CHAPTER: 9
Dairy Microbiology
Ø Microbiology
of Milk and Milk Products
Ø Food-Borne
Infection
Ø Toxin
Ø Pasteurization
…………………………………………
Microbiology
of Milk & Milk Products:
• Milk is one of the best available complete foods
for man & it has high nutritive value.
• It
is enriched with various nutritional elements, so milk forms an excellent
medium for the growth & multiplication of several microorganism.
Sources
of Microorganisms in milk:
• Teat
openings of cows, buffaloes, are usually contaminated with microorganisms &
this is the primary source of microorganisms present in milk.
• Storage
utensils.
• Hands
of person who milks.
• Atmosphere
of milking place
• Body
surfaces of animals
• Utensils
used for milking
• In
machine- milking, the machine, pipelines, & the udders are the chief
sources of contamination.
Types
of Microorganisms encountered in Milk:
1. Normal
microflora, of most of the milk samples
2. Some
spoilage organisms which gain entry into milk through various sources.
3. Some
organisms which are pathogenic to man and animals
1.
Normal Microflora:
• Usually,
lactic acid producing bacteria are normal flora found in milk.
Examples:
• Lactobacillus
acidophilus, L. bulgaricus, L. bovis, L. fermenti, L. thermophilus,
Streptococcus cremoris, Leuconostoc citrovorum, Microbacterium lacticum,
Micrococus luteus.
Ø These
microorganisms ferments lactose of milk & produce acids, primarily lactic
acid.
2.
Spoilage Microorganisms:
• These
microorganisms spoil & degrade the quality of milk.
Examples:
• Coliforms
(E. coli, Klebsiella) ferment milk & produce gas.
• Clostridium
butyricum, Candida pseudotropicalis & Torulopsis produce
gas.
• Enterobacter
aerogenes, Micrococcus spp., Streptococcus spp.,
cause ‘ropy milk’. They cause the milk to become viscous or stringy, and
produce a gummy substance in the medium.
• Milk
is coagulated or curdled without acid production, when the casein content is
coagulated. This is brought by bacteria, e.g.: Bacillus subtilis, B. cereus,
Pseudomonas viscosa, and Streptococcus lignefaciens.
• Pseudomonas
fluorescens, Candida lipolytica, Penicillium spp. split the
fat in milk & produce glycerol & fatty acids.
3.
Pathogenic Microorganisms:
• Several
pathogenic microorganisms may spread through milk & cause disease
outbreaks.
Examples:
• Mycobacterium
tuberculosis, Coxiella burnettii, Bacillus, Clostridium, Salmonella, Shighella etc
Ø It is a good source of disease transmission .
Pathogenic organisms from infected cow may pass on milk and through milk to man
or calves.
Ø Tuberculosis,
brucellosis, typhoid, diphtheria, dysentery etc are some e.g. of disease
transmitted through milk.
The
organisms which attack milk can also be divided as;
1. Saccharolytic:
Those
organisms which degrade sacchrose (carbohydrates) & produce acid. E.g. Lactobacillus
spp., Streptococcus cremoris etc.
2. Lipolytic:
Those
organisms which degrade lipids. E.g. Micrococcus spp., Candida
lipolytica, etc
3. Proteolytic:
Those
organisms which degrade protein like casein. E.g. Bacillus subtilis,
Pseudomonas viscosa.
Microbiology
of Milk Products:
1. cheese:
• Cheese
is a dairy product formed by precipitating casein of milk in the form of curd,
holding most of fat & other suspended materials of milk.
• Different
kinds of microorganisms are involved in production of cheese
2.Fermented Milk:
• Fermented
milk is the most widely known dairy product. Souring of milk has been a common
practice followed since ancient times.
• The
microorganism involved in this process
are specific kinds of lactic acid bacteria (genera: Streptococcus and
Lactobacillus) which are allowed to develop and ferment the milk.
• In
non-commercial practices, the fermented milk can be obtained by inoculating the
milk with starters like , Streptococcus and Lactobacillus.
• There
are several organisms used on industrial scales to manufacture fermented milk
products. The organisms concerned are: Streptococcus lactis, S.
thermophilus, S. faecalis, Leuconostoc citrovorrum, L. cremoris, L. bulgaris,
L. acidophilus, etc.
Ø Yoghurt
is fermented milk ; the organisms involved in its production is Streptococcus
lactis and Lactobacillus bulgaricus.
Spoilage of Food:
• Spoilage is
the process in which food deteriorates to the point in which it is
not edible to humans or its quality of edibility becomes reduced. Various
external forces are responsible for the spoilage of food. Food that is capable
of spoiling is referred to as perishable food.
Causes of Food Spoilage:
1. Activity
of Microorganisms
2. Insect
damage
3. Purely
chemical damage
4. Physical
Change
Microbial Spoilage of various types of
Food Materials:
1. Grains:
• Large
quantities of foodgrains are damaged by insect pests which leads to greater losses due to microbial attack.
• High
moisture content , high atmospheric humidity, high moisture absorbing capacity
may lead to heavy damage by the microorganisms.
• Rhizopus
nigricans, Penicillum expansum, Aspergillus niger, & Mucor spp.
are the major moulds associated with grains spoilage.
• Bread
is more often attacked by R. nigricans.
• Bacillus
subtilis also attacks breads causing ropiness
• Serratia
marcescens when attacks to bread turns red due to
pigment produced by it.
2. Vegetables & Fruits:
• The
organisms which attack the vegetables and fruits may be: common plant pathogens
& saprophytic organisms.
• Soft-rots
of vegetables caused by bacteria are very common throughout the world.
• Erwinia
carotovora, E. aroideae, E. amylovora & Rhizopus spp.
cause soft-rots of vegetables and fruits.
• Several
fungi like penicillium, Cladosporium, Alternaria, are known to cause
damage to vegetables and fruits.
3. Meat and Meat Products:
• Meat
and meat products are exposed to various types of microbial contaminants.
• Pseudomonas
, Leuconostoc, Bacillus, Micrococcus, Flavobacterium, Chromobacterium are
some genera associated with meat spoilage.
• Fungi
like Penicillum Cladosporium,
Mucro, are also important in meat spoilage.
4. Fish and other sea foods:
• The
most common bacterial flora of water play a role in spoilage of fish and other
sea foods.
• Fish
spoilage is common due to Escherchia, proteus, Serratia, Sarcina etc.
• Canned
fish is spoiled by Clostridium and Bacillus.
5. Eggs:
• The
sources of microbial contaminants of eggs may be fecal matter of the hen, soil,
or water.
• These
may contaminate the shell and then penetrate it, if the shell is moistened or
cracked.
• More
commonly , Pseudomonas fluorescens and Proteus melanovogenes cause
green and black-rot spoilage of egg.
6. Spoilage of canned food:
• Bacillus
aerothermophillus, B. thermoindifferens, B. stearophilus, Clostridium
thermosacchrolyticum, C. nigrificans cause extensive
spoilage of canned food.
• The
spoilage may result from the attack of microorganisms which have survived
processing, or the organisms may gain access to the cans through defective
containers.
Prevention:
• A
number of methods of prevention can be used that can either totally prevent,
delay, or otherwise reduce food spoilage.
• Preservatives can
expand the shelf life of food and can lengthen the time long enough
for it to be harvested, processed, sold, and kept in the consumer's home for a
reasonable length of time.
• Refrigeration can
increase the shelf life of certain foods and beverages, though with most items,
it does not indefinitely expand it. Freezing can preserve food even longer,
though even freezing has limitations.
• A
high-quality vacuum flask (thermos) will keep coffee, soup, and other
boiling-hot foods above the danger zone (140F/58C) for over 24 hours.
• Canning of
food can preserve food for a particularly long period of time, whether canned
at home or commercially. Canned food is vacuum packed in order to
keep oxygen out of the can that is needed to allow bacteria to break it down.
Canning does have limitations, and does not preserve the food indefinitely.
• Lactic
acid fermentation also preserves food and prevents spoilage.
Food-borne Infection & Toxin:
• Foodborne
illness (also foodborne disease and
equally referred to as food poisoning) is any illness resulting
from the consumption of contaminated food, pathogenic bacteria, viruses,
or parasites that contaminate food, as well as chemical or
natural toxins such as poisonous
mushrooms.
Symptoms of Foodborne Illness:
• Common
symptoms of foodborne illness are diarrhea and/or vomiting, typically lasting 1
to 7 days. Other symptoms might include abdominal cramps, nausea, fever,
joint/back aches, and fatigue.
• “stomach
flu” may actually be a foodborne illness caused by a pathogen (i.e., virus,
bacteria, or parasite) in contaminated food or drink.
• The
incubation period (the time between exposure to the pathogen and onset of
symptoms) can range from several hours to 1 week.
Causes of Foodborne Illness:
Commonly recognized foodborne infections are:
• Campylobacteriosis
(Campylobacter)
• Cryptosporidiosi
(Cryptosporidium)
• Escherichia coliO157:H7Infection(E.coli O157)
and Hemolytic Uremic Syndrome (HUS)
and Hemolytic Uremic Syndrome (HUS)
• Giardiasis (Giardia)
• Norovirus
Infection (aka Norwalk virus, calicivirus, viral gastroenteritis)
• Salmonellosis
(Salmonella)
• Shigellosis
(Shigella)
• Yersiniosis
(Yersinia species)
Foods Associated with Foodborne Illness:
• Raw
foods of animal origin, that is, raw meat and poultry, raw eggs, unpasteurized
milk, and raw shellfish are the most likely to be contaminated.
• Fruits
and vegetables can also be contaminated with animal waste when manure is used
to fertilize produce in the field, or unclean water is used for washing the
produce.
• Unpasteurized
fruit juices can also be contaminated if there are pathogens on the fruit that
is used to make it.
• Any
food item that is touched by a person who is ill with vomiting or diarrhea, or
who has recently had such an illness, can become contaminated. When these food
items are not subsequently cooked (e.g., salads, cut fruit) they can pass the
illness to other people.
Some Common Food-borne Infections:
1. Salmonellosis:
• Salmonellosis is a form of food infection that
may result when foods containing Salmonella bacteria are consumed. Salmonella
enteritidis and Salmonella typhimurium are the most common.
• Once
eaten, the bacteria may continue to live and grow in the intestine, set up an
infection and cause illness.
• Symptoms of salmonellosis include headache,
diarrhea, abdominal pain, nausea, chills, fever and vomiting. These occur
within 8 to 72 hours after eating contaminated food and may last four to seven
days.
• Foods commonly involved include eggs or any
egg-based food, salads (such as tuna, chicken, or potato), poultry, beef, pork,
processed meats, meat pies, fish, cream desserts and fillings, sandwich
fillings, raw sprouts, and milk products.
2. Campylobacteriosis:
• Campylobacteriosis
or Campylobacter enteritis is caused by consuming food or water contaminated
with the bacteria Campylobacter jejuni. C. jejuni commonly is found in
the intestinal tracts of healthy animals (especially chickens) and in untreated
surface water. Raw and inadequately cooked foods of animal origin and
non-chlorinated water are the most common sources of human infection (e.g., raw
milk, undercooked chicken, raw hamburger, raw shellfish).
• Diarrhea,
nausea, abdominal cramps, muscle pain, headache and fever are common symptoms.
Onset usually occurs two to ten days after eating contaminated food.
• Preventive
measures for Campylobacter infections include pasteurizing milk; avoiding
post-pasteurization contamination; cooking raw meat, poultry and fish.
3. Listeriosis
:
• It
is caused by Listeria monocytogenes.
• Listeriosis
primarily affects newborn infants, pregnant women, the elderly and those with
compromised immune systems.
• In
a healthy non-pregnant person, listeriosis may occur as a mild illness with
fever, headaches, nausea and vomiting.
• Among
pregnant women, intrauterine or cervical infections may result in spontaneous
abortion or still birth.
• Recent
cases have involved raw milk, soft cheeses made with raw milk, and raw or
refrigerated ready-to-eat meat, poultry or fish products.
• Preventive
measures for listeriosis include maintaining good sanitation, turning over
refrigerated ready-to-eat foods quickly, pasteurizing milk, avoiding
post-pasteurization contamination, and cooking foods thoroughly.
4. Shigellosis:
• Shigellosis
is an illness caused by bacteria from the Shigella group. It is commonly known
as "bacillary dysentery".
• Symptoms
such as diarrhoea, fever, nausea, vomiting and cramps are most common. Blood
may also be found in the faeces.
5. Amoebiasis:
• Amoebiasis
is an intestinal disease caused by the parasite Entamoeba histolytica.
• The
disease is commonly known as "amoebic dysentery" and results when the
parasite invades the wall of the large intestine, forming ulcers in the
process.
• Symptoms
such as diarrhoea, fever, chills, and mild abdominal discomfort are the most
common.
6. Giardiasis:
• Giardiasis
is an intestinal disease caused by the parasite Giardia lamblia.
• Symptoms
such as diarrhoea, abdominal cramps, bloating, fatigue and weight loss may
occur.
7. E.
coli Hemorrhagic Colitis:
• It
is caused by E. coli O157:H7.
• Symptoms
begin with nonbloody diarrhea one to five days after eating contaminated food,
and progress to bloody diarrhea, severe abdominal pain and moderate
dehydration. In young children, hemolytic uremic syndrome (HUS) is a serious
complication that can lead to renal failure and death. In adults, the
complications sometimes lead to thrombocytopenic purpura (TPP), characterized
by cerebral nervous system deterioration, seizures and strokes.
• Ground
beef is the food most associated with E. coli O157:H7 outbreaks, but other
foods also have been implicated. These include raw milk, unpasteurized apple
juice and cider, dry-cured salami, homemade venison jerky, spinach, and untreated water. Infected food
handlers and diapered infants with the disease likely help spread the bacteria.
• Preventive
strategies for E. coli infections include thorough washing and other measures
to reduce the presence of the microorganism on raw food, thorough cooking of
raw animal products, and avoiding recontamination of cooked meat with raw meat.
To be safe, cook ground meats to 1600 F.
Food intoxication:
• Food
intoxication results from consumption of toxins (or poisons) produced in food
by bacterial growth.
• Toxins,
not bacteria, cause illness. Toxins may not alter the appearance, odor or
flavor of food.
• Common
kinds of bacteria that produce toxins include Staphylococcus aureus and
Clostridium botulinum. In the case of
Clostridium perfringens, illness is caused by toxins released in the gut when
large numbers of vegetative cells are eaten.
Some Bacterial Intoxication:
1. Bacillus
Cereus – Foodborne Intoxication:
• Bacteria
produce a toxin that causes illness. Vomiting-type outbreaks have usually been
associated with rice products and other starchy foods such as potatoes, pasta,
and cheese products. Sauces, puddings, soups, casseroles, pastries, and salads
have also been implicated in outbreaks.
• nausea
,vomiting , abdominal cramps and diarrhea might occur with symptoms lasting up
to 24 hours.
2.
Staphylococcal Intoxication :
• Staphylococcus bacteria are found on
the skin and in the nose and throat of most people; people with colds and sinus
infections are often carriers. Infected wounds, pimples, boils and acne are
generally rich sources. Staphylococcus also are widespread in untreated water,
raw milk and sewage.
• When
Staphylococcus bacteria get into warm food and multiply, they produce a toxin
or poison that causes illness. The toxin is not detectable by taste or smell.
While the bacteria itself can be killed by temperatures of 120 F, its toxin is
heat resistant.
• Foods
commonly involved in staphylococcal intoxication include processed meats,
chicken, sandwich fillings, cream fillings, potato and meat salads, milk
products
• Symptoms
include abdominal cramps, vomiting, severe diarrhea and exhaustion. These
usually appear within one to eight hours after eating staph-infected food and
last one or two days.
3. Botulism- Clostridium botulinum:
• Widely
distributed in nature; soil and water on plants and intestinal tracts of
animals and fish. Grows only in little or no oxygen.
• Bacteria
produce a toxin that causes illness. Improperly canned foods, garlic in oil,
vacuum-packed and tightly wrapped food.
• Toxins
affect the nervous system. Symptoms usually appear in 18 to 36 hours, but can
sometimes appear as few as four hours or as many as eight days after eating.
Double vision, droopy eyelids, trouble speaking and swallowing, and difficulty
breathing may occur.
4. Clostridium perfringens:
• The
disease produced by C. perfringens is not as severe as botulism.
• Spores
of some strains are so heat resistant that they survive boiling for four or
more hours.
• Foods commonly involved in C. perfringens
illness include cooked, cooled, or reheated meats, poultry, stews, meat pies,
casseroles, and gravies.
• Symptoms
occur within eight to 24 hours after contaminated food is eaten. They include
acute abdominal pain and diarrhea. Nausea, vomiting and fever are less common.
Mycotoxins and alimentary mycotoxicoses:
• The
term alimentary mycotoxicoses refers to the effect of
poisoning by Mycotoxins (The term 'mycotoxin' is usually reserved for
the toxic chemical products produced by fungi that readily colonize crops)
through food consumption.
• Mycotoxins sometimes
have important effects on human and animal health.
• The common foodborne Mycotoxins include:
Aflatoxins –
• They
are frequently found in tree nuts, peanuts, maize, sorghum and other oilseeds,
including corn and cottonseeds.
• The
pronounced forms of Aflatoxins are those of B1, B2, G1, and G2,
amongst which Aflatoxin B1 predominantly targets the liver, which will result
in necrosis,cirrhosis, and carcinoma.
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