively by the food components, including, fats, proteins
and carbohydrates (64, 66, 67, 68, 69, 70).
These effects
are noticeably variable.
The effect of the food components is in part due to
the temperature of the menstrum.
S,. typhimurium would grow
in higher percentages of milk solids at higher temperatures
than at cooler temperatures (71) .
Ingredient effect is a
29
total phenomenon.
This is exemplified by the fact that egg
protein will be more or less protective depending on the
other ingredients present (19, 72).
Pure proteins had little
effect on salmonellae in one study.
Peptides ,and amino
acids provided only a minor amount of protection during heat
treatment (64).
Katamey and Khan found that fatty acids
and triglycerides were bacteriocidal for salmonellae immedi­
ately with no additional changes after one week in the recov­
ery medium (73) .
Pertinent research with egg proteins and .
milk solids verify the protective effect they may have in a
heated medium (19,
.71, 72, 74, 75).
Evidence from several
studies points to the fact that whole milk gave more protec­
tion for bacteria than all other substances tested, includ­
ing various peptide mixtures,' salts, or carbohydrates (24,
64).
NaCl, as a common food element, has an influence on
the thermal resistance of bacteria.
For example in one
study, NaCl was responsible for thermal resistance six
times.greater than sugar for salmonellae in similar
products.
Glauert and Cotterill state this resistance was
not explained by the viscosity of the solution, but possibly
by cell dehydration (76).
The effect of NaCl is in part
determined by the temperature of a medium.
Low levels of
30
NaCl (I to 4 percent) stimulated the growth of salmonellae—
the most stimulation occurring at temperatures lower than
optimum for the microorganism (12 C.).
Such low concentra­
tions are probably not sufficient to prevent growth at
higher temperatures (37 C.).
NaCl concentrations of 7 to 8
percent caused growth increases at temperatures of 37 C . (77).
High NaCl concentrations (up to 12 percent) decreased the
production of staphylococci enterotoxins B and C to undetect­
able levels in a study by Genigeorgis and his coworkers
(14, 78).
The production of staphylococcal toxins was not
influenced by the presence of NaCl in one study (8).
Preservatives may have some effect on the thermal resistance
of bacteria (79, 80), but this effect is not.well understood.
A realization of the effect of ingredients on bacter­
ial survival must necessarily include the potential bacter­
ial status of raw materials put into food.
Casseroles are
particularly susceptible to many sources of organisms due
to the array of constituents used.
Sea foods are an
excellent raw medium for bacterial growth (81).
Raw
vegetables, on the other hand, are seldom a problem because
a cooking period long enough to soften the tissue is ade­
quate to destroy surface bacteria.
Acid-forming microorgan­
isms on vegetable surfaces are competitive to salmonellae
31
(15).
Meat products are of special importance in bacterio­
logical quality because raw meat is a good growth medium
for many harmful organisms.
Studies with C. perfringens
showed that 82 percent of veal cuts tested harbored this
organism (48).
Slanetz claimed that other raw meats con­
tained C . perfringens as much as 17 percent of the time
(82), and in 16 percent of all cuts examined in another
study by Strong and her group (83).
Staph. aureus was
found in the highest incidence in pork chops (84).
Salmon-
ellae were isolated in high numbers from poultry, raw pork,
and carcasses of other animals (12, 85, 86).
The incidence
of salmonellae on poultry products from the initial process­
ing stages to the retail market stage showed a stable
occurrence of the organism at all points.
The percentages
in finished products ranged from 12 percent to 58 percent
(85, 87, 88, 89, 90, 91, 92, 93, 94, 95).
The role of the individual ingredients or the various
foods in combination is not completely clear.
That is,
from the ingredients in a given food one cannot evaluate
the total protective effect of a menstrum upon a micro­
organism.
Dega et al. have suggested that S . typhimurium
and other bacteria be tested in every-food environment in
order to understand the varied and total effects of a food
32
substrate on an organism (71).
Competition of Microorganisms
Another factor which constitutes a viable safety
mechanism in foods is that of naturally occurring competi­
tion of the food flora.
recent importance.
This factor is one which has gained
Augmenting the aforementioned factors,
natural bacterial competition affects the ability of a
species to multiply.
In a mixed bacterial population,
organisms may stimulate or inhibit other organisms.
In a
discussion of bacterial competition, it should be noted
that the competitors are considered to be the natural flora
of the food.
Food poisoning organisms are common flora on
some foods, but are not considered desirable inhabitants
of processed foods and could thus be considered to be
foreign organisms to these foods.
Results of studies indi­
cate that competing bacteria (natural flora) most generally
have an inhibitory rather than stimulative effect on
foreign microorganisms.
The full effect depends on all
environmental conditions (96).
" inhibition may be due to
competition for amino acids or other nutrients.
Some
species such as B. cereus, E. coli, or Proteus vulgaris may
produce antibiotic substances which inhibit other species
33
such as Staph, aureus.
Staph, aureus requires cystine,
valine, glycine, proline, arginine, and aspartic acid.
Serratia marcesaris and Pseudomonas species inhibit Staph.
aureus by outcompetihg it for these nutrients.
Competition
for any of these amino acids will inhibit the species (97).
The acid produced by the lactic acid microorganisms has
value as an inhibitory substance for food poisoning strains
which prefer a pH near neutrality (98).
Indications are
that the depletion of vital nutrients by competitors is a
more important factor than the total proportion of Staph,
aureus compared to competitors.
Another major factor in
the competition with Staph, aureus is the depletion of
nicotanamide.
Certain other organisms, if present, will
metabolize this compound at a high rate, leaving insuffi­
cient amounts for Staph, aureus (99).
Oxygen availability
seems to be of little importance for competitive strains
grew equally well in the center of the food mass as well as
at the surface.
There appears to be an indirect relation­
ship between the concentration of effectors and the rapidity
of retardation of foreign organism (100).
Peterson et al. stated that the possibility of
staphylococcal.food poisoning occurring after the consump­
tion of a food containing mixed bacterial populations is
34
very limited.
The competitive inhibition will, most likely
occur between freezing temperatures and room temperatures
(101).
In the range of room temperature (about 25 C.) to
37 C . the saprophytic spoilage will render a product inedible
in less than 24 hours.
viable
In this way it is unlikely that a
staphylococcal population would be consumed (102).
Very seldom was a staphylococcal population of IO^ organ­
isms per milliliter obtained when a food menstrum contained
approximately equal numbers of repressors and inocula (100).
Ingredients play a role in bacterial competition
also.
This is an indirect asset to competitively destroying
Staph, aureus.
On the other hand, the role of ingredients
in competition may be a favoring of growth of pathogens.
This is demonstrated by NaCl concentrations which selecr
tively inhibited competitors
of Staph, aureus allowing
profuse growth of the food poisoning organism (103).
Sap­
rophytes were retarded at all NaCl concentrations, while
staphylococci survived well at high NaCl concentrations at
20 C., 30 C., and 37 C .
The NaCl enhanced the staphy­
lococcal population, while simultaneously repressing
saprophytic growth.
This decline in the competitor’s
ability to survive is contrary to the evidence mentioned
earlier, again showing the variability of all factors in
35
the ability of organisms to survive in foods.
Quality of the Finished Product
There are several places in the preparation of food
where contamination is most likely to occur.
The original
raw products can add numerous bacteria of an undesirable
nature.
During the processing stage, food handlers and
utensils offer a potential source of unwanted organisms.
Proper cooking procedures should eliminate organisms from
these two sources.
contamination.
The last major source is post-cooking
In a discussion of processed foods, one
must consider the quality of the raw products,. the prepara­
tion stage, and the quality of the finished product.
This
section will concern itself with the bacteriological
quality of the end product.
There is not an abundance of
research in this area.
One survey carried out by Jopke and Riley in the
Minneapolis-St. Paul area involved itself with the quality
of foods served from various cafeterias in the surrounding
districts.
Laboratory tests were done on such foods as
creamed turkey, chow mein, noodle casseroles, and macaroni
and cheese.
No salmonellae or C . perfringens were found
in any of the dishes tested.
Staph, aureus was found in
quantities of less than ten per gram which are numbers
36
considered too small to be associated with disease out­
breaks.
Total counts varied from less than 300 per gram to
10® per gram (104).
Imitation sandwich spreads were found
to be poor bacteriological growth media in another study.
Salad-type fillings for sandwiches had a much higher inci­
dence of microorganisms than did cheese or ham fillings
(105).
A study of salads and sandwiches at retail outlets
showed that 29 percent of the salads and 60 percent of the
sandwiches contained coagulase-positive staphylococci.
Salmonella and C. perfringens were found in much smaller
numbers (106).
A Kansas study deomonstrated an incidence
of 3.5 percent coagulase-positive staphylococci in frozen
cream pies (107).
Preparation as a Factor in Food Contamination
Microbial contamination can occur consistently during
food preparation depending upon the practices employed.
Good sanitation habits are an essential to any food estab­
lishment, and poor sanitary practices are a prime factor
in food poisoning outbreaks.
Consequently, good food hand­
ling procedures are a major preventative force in large ' •
quantity food establishments. A good sanitation program
must include control of both primary and secondary sources
37
of contamination.
Primary control measures include the
food handler himself, the food source, air, water, insects,
and rodent contamination.
Secondary sources are things such
as equipment, utensils, and physical surroundings such as
walls and.other surfaces (2).
Man is a major source of microbial contamination.
The average person in good health is a common reservoir of
Staph, aureus and enterococci in the throat, mouth, and
nose.
A survey of fifty healthy food handlers showed forty
harbored Staph, aureus.
Of these staphylococcal isolates,
90 percent were from the nose, 34 percent from the hands,
and 28 percent from both (108).
showed no salmonellae.
Feces of 219 food handlers
However, 78 percent showed C . per-
fringens and 80 percent E . coli (75).
Prepared foods had
•much higher counts than strictly fresh or raw foods, thus
substantiating the implication of food handler contamination
(109).
The personal habits of food workers are. very
difficult to control.
There are endless opportunities for
a worker to contaminate his hands— either from touching his
own body or from contact with other surfaces ( H O ) .
ing can be a potential
hazard
Cloth­
in food sanitation because
dangerous organisms can persist on fabrics under normal
working conditions.
Staph, aureus was tested on several
38
textiles and was found to survive best at room temperature
(25 C .) with a 35 percent relative humidity.
Organisms did
survive on cotton sheeting and, other cottons (111) .
S1.
typhimurium survived the least time on wash and wear fabrics
and cottons (112) at the same relative humidity (35 percent)
and at room temperature.
The potential hazards of mistreated equipment cannot
be disregarded.
The danger lies in the careless misuse
given them by handlers.
Several days of outbreaks in a
Naval station were traced later to a contaminated cutting
board.
Turkey had been thawed on the board so juices
remained on it.
The failure to clean it led to later food
poisoning outbreaks because.the cooked meat was sliced
on the already contaminated board (113).
dishcloths
Such items as
and other cleaning supplies can be the subtle
source of harmful food organisms.
Although there is a
tendency to assume that disposable towels are sterile, this
was found not to be so.
Total counts on unused handwipes
were less than 100 organisms per gram.
many as 7,206 organisms per gram.
Others contained as
Of this flora, 90 percent
were found to be Bacillus species (114).
Some caution
should be used when handling these handwipes around foods.
Nelson did a study on restaurant counter cloths and found
39
counts of more than one million organisms per four square
inches.
The organisms were mainly yeasts and molds, al­
though some coliformsf staphylococci and enterococci were
found (115).
Food preparation practices play a role in the pre­
sence or absence of harmful organisms in a prepared food.
Some preparation methods can decrease the possibility of
bacterial contamination more than others.
For example-,
fewer salmonellae were found in poultry if it was deboned
immediately after cooking instead of being cooled before
deboning.
The incidence was greater even if the food was
held at 3 C. or -15 C. for as long as nine months and then
deboned (116).
Sandwiches made from filling, cooled
several hours, showed less bacterial contamination than those
from fillings spread immediately after being made (105).
The importance of complete food sanitation is clear.
Good sanitation is the responsibility of both the worker
and the food supervisors.
Food service establishments have
attempted sanitation programs with success.
The supervisor
must help the worker to appreciate his extreme importance in
the health of the numerous people in the food chain.
sanitation program should not limit the food handler.
A good
If
well done these courses should create a cooperative attitude
40
where rules become habits.
Courses in food safety are
potentially valuable, and will be successful only if well
administered.
Employees may reject any education if they
are insulted or their role is negated, and thusly any
cooperative effort is discouraged.
One observer has form­
ulated some pertinent questions concerning the appropriate­
ness of food safety courses (117):
1.
Is the time allotted adequate to cover the
essential material?
2.
Is the information recent?
3.
Is the supervisor involved?
4.
Is the information put to practical application?
5.
Are the instructors good and do they show
interest in the material they are presenting?
Etiology of Some Specific Outbreaks
The etiology of outbreaks in various institutions is
important for stimulating awareness of foodborne illnesses
and thusly preventing recurrences.
Bacteria exhibit no
discrimination— that is, they may strike at penal institu­
tions, college cafeterias, cafes or hospitals.
One hundred
persons in a Michigan prison were afflicted by SY enteriditis.
The cause was cross-contamination due to poor
handwashing facilities, poor lighting, worn cutting boards,
and inadequate heating of the foods involved (118). ' S .
41
newport was isolated in a. New Mexico mental hospital after
a Thanksgiving dinner in which inadequate time and tempera­
ture were used to roast turkey (119).
Multiple contamina­
tion by S . thompson occurred in a church supper which
affected 200 people.
Chicken was thawed and handled
improperly, and the potato salad and bread dressing were
infected (120).
Persons numbering 303 were left ill
following the consumption of barbecued pork in a restaurant.
S. thompson was present due to improper facilities and
procedures, and poor sanitary practices which allowed
survival, dissemination and replication of salmonellae
(121) .
Soiled linen and poor hand washing procedures were
responsible for five deaths and 43 illnesses in a Michigan
nursing home.
(122) .
S . typhimurium was the prevalent isolate
These aforementioned outbreaks have all occurred
within the last three years.
.The importance of careful handling of food cannot be
stressed enough.
In recent years, 99 percent of all
reported cases of staphylococcal and salmonellae outbreaks
were due to cooked high protein foods.
Leftovers were
responsible for 94 percent of outbreaks (12.3) .
A salmonel­
lae outbreak involving 390 persons in Kentucky was due to
undercooked turkeys,
These were later used to make creamed
42
turkey (124).
An outbreak at, the University of Wisconsin
was due to C. perfringens in the gravy.
Day old beef stock
was stored overnight in nine gallon containers which could
not cool properly.
This stock was then added to new gravy
and boiling was inadequate to eliminate the danger (125).
Adequately prepared foods are unlikely to harbor C. perfrinqens (83).
Poor handling of turkeys both before and
after cooking, allowed growth of S. typhimurium and
perfrinqens.
(126)o
C_.
The same infected food was reused three times
Staph, aureus was isolated from a chicken salad
from a school cafeteria serving 6,000 children.
Intoxica­
tion occurred in 1,300 students because the salad was not
properly chilled from the time the chickens were deboned
until they were served (127).
Summary
The growth of harmful pathogens is affected by a
rather complex set of environmental conditions.
These
factors are so interrelated that it is impossible to discuss
one without the other.
Temperature is probably the most
important overall influence.
It influences all other
factors such as competing natural flora, ingredients and
water activity.
Raw materials are important for the natural
43
flora they represent as well as their role as an ingredient
factor with protein, carbohydrate or fat components.
The
total, effect of these factors will be the determinant of
whether microorganisms can grow.
With so many factors hav­
ing influence, it is impossible to make any all-inclusive
rules concerning time-temperature for all foods.
Foods prepared in a food service establishment must
progress through several stages.
The cooking zone is
essential to destroy pathogens and the holding zone should
prevent multiplication though it does not usually destroy
organisms.
The chilling zone also should prevent increases
in numbers•over an extended period and probably counts will
decrease.
The danger zone is between the chilling and the
cooking zone, and public health regulations designate that ■
food should not be held in this zone any longer than
possible.
This zone is in the temperature range, wherein
foods are most susceptible to bacterial growth.
Proper sanitation practices are another essential
which cannot be overlooked as a factor in determining food
safety.
Food handlers are the ultimate factors in food
safety for they can choose quality ingredients which go into
a food.
They can also control other factors like temperatures
used and cleanliness of equipment.
They must be given
44
proper consideration in any program of food sanitation.
The following study is intended to consider the
food sanitary practices as a factor of food safety.
A good
measure of proper food safety is the bacteriological quality
of the food itself following preparation.
Casseroles were
selected, as they represent a wide array of ingredients,
handling procedures, and heating— several opportunities for
the inclusion of pathogens.
The dishes were evaluated
microbiologically for incidence of Staph, aureus, Salmon­
ella, and C . perfringens.
CHAPTER III
METHODS
This study is concerned with the qualitative micro­
biological evaluation of certain dormitory cafeteria hotdishes as an indicator of the sanitation practices in such
a facility.
The casseroles were selected for testing because
their preparation encompasses a series of potentially
hazardous steps in which contamination might occur.
The
making of a casserole involves a variety of raw goods , a
substantial amount of human handling, and a heating process
of some degree.
Carelessness in one or more of these steps
could result in a final product with harmful bacterial
growth which is dangerous for human consumption.
The
casseroles selected for bacteriological examination were tuna
noodle, beef stroganoff, and pork chop suey.
Each dish was
sampled from the cafeteria line, at the point, where the food
reaches the consumer.
The purpose of the study was to
evaluate the lengthened serving hours now observed in the
cafeteria to see if the extended hours are of danger rela­
tive to maintenance of food safety.
These augmented serving
hours were instituted in the Montana State University food
services in January of 1970.
Foods are now served weekdays
for eleven hours of the day compared to earlier totals of
46
six to seven hours.
There is an obvious lack of pertinent
research in this particular area.
This is partly due .to the
fact that this trend in food service management is rela­
tively recent.
At the present time, the lunch meal is
served from 10 a ^m. until 2 p.m. Mondays through Saturdays.
The dinner meal begins at 4 p.m. and extends until 6:15 p.m.
Mondays through Saturdays.
study.
Sundays are not included in this
All the methods used for the experiment were accept­
able methods and they will be reviewed in this section.
Preparation of Casseroles
Recipes of the casseroles studied are included in
Appendix A.
The methods all include a period of heating
from one to one-and-one half hours in steam kettles in order
to tenderize the ingredients, and distribute the flavors.
At this point, the tuna noodle casserole was baked in the
oven at 232 C.
The other two dishes, once in serving pans,
were not baked but were maintained in the thermal units
directly behind the line until needed.
these electric units is 66 C .
The temperature of
The steam tables are main­
tained at 82 C. in order that the food may be kept above
60 C.
47
Collection of Sample
Samples were gathered on each day that tuna noodle
casserole, beef stroganoff, or pork chop suey appeared on
the menu of one college cafeteria during the months of
December, 1971, and January through April of 1972.
The
particular unit feeds approximately 1,760 students of both
sexes.
The particular dishes were offered at either lunch
or dinner meals.
During the meals when these casseroles
were offered, a total of four samples were gathered.
initial sample preceeded the actual meal time.
The
The
remaining three samples came directly from plates served at
the cafeteria line.
Sample one was taken during the final
preparation stage; that is, while the food was still in the
steam kettles, heated, and ready to,be put in serving pans.
The first sample was taken from fifteen minutes to I 1/2
hours before the meal period.
Other samples followed at
half hour to two hour intervals.
Variations in the time of
the initial sample were due to the type of food or situa­
tional delays in preparation.
Beef stroganoff, for example,
could not be sampled until the sour cream was added and the
entire mixture was reheated.
The sour cream was added as
close to serving time as possible to prevent prolonged
heating and thus separation of the cream from the mass.
48
This eminent procedure made it mandatory that the first
sample be taken just a matter of minutes prior to the meal.
Each time one of the casseroles was offered, the supervisor
was consulted in order to determine the best time to gather
the first sample.
The remaining samples were gathered at
the following times with a ten minute variation:
Noon Meal:
10:15 a.m.
Evening Meal:
4:10 p.m.
12:15 p.m.
1:30 p.m.
5:05 p.m.
6:10 p.m.
The utensils used were a sterile bowl, a sterile
spoon, and sterile thermometers.
The mechanics.of the
sample collection were as follows:
the first sample was
gathered from the steam kettle and put directly into a
sterile bowl.
The temperature was taken immediately.
All
other samples were taken from plates served from the line.
The temperature was taken at once.
Subsequently, the food
was placed in a sterile bowl and covered.
In all cases,
bowls were put immediately into a pan containing ice, and
transported back to the laboratory.
At this point, the
sample, still on ice, was put into the refrigerator and
maintained until plating could be initiated.
The time lapse
from collection until testing was usually three hours, and
never exceeded eight hours.
49
Preparation of Homogenate
Immediately before blending, the sample was stirred
with a sterile thermometer to distribute any bacterial
constituents, and the time and temperature were recorded.
Sterile utensils were used to weigh out two fifty gram
portions.
These portions were initially blended with 450
ml. of 0.1 percent sterile Peptone Water (Difco), and 450
ml. of sterile Lactose Broth (Difco) which resulted in
1:10 dilutions.
Many diluents have been used with varying
degrees of success— such as phosphate buffer, Ringer's
solution and distilled saline.
A general purpose medium of
growing favor is 0.1 percent Peptone Water (6), which has
given accurate recovery without, toxicity for common food
poisoning organismx (128, 129, .130, 131, 132, 133) .
The homogenate was formed by blending at high-speed
in a one quart sterile Waring blender for two minutes as
recommended by Thatcher (6) and the National Research
Council (NRC)
(132).
Avens and Miller found that blending
times of I, 2, 3, or 4 minutes showed no significant
variations in results (131).
In this particular study, a
two-minute blending time did not cause a temperature
difference greater than 4 C. from the temperature of the
50
sample and Peptone prior to blending.
The mixture was
allowed to sit 15 minutes before further dilution and plat­
ing so organisms could resuscitate.
Longer waiting periods
have been reported to cause die-off of cells (123).
The
1:10 Lactose mixture was blended, placed into a sterile
beaker, and incubated for 24 hours to allow growth of
possible salmonellae before selective enrichment.
The
Peptone mixture was used to make dilutions for all other
organisms.
Temperatures for preparing the homogenate are not
specified.
One source recommends use of "ambient" tempera­
tures of the product and the diluent (132).
Abiding by this,
all diluents (Lactose and Peptone) were kept at refrigera­
tion temperatures at least eight hours prior to blending.
In this way, the difference between temperatures of food and
diluent was not great enough to have shocking or deleterious
effects upon the bacteria present in the food.
Additional
dilutions were made according to methods as suggested by
Thatcher (6) and Standard Methods for the Examination of
Dairy Products (APHA)
(134).
Aerobic Mesophilic Plate Count
Aerobic mesophilic plate counts are generally used for
determination of the portion of bacteria in a food which are
f
51
able to grow in a medium temperature range and in normal
atmospheric oxygen (6).
Standard Plate Count Agar (PC,
Difco) was used as recommended by Thatcher (6), APHA (134),
and NRC (132).
The pour plate method was selected for use
here, and plates were incubated at 37 C . After 48 hours
incubation plates were counted on a dark-field Quebec Colony
Counter.
Plates with more than 30 and less than 300 colon­
ies were counted.
The number of mesophilic aerobes per gram
of food were calculated.
The standard plate count is valued
as an indicator of general sanitary adequacy in the prepara­
tion, transport and storage of foods.
This method is used
almost exclusively in North America (6).
Coliforms
"Coliform organisms, faecal coliforms, and E. coli
are primarily used to indicate some degree of potentially
hazardous contamination... E . coli is generally accepted as
the most positive indicator of faecal contamination"(6).
Coliforms are good indicators of unstored or briefly stored
foods as compared to faecal streptococci which are more
reliable indicators in long-term stored foods (135).
Coli­
forms are usually present in very high numbers in cases of
foodborne disease.
For this reason they seem to be good
indicators of unsanitary foods (45, 136).
An average of
52
10 coliforms per gram is acceptable for most foods (134).
Research on sandwich spreads found coliforms generally
proportional to total plate counts (105).
The coliform
group includes aerobic and facultative anaerobic gram nega­
tive nonsporeforming rods capable of fermenting lactose with
the production of acid and gas at.32-35 C. within 48 hours
on solid or liquid media (134).
For this study, Brilliant Green Lactose Bile Broth-2%
(BGLB,BBL) was used for presumptive tests as recommended by
the APHA methods for the examination of dairy and related
products (134).
BGLB has been supported as the standard for
the examination of milk products as well as other products
(109).
One milliliter aliquots of the blended homogenate
were dispensed into tubes with 10 ml. of..BGLB prepared with
fermentation tubes.
Three tubes per dilution were inoculated
in order that Most Probable Number (MPN) calculations could
be done.
Incubation temperature was 35 C .
In one study, it
was found that lower temperatures of incubation such as
20 C . and 32 C . produced results comparable to 37 C. in
products tested (137).
Gas formation within 48 hours is
indicative of a positive test.
Tubes positive were streaked
onto Eosin Methylene Blue (EMB, Difco) and Endo (BBL) agars
for confirmation (6, 13, 134).
Positive results were
53
indicated by translucent colonies with dark centers on
EMB, bright pink colonies on Endo, or black colonies with
fluorescent reflection on either agar.
Staphylococcus
The NRC Subcommittee on Methods for the Microbio­
logical Examination of Foods states concerning staphy­
lococci , "There is insufficient basis for recommending a
reference at this time" (132).
There is some current
discussion as to the effect of a recovery medium on cell
recovery, "the presence of inhibitors or other selective
agents in a medium may markedly reduce its productivity"
(19).
Damaged cells are more exacting in nutrient demands
(61, 62).
The recovery of Staph, aureus requires glucose,
amino acids, and organic phosphate (1.7) .
not seem to help Staph, aureus
psychrophiles (138).
Yeast extract did
(41) but did aid competing
There is some feeling that Staph.
aureus loses its ability to grow in NaCl concentrations of
7.5 percent after heat damage (139).
In one study it was
shown that Staph, aureus would recover in 5 percent glucose
or galactose but not in NaCl, thus making Staphylococcus110 (S-110, BBL) an adverse medium (140) .
Tellurite may
also cause a reduction in numbers of thermally damaged
cells (19).
There are several accepted methods which make
54
use of NaCl solutions, sodium tellurite, egg yolk and other
selective agents.
For this study, an enrichment step utilized Difco
Tryptic Soy Broth (TSB, Difco) with 10 percent NaCl. One
milliliter aliquots of the blended homogenate were put into
each of three tubes per dilution.
48 hours at 37 C . (6).
Tubes were incubated
Although some studies indicate that
Staph, aureus 'has decreased ability to recover in NaCl
medium following thermal damage, others agree that enrich­
ment in 10 percent NaCl gives higher recovery than direct
plating.
NaCl concentrations of 12 percent have been found
detrimental (141, 142).
After TSB was incubated 48 hours, one loopful of
broth from each tube was streaked onto Vogel-Johnson (VJ7
Difco) and S-IlO (BBL) Agars.
It is preferable to use a
highly selective medium (such as VJ) in addition to a less
selective one like S-IlO (6).
"No medium is ideal for•
maximum recovery of Staph, aureus" (39).
The VJ preparation
contained 5 ml. per liter less tellurite than commonly used.
Manufacturer1s directions suggested this variation in the
amount of tellurite.
Studies with VJ show that it did not
permit the growth of five other species tested (39) , but
showed regular recovery of coagulase positive staphylococci
55
from frozen foods of animal origin (141).
Other workers
have found VJ to be inhibitory for staphylococci present
in very small numbers (143).
For recovery from meats, it
was found to be the least effective of six media (144).
Proteus vulgaris will grow on a tellurite agar with black
colonies similar to those of Staph, aureus (145).
In the current study, colonies appearing positive
on selective agars were streaked onto Nutrient Agar (NA,
Difco) and stored until coagulase tests were performed.
For
coagulase tests, growth from NA was inoculated into Brain
Heart Infusion Broth (BHI, Difco) and incubated for 24 hours
at 37 C .
Small tubes were filled with .5 ml dehydrated
Difco Rabbit Plasma.
These were inoculated with two or
three drops of the 24 hour
BHI cultures.
Tubes were
incubated in a 37 C. water bath for a total time of four
hours.
clot.
Tubes were checked hourly for the formation of a
A distinct clot was considered positive evidence
for the presence of coagulase positive staphylococcal
organisms.
Salmonella
The method used for isolating salmonellae involved
a pre-enrichment step, selective enrichment, and selective
agars.
Some researchers feel that all steps are essential
56
to the recovery of thermally damaged cells— "Elimination of
any step would probably yield erroneous results since test
organisms show sensitivity to both enrichment and selective
media"
(146).
The NRC Reference Methods (132) recommends
pre-enrichment for processed foods where salmonellae may be
injured.
Pre-enrichment was preferred to direct inoculation
by other investigators also (147, 148).
For this study, Lactose Broth was used for the pre­
enrichment medium.
Studies have shown Lactose Broth to be
the preferred medium (146, 147) , except where coliform ratios
are extremely high (149).
Taylor and Schelhart found pre­
enrichment to be valuable when foods contained highly
soluble proteins like albumin which could nullify inhibitory
action in tetrathionate and selenite enrichment broths (150).
Mannitol has been recommended as a better enrichment sugar
than lactose (151).
The Lactose Broth was incubated at 37 C . for 16-24
hours.
It was then inoculated in one gram portions into
two tubes each of Selenite Cystine (SC, Difco) and Tetrath­
ionate Broth (TR, 'Difco) .
iodide solution.
The latter broth contained an
Selective enrichment broths were incubated
24 hours at 37 C. (6).
Selective enrichment has been found
to give a two-fold increase in salmonellae isolations (151) ..
57
Selenite Cystine gave the most favorable results in chicken
studies (89).
In another study Selenite produced better
results than Gram Negative Broth, Tetrathionate, or Kauffman
Mueller (150).
Enrichment in Selenite gave 99 percent yield
when direct streaking on agars was used (152).
The substi-
tution of mannitol or dulcitol for lactose in Selenite
produced an increase in the number of isolations (153).
Tetrathionate was found more successful than Gram Negative
Broth or Selenite (146, 154) for the recovery of heat
injured S . typhimuriurn.
Tetrathionate with iodide was more
inhibitory to E, coli, although iodide had no significant
role in the lethal action of tetrathinate in a study by Dunn
and Martin (155).
Tetrathionate and/or Selenite are recom­
mended by the major authorities of standard methods.
Most
suggest the use of both broths (6, 132).
Selective agars used for this study were Brilliant
Green Agar with Sulfadiazine (BGS, BBL) and Xylose Lysine
Deoxycholate Agar (XLD, BBL).
One loopful of each selective
enrichment was streaked onto the agars which were then incu­
bated for 48 hours at 37 C .
Numerous studies have been done
comparing.various plating media used for salmonellae.. The
organism is more frequently isolated when more than one
medium is used due to the increased probability of recovery
58
and the qualities of the medium used (156).
Several studies
haye found XLD to be very efficient more so than EMB or
Salmonellae-Shigella (SS) agars (151).
It produced 94
percent yield compared to lower yields of other agars
including MacConkey's (150).
Other investigators have found
XLD very satisfactory if made-in the laboratory but giving
poor recovery from commercially made XLD (151).
XLD
decreased the number of false positives in one study (154).
XLD has produced reasonably reliable indications of salmonellae (157) while no significant difference was found
between BGS and other media tested (158).
For this study, positive appearing colonies on BGS
and XLD were streaked onto MacConkey's agar for isolation.
Researchers showed that heat treated cells show no sensiti­
vity to MacConkey's
(146), this agar utilizing lactose as
a fermentable carbohydrate.
48 hours at 37 C .
Plates were incubated up to
Positive colonies were streaked onto
Triple Sugar Iron Agar (TSI, Difco) and likewise into
Gillies Medium I and II (Difco).
Agglutination tests were
performed in cases where biochemical results were indicative
for salmonellae.
Salmonellae Polyvalent Antiserum A-I (BBL)
was rehydrated with .85 percent saline for agglutination
tests.
A definite granular-like precipitate was considered
59
to be positive for salmonellae.
Clostridium perfringens
The pour plate method was used for this study.
Mead
has shown this method to be the best for C . perfringens
(159).
Trypticase Sulfite Neomycin Agar (TSN, BBL) was
selected for this study.
Other investigators have shown TSN
to be superior to other media-broth both qualitatively and
selectively (160).
In one study TSN was superior for
identifying C. perfringens in pure cultures, and chicken soup
(108).
While TSN was most inhibitory to microorganisms
other than C. perfringens (161), Smith found it gave 96
percent recovery of C. perfringens.
Indications from one
study are that counts on TSN were somewhat lower due to
inhibitory action of this agar (162).
Sulfite Polymyxin
Sulfadiazine Agar (SPS) was shown to give low recovery (59)
and especially if commercial lots were used (133).
The pour plates, including control plates, were over­
laid with TSN Agar for this study.
All were incubated in a
Thomas Stainless Steel Anaerobic Jar.
The jar was filled
with a 90 percent nitrogen and 10 percent carbon dioxide
mixture and incubated no less than 24 hours at 37 C .
Typr
•ical black areas of sulfite reduction were considered posi­
tive for C . perfringens in addition to accurate gram stains.
TT-
60
Positive colonies were inoculated into Fluid ThiOglycolate
for three hours in a 46. C . water bath.
At the end of this
period, a stab was made into Motility Nitrate Medium.
Gram
positive blunt rods which exhibited no motility were con­
sidered to be C,. perfringens.
Treatment of Data
For the total aerobic mesophilic counts, all plates
with colonies numbering between 30 and 300 were counted and
averaged.
The organisms per gram of food were then calcu­
lated.
Coliform counts were determined by the Most Probable
Number (MPN) technique.
A MPN table for a triple dilution,
three tube test gave the MPN value for the number of posi­
tive tubes.
The following formula was then used to find
the number of coliforms per gram (6):
MPN value
100
__
" x
Dilution of the
middle tube
=
MPN per
gram
No quantitative evaluation of the salmonellae or
staphylococci data was made.
Plates were recorded either
as positive or negative and then confirmed.
C. perfringens
colonies were counted, and the total counts per gram were
ascertained similar to the method used for the aerobic plate
counts.
CHAPTER IV
RESULTS AND DISCUSSION
The total standard plate counts for pork chop suey,
tuna noodle casserole, and beef stroganoff at all sampling
times were rather low as shown in Table 4, page 62.
The
acceptable standard for similar foods is 100,000 organisms
per gram and less than 10 coliforms per gram .(4).
The
range of total counts for all dishes in this experiment was
2 bacteria per gram to 1500 per gram.
the highest average total counts.
Pork chop suey had
This average was higher
due to relatively high counts which occurred on one day on
which this particular dish was sampled.
On other days pork
chop suey exhibited consistently low counts.
The beef
stroganoff and tuna noodle casseroles produced consistently
low counts.
The ranges for beef stroganoff for all days
tested was 2 organisms per gram to 19 per gram, while tuna
noodle showed variation from 7 bacteria per gram to 101
per gram.
Pork chop suey counts ranged on all days from 2
bacteria per gram to 1500 per gram.
The counts were
generally low enough and so consistent that no trends over
the time periods studied can be formulated.
be accounted for by experimental error.
The ranges can
For example, beef
stroganoff had a low standard deviation with the highest and
Table 4
COMPARISON OF PLATE COUNT AVERAGES OF FOUR SAMPLING
TIMES OF THREE CASSEROLE-TYPE DISHES SERVED
IN ONE COLLEGE CAFETERIA
Time of Sample
Plate Count Averages and Standard Deviations
Tuna Noodle
organisms/gram
Beef Stroganoff
Pork Chop Suey
organisms/gram_____organisms/gram
Before Meal Sample
33 ±4.7a
14+4.2
3951638.6 (26123.5)
First Meal Sample
62±20.7
12+2.9
2121332.1 (19l9.8)b
Second Meal Sample
28±10.3
13±9.4
155±248.4 (12±8.6)b
Third Meal Sample
67-34.9
4-1.1
76±109.2 (13±3.1)b
aNumbers are averages of four determinations
^One run of pork chop suey produced plate counts which were much higher
than other samples of the same product. Numbers in parentheses are
averages of plate counts exclusive of the one high sample. Standard
deviations are likewise given.
63
lowest counts varying by only 17 organisms per gram.
Tuna
noodle showed more variation with a difference of 94 bacter­
ia per gram between the highest and lowest counts.
These
ranges were considered to be too stable for all dishes to
lend consequential support to the thesis that the lengthened
serving hours are hazardous relative to the bacteriological
quality of the food being served.
As mentioned, the casseroles were sampled four times
on those days when they were offered on the menu.
The first
sample was taken when the food was being cooked.
The remain­
ing three samples were obtained while the food was at hold­
ing temperatures.
All dishes had the highest temperatures
during the cooking phase.
The average temperatures for each
dish at each time sampled are given in Table 5, page 64.
Beef stroganoff had the lowest holding and cooking temperat
ture averages with only 9 C . variation between the lowest
average holding temperature and the cooking temperature.
Pork chop suey displayed the highest temperature averages at
all sampling times.
Tuna noodle had the highest cooking
temperature averages.
Pork chop suey had the most consistent
.average temperatures with a five degree variation between
the highest and lowest temperatures.
The other dishes
showed a steady decline in average temperatures with a 13
64
degree decrease for tuna noodle and 11 degree decrease for
beef stroganoff.
Most of the cooking and holding tempera­
ture averages were below the Public Health Standards for
maintaining foods.
The average temperatures as shown in
Table 5 are quite constant and no discernible trends can be
established from these results.
Table 5
AVERAGE TEMPERATURES OF SAMPLING OF THREE CASSEROLE
TYPE FOODS SERVED IN A COLLEGE CAFETERIA
Time of
Sample
Tuna
Noodle
°C.
Beef
Stroganoff
°C.
Pork Chop
Suey
0C.
Before Meal
Sample
63a (45-72)b . 57 (49-64)
61 (49-74)
First Meal
Sample
55
(42-62)
54 (45-62)
56 (52-59)
Second Meal
Sample
55
(50-65)
51 (45-59)
60 (50-69)
Third Meal
Sample
50
(47-54)
46 (39-51)
61 (54-68)
aNumbers are averages of four determinations
^Numbers in parentheses give the range of the four,
temperatures used to figure the average temperatures
The beef stroganoff had the lowest total plate counts
as well as the lowest average temperatures during both
65
holding and cooking times.
able explanation.
This inconsistency has a prob­
The temperatures were low possibly
because the sample was collected after the addition of the
sour cream, immediately before the meal.
This would lower
the temperature of the mass and unless the sample was col­
lected when the mass had been entirely reheated, the temp­
eratures would be lower than adequate.
Also, the dish had
been heated at least I 1/2 hours prior to this which elimin­
ated most of the bacteria, and the sour cream would probably
not add a gross contamination so it was unnecessary to
reheat the mass to a high cooking temperature as previous
to the addition of the cream.
The sour cream and the
tomato soup in the beef stroganoff were likely influential
in the low counts occurring in this dish.
These ingredients
would lower the pH of. the food, and in combination with the
long cooking period, the opportunity for bacterial Survival
would decrease.
This could explain the very consistent
counts experienced in this casserole.
The high counts which
occurred in one run of pork chop suey could have been due to
a higher natural flora in one or several of the ingredients
used.
However, since the other three runs of that food
exhibited much lower counts, there was probably some minor
contamination from equipment, utensils or food handlers.
66
The rise in the one run of pork chop suey was particulary
noticeable.
Although these increased counts did not appear
to be due to one of the three pathogens sought, this does
not eliminate the possibility of danger.
It should be
recognized that this was probably not an event of chance.
Some flaw occurred in the processing of the food such that
a large bacterial load did result.
For this reason, this
one high run, despite, otherwise low counts, cannot be
deemphasized for such errors in sanitation, as occurred on
this day, could without doubt occur again.
The other low
counts do not erase the need for sanitary improvement.
This
experiment was not comprehensive for all foods on all days,
so similar high counts undoubtedly do occur periodically.
The danger this presents is obvious.
These facts acknow­
ledge that some concern is needed in surveying where sanita­
tion habits may be weak.
If one aspect of the sanitation
falls below standard, the food can be a crucial source of
problems.
Table 5 shows that only four of the average temper­
atures for all dishes surpassed the Public Health limits
for safety.
Temperatures between 7 and 60 C . (45-140. F •)
are considered to be in the danger zone (52).
important general guideline.
This is an
However, the decidely low
67
counts in the foods tested despite the low temperatures
merely emphasize the fact that bacterial survival depends
on a total set of environmental conditions— competitive
flora, pH, ingredients— as well as temperature.
Heating
is a standard because it is probably the final overall
factor when other factors are lending protection to micro­
organisms.
The amount of heat is also a measurable entity
while the effect of the other factors is not as readily
discernible.
The 60 C . (140 P .) limit does allow a margin
of safety (2).
Temperatures above 60 C . (140 F .) should
prevent the multiplication of most pathogens.
Elimination
of the major bacterial load is concurrent with a cooking
temperature prior to holding.
There is no definite agreement in the literature
concerning the best temperatures for eliminating bacteria
from foods.
However, most of the studies indicate tempera­
tures which are greater than the temperatures found in the
foods sampled in the current study.
Research by Miller and
Ramsden with meat pies showed that internal temperatures of
46-47 C. (114-116.F.) were the highest temperatures reached
before the outer crust became too brown in a 205 C . (400 F .)
oven.
However, one hour in a 160 C . (320 F .) oven caused
the food to obtain internal temperatures of 86.6 C . (188 F .)
68
(163).
Casseroles cooked for 40 minutes at 177 C. (350 F .)
reached internal temperatures of 57 C. (135 F .) at the end
of the baking and 63 C . (145 F.) after removal from the oven.
The number of bacteria was reduced at higher temperatures
but the casseroles were not sterile (164).
Chicken pies
baked at 218 C. (425 F.) required thirty minutes to reach
internal temperatures of 77 C. (170 F.) and forty minutes
to reach 101 C . (214 F.).
The latter temperature left only
neglible numbers of non-sporeforming organisms (49) . Longree
suggested that internal temperatures of 74-77 C. (165-170 F .)
should be attained terminally to destroy the common patho- .
gens.
Staggering the addition of the cold ingredients will
ease the load and make it easier to keep the mass above
60 C. (140 F.)
(2).
The interplay of all factors in a food mass may
eliminate the necessity for the. degree of heat usually recom­
mended, by authorities.
Nevertheless, as a measure of.
caution these temperatures are deemed valuable.
The temper­
atures found in this study were taken consistently and
accurately.
However, this does not negate the possibility
that the foods were not heated into a higher temperature
range than measured here.
The times of temperature taking
may not have been the peaks of heating for the foods
69
involved.
Also, there is the possibility that the cooking
temperatures need not be much greater than 60 C . (140 F.)
if the heating period is long enough.
Although the temperatures when sampled were rather
low, there would likely be little danger in storing and re­
using these foods judging by the low counts manifested even
when the temperatures were below 60 C . (140 F.).
These
considerations make it plausible that the foods tested did
at some time in their preparation achieve adequate tempera­
tures.
Most of the bacteria present were destroyed or
there would have been a more noticeable increase in the
counts in samples held below 60 C . (140 F .) for surviving
bacteria would begin to proliferate.
The total counts are
a reflection of temperatures which were probably quite
adequate but whose highest point was not concurrent with
the time of sampling.
Because the counts were so consist­
ently low, the probability of toxins being in the food is
small.
It appears that the bacterial load was eliminated
completely enough and early enough that a harmful■amount of
toxin would not be present in the food.
There has been some discussion about the effective­
ness of steam.tables and other holding equipment used in
food services.
Blaker found that food temperatures decreased
70
after two hours at 75 C . (170 F .) over a two hour period if
the steam table remained on (165X.
In another study, Blaker
found that electric holding cabinets held at 65 C . (150 F.)
may allow food temperatures to fall to temperatures as low
as 55 C. (130 F.) (166).
In the particular cafeteria under
consideration in the present study, the steam tables are
maintained at temperatures about 85 C. (180 F.).
The
thermal units in the same cafeteria are adjusted to 65 C.
(150 F.).
The higher temperatures on the steam table are
needed to assure that food is held around 60 C. (140 F.).
There was a definite absence of staphylococci,
salmonellae, and C. perfringens in the three dishes tested
in this study.
The coliforms incidence was very low also.
Although there need not be a positive correlation between
coliforms and the incidence of other organisms, it appears
to be the case in this study, wherein counts for all
organisms tested were so low.
The few colonies that early
looked like Salmonella were found later to be lactose
fermenters when streaked onto MacConkey's and TSI Agars.
Only two samples had any coagulase-positive staphylococci,
and these were from one run of pork chop suey in the last
two samples taken on one day it was served.
This meager
showing is undoubtedly too small an amount to be of conse­
quence in the total food mass.
71
Total time (hours) of a food being offered on the
serving line did not appear to change the counts noticeably.
That is, the noon meal is one hour and fifty-five minutes
longer than the evening meal and this did not seem to make
an increase in the total counts in any dish.
Tuna noodle
had the longest average sampling times--five hours from the
first to last sample.
The total average counts for all tuna
noodle samples were 52 bacteria per gram.
Pork chop suey
was served an average of four hours and the total average
counts were 218 organisms per gram.
Beef stroganoff was
served an average of 2.75 hours and the total average counts
of all runs was 9 organisms per gram.
Thus, there appears
to be no discernible relationship in the length of serving
periods and the average counts in any of the three dishes
of concern in this study.
To recapitulate, three casseroles— tuna noodle, beef
stroganoff, and pork chop suey— were tested for the
occurrence of pathogenic Staph, aureus, Salmonella species,
and C . perfringens.
The temperatures of the foods when
sampled were generally not within the Public Health Standards
for the safety of processed foods.
However, this does not
disavow the possibility that the food masses did attain
temperatures much higher at some time in their processing.
72
This is an acknowledgeable premise if one considers the low
occurrence of aerobic mesophilic counts and the Coliforms
and the negligible appearance of the pathogens being con­
sidered.
The length of a meal period does not seem to be
a factor in the bacteriological quality of the rfood if the
proper sanitation practices are carried out as presently.
The testing period varied in this study, from 2.75 hours to
5 hours on a given food.
The bacterial counts over the four
month period indicated no major danger in maintaining foods
warm for longer periods in the foods tested.
The experi­
mental results indicate a fairly good quality of sanitation
although increased
caution is warranted.
The longer
serving hours used in this cafeteria are not harmful as far
as the bacteriological quality of the foods served accord­
ing to the results found in this study.
CHAPTER V
SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS
Summary
This study has been concerned with evaluating the
sanitary quality of three casserole dishes in a dormitory
cafeteria service.
The study was done on the premise that
the new.longer serving hours now instituted in the cafeteria
on the University campus may be a hazard as far as the
bacteriological quality of the food served.
These new hours
necessitate that foods must remain at holding temperatures
for longer times than previously, as much as two hours
longer per meal.
The results would also be an indirect
indication of the sanitation practiced in the particular
cafeteria studied.
Food not maintained adequately for such
time periods could be a satisfactory medium for the pro­
liferation of harmful pathogens.
The consumers must be
protected from such foods, the consumption of which could
engender gastrointestinal illness of any degree in a sub­
stantial number of persons.
The pathogens of special Con­
cern in this study were Staph, aureus, Salmonella species,
and C . peffringens.
The results indicate that the food is not endangered
bacteriologically as an effect of the increased serving
74
hours now utilized in this particular cafeteria unit.
The range of total counts for all dishes was from 2 bac­
teria per gram to 1500 per gram.
Of these foods, beef
stroganoff had the lowest average counts (9 per gram) a n d .
pork chop suey had the highest averages.
The counts in all
runs of a particular food were very consistent with ranges
very small in beef stroganoff and greatest in pork chop
suey.
Temperatures of foods when sampled were generally not
above the 60 C . holding temperatures recommended by the
Public Health Standards.
This does not necessarily indicate
that higher temperatures were not achieved.
The incidence
of pathogens sought was negligible.
No salmonellae, C . per-
fringens, or coliforms were found.
Staphylococci were found
in negligible amounts.
Total counts were low which coincides
with the low incidences of other organisms.
The average
time that each dish was served does not seem to have any
importance as far as the total counts are concerned.
A
sampling period may have varied from 2.75 hours to 5 hours
but no increasing or decreasing trend was noted which would
distinguish these varying periods of time.
The particular
foods tested appear to be safe bacteriologically in spite
of the longer hours which the foods are maintained at serv­
ing temperatures.
75
Conclusions
From the data collected, the following conclusions
can be ascertained in response to the original hypotheses:
1.
Is there any evidence of C. perfringens, Salmon­
ella , or Staph, aureus in the casseroles examined in this
cafeteria?
The three casseroles tested in this cafeteria are
of excellent quality bacteriologically,relative
to the three organisms sought. Despite the
temperatures measured (which were generally below the
Public Health Standards), the foods tested were
definitely safe for consumption as far as the three
pathogens tested are concerned and within the limits
of the methods used.
2.
If there is evidence of contamination, would
proper heat treatment have eliminated the danger?
Although contamination was negligible, the tempera­
tures of the foods during cooking and holding were
generally below the Public Health Standards for
safety at the time of sampling. However, this does
not mean that the foods did not attain higher and
more satisfactory temperatures at some point in
their preparation.
3.
Are increased sanitation procedures needed to
insure greater consumer safety?
There is some indication that some improvement in
food handling practices of employees may be warranted.
The high counts in the pork chop suey cannot be
attributed to chance alone but should render some
concern for the danger which could accrue.
76
4.
Do the lengthened serving hours have implications
as far as food safety in this cafeteria is concerned?
The lengthened serving hours observed in this food
service seem to pose no threat to the safety of the
food served with respect to the three foods tested,
and especially if the sanitary practices are main­
tained at their current level.
Recommendations
If further related studies are made, the investigator
suggests a similar evaluatiom of various cream desserts and
salads maintained at room temperatures during a meal.
The
probability that such desserts and salads will be held for
serving at a later meal is more likely than for the casse­
roles tested in this study.
An evaluation of the food
handling procedures common in this cafeteria may be a good
source for the development of a viable teaching program.
This may include the employee attitudes toward such a
program if it were developed.
If further studies are done similar to the one
herein discussed, the researcher might consider the follow­
ing suggestions which may improve the results.
For heated
or similarly damaged cells, a more accurate recovery of
staphylococci may occur if a lower salt concentration
is used in the enrichment medium.
The commercial XLD used
77
here was found inferior in all aspects and it is recommended
that it be replaced for salmonellae isolation.
If equipment
is not limited, the experiment would be improved if micro­
biological data were available on raw products and on the
prepared foods after cooled.
In this way, the researcher
would have a broader comparative basis for determining food
quality in the service of concern.
78
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n
APPENDIX
57
Appendix A
Recipes
A-I
Tuna Noodle Casserole (600 servings):
60
13
33
6
2
1/2
1/4
2
pounds noodles
cans tuna
cans mushrooms
gallons plus I quart milk
cupps salt
cup pepper
cup onion salt .
cups parsley
Cook noodles in salt water until done. Mix all
other ingredients together and heat. Add noodles. Put
in pans and sprinkle with crumbs or cheese. Bake 45
. minutes at 350 F .
Yield: 25 pans, 30 servings/pan.
A-2
Pork Chop Suey (600 Servings):
6 gallons meat stock
4 1/2 cups salt
4 1/2 Tablespoons pepper
24 pounds sliced onions
48 pounds diced celery
4 pounds plus I Tablespoon cornstarch
12 Number 10 cans bean sprouts
12 cups soy sauce
54 pounds uncooked rice
150 pounds pork cubes
Brown meat. Cover. Simmer I hour. Add onions,
celery; continue cooking 30 minutes. Make paste of
.cornstarch and water from bean sprouts. Add to meat
and vegetables. Add bean sprouts and soy sauce.
Continue cooking until thickened. Serve on rice.
98
Appendix A
Recipes
A-3
Beef Stroganoff (600-650 servings):
6
12
I
6
100
12
200
20
15
cups prepared mustard
cups brown sugar
cup plus 3 tablespoons worchestershire sauce
gallons plus 2 pints sour cream
salt
pepper
onions— medium, thinly cut
pounds butter
pounds beef cubes
cans tomato soup
Number I cans mushrooms
Brown onions. Remove from fat. Brown meat, add
other ingredients. Cook until tender— I 1/2 hours.
- Serve over buttery poppy seed noodles or steamed rice
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