CONTAMINATION, PRESERVATION AND SPOILAGE OF MILK AND

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CONTAMINATION, PRESERVATION & SPOILAGE
OF MILK AND MILK PRODUCTS
INTRODUCTION
Milk products include milk, cream, butter, frozen
deserts, cheese, fermented milks, condensed & dried
milk products.
 The nutritional qualities of milk & milk products
make the desirable foods for humans and young
animals.
 Milk is a product of animal origin, & its sanitary
qualities are influenced by many factors in the course
of its production, processing & delivery to the
consumer.
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CONTAMINATION
Contamination of milk occurs from various sources
which are:1.
CONTAMINATION FROM THE COW:Cow is the main source to give milk, which contains
relatively few bacteria, when it leaves the udder of a
healthy cow & generally these bacteria do not grow
under usual conditions of handling.
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Under unusual conditions milk is subjected to
contamination from the cow. That is:
A. THE INTERIOR OF THE UDDER
The bacteria present in the udder, enter at the teat
opening & are distributed internally by their own
growth as well as physically movement. Then they are
mechanically flushed out during milking.
 During progress of milking bacteria are present in the
largest numbers at the beginning & gradually decrease
because of the mechanically dislodgement of the
bacteria, particularly in the teat canal where their
numbers are probably highest.
 From the normal udders: In aseptically drawn milk, 100-10,000 per ml counts
have been reported.
 The anticipated average is probably between 500-1000
per ml.
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The bacteria which comes from the udder are: The micrococci:- generally present in greatest portion.
Many of these bacteria are comparatively slow growing,
but if allowed to grow cause proteolysis & acid
formation, resulting in a very distasteful product.
 The streptococci & rods:- occurs less frequently then the
micrococcus .
 The infected cows passed their pathogens throughout
the milk to cause infections in humans.
 These disease of cows are:- Mastitis, Brucellosis, Bouine
tuberculosis, Q fever.
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B. THE EXTERIOR OF THE UDDER
Udder gets contact with soil, manure, bedding, water
which increase the microbial load. Therefore good
sanitation conditions has to be applied to prevent the
entrance of many types of bacteria during milking
operation.
 Cleaning is done by wiping the udder with a disinfectant
solution.
 Quaternary ammonium compounds are more effective
sanitizer then chlorine for the udder & also less harmful.
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C. THE COAT OF THE COW
Coat of the cow may serve as a vehicle of contamination,
by adding bacteria directly to the milk during milking.
 The cows coat may carry bacteria from soil, manure,
stagnant pools of water.
 The bacillus organisms causing ropy milk.
 coliform bacteria comes in presence of soil, manure &
water.
 Therefore, daily brushing & cleaning of cow decrease
bacterial load.
 To Avoid bacteria clipping of the coat should be done,
including thighs, flanks, udder & tail.
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2. COMTAMIANATION FROM MILKING
UTENCILS
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Various utensils used for milking & handling are the most important
sources to gain bacteria in the milk.
In mechanical milking ,the increase use of equipments, such as
milking machines, permanent pipelines, & farm storage tanks
preventing exposure of the milk to dust, insects, & external sources of
contamination.
The material used for equipment should be well cleaned and
sanitized to avoid internal contamination.
the equipment should be of stainless steal or aluminum.
The equipments don’t have scratches because they collect milk
residues.
For cleaning the equipment these points should be kept in mind:Bacteria should be physically removed from utensils, residual milk
should be completely eliminated.
Equipment should be stored under dry conditions to prevent growth.
Before the use of equipment, bacteria should be killed by applying of
heat or chemical germicidal.
3. CONTAMINATION FROM MISCELLANEOUS
SOURCES
Organisms occur in air, varying in numbers & present
in a dormant condition.
 The number of these bacteria are relatively low
 the types of micro organisms normally present in air
are:- sporeformers, micrococci, & mold spores.
 The air may be expected to add, during hand
milking, 5-15bac\ml of milk.
 Continuous raising of dust can also add hundreds of
bac\ml of milk.
 Dust particles originating from manure, soil, & feed
may contain bacteria.
 Milking machines may contain lesser bacteria from
the air
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CONTROL MEASURES TO AVOID
CONTAMINATION
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FOR MECHANICAL MILKING:- Before use, the milking
machines & equipments should be well cleaned & sanitized.
Adequate light is needed to perform milking & cleaning
operations.
Proper ventilation is needed in a milk house, to avoid
condensation of moisture on the walls.
flies & insects must be kept out to avoid pathogens &
bacterial load.
Cow yards & loose housing areas should be adequately
drained & manure should be removed frequently.
FOR HAND MILKING:- Hands must be free from any
infections, cuts, wounds because infected hands can add
pathogenic streptococci, micrococci to milk & cause
subsequent human infection.
Wet hand milking should be avoidable because it add bacteria
from hands to teats.
MECHANICAL MILKING
PRESERVATION
Milk is such a delicately flavored, easily changed food. So the
prevention of contamination or spoilage of milk is important
in its preservation.
 Most of the milk products evolved for the purpose of
improving keeping quality.
 Keeping quality is usually increased when smaller no. of
organisms are present. Normally lower the microbial load
better the keeping quality.
 To increase the keeping quality of milk one should have to
decrease the no. of undesirable kinds of micro-organisms : These undesirable organisms are:1. lactis & coliforms:- they grow well in market milk.
2. the psychrotrophs:- grow well at refrigeration temperature in
stored milk.
3.the thermodurics:- which survive pasteurization i.e human
pathogens
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METHODS OF PRESERVATION
1.REMOVAL OF MICRO-ORGANISMS
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Once organisms have enter to milk, it is difficult to
remove them effectively.
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Centrifugation process is done to as in seperating,
will remove some organisms from milk.
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This process is also known as bactofugation.
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High speed centrifugation removes (atleast 10,000)
99 % of the spores & more than half of the
vegetative cells of bacteria plus some protein.
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This process is not used extensively on a
commercial basis.
2. USE OF HEAT
a. PASTEURIZATION
Pasteurization is done with 2 methods:1. LOW TEMPERATURE HOLDING METHOD:- the process of
heating every particle of milk or milk products to atleast 63
degree C., and holding at such temperature continuously for
atleast 30 min.
2. HIGH TEMPERATURE, SHORT TIME:- when milk is pasteurized at
72 degree C.., for 15 sec followed by the quick cooling.
OBJECTIVES OF PASTEURIZATION:a. To destroy pathogenic organisms which may present in milk.
b. To enhance the keeping quality of milk & milk products.
c. To destroy organisms that would interfere with the desirable
organisms such as starter culture.
B.
STEAM UNDER PRESSURE
Evaporated milk is canned & then heat processed by
steam under pressure, often with accompanying
rolling.
 The fore-warming of milk at about 93 to 100 C or
higher, to kill all or more resistant bacterial spores.
 Sealed canes of evaporated milk are processed at
about 115-118 C for 14-18 min, which results in a
commercially sterile product.
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3. USE OF LOW TEMPERATURES
Most dairy products require the use of low temperatures,
except canned milk & dry milk.
a. REFRIGERATED STORAGE: For the production of milk of good quality it is essential to
cooling the milk after it withdrawn from cow.
 Grade A raw milk for pasteurization shall be cooled 1
degree C or less within 2 hours after being drawn & kept
that cold until processed.
 Newly pasteurized milk is to be cooled to 7.2 C or less.
 Milk is held at refrigeration temperature during storage on
the farm, in the truck or tank during transportation to the
receiving station.
 Fermented milks & unripened (or ripened cheese to store)
are chilled after their manufacture & kept chilled until
they reach the consumer.
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B. FREEZING
Ice cream, & other frozen dairy deserts are frozen as a
part of manufacturing process.
 It also stored at low temperatures in the frozen state,
where microbial multiplication is impossible.
 Freezing kills relatively few of the bacteria & storage
in the frozen state permits survival of most of the
organisms for long period.
 Butter in storage is held at -17 to -18 or lower, where
no microbial growth occur.
 Pasteurized whole milk has been frozen at about -28
to -29 C & stored at frozen state.
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4. DRYING
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Dry products are made by removing different percentage
of water from whole milk & skim milk.
Enough moisture is removed to prevent the growth of
organisms.
CONDENSED PRODUCTS:Evaporated milk is made by removing about 60% of the
water from whole milk, so about 11.5% lactose would be
in solution plus twice the organic salts. This high
concentration of sugar is inhibit the growth of bacteria.
Bulk condensed milk is more evaporated milk & due to
this organisms doesn’t tolerant of high sugar
concentration.
So these products is of good keeping quality.
b. DRY PRODUCTS:•
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Dry products are prepared from milk, skim milk, cream,
whey, buttermilk, ice-cream mix, & malted milk.
Most dry milk is prepared by roller process, with or
without vacuum or by spray process.
Preliminary to final drying process milk is concentrated
5 times for the roller process & 2-3 times for the spray
process.
Usually milk is preheated before drying . This preheating
process pasteurizes the milk& kills less heat-resistant
bacteria.
The high temperature of the roller process without
vacuum destroy almost all organisms except spores.
5. USE OF PRESERVATIVES
1.
ADDED PRESERVATIVES:-
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Sorbic & propionic acid or their salts is permitted in
cottage cheese, yogurt, to prevent growth of molds on
their surface & increase their shell life
They also added in some of the hard cheeses &
processed cheeses to prevent the surface growth of
molds.
Added sugar acts as a preservative of sweetened
condensed milk; & making moisture unavailable to
organisms.
The sodium chloride in salted butter decrease the
number of those who are not salt tolerant.
Addition of hydrogen peroxide combined with a mild
heat treatment has been used for pasteurization of milk
for destroy certain kinds of bacteria.
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B. DEVELOPED PRESERVATIVES
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Most fermented products are micro-biologically more stable or
have longer shell life than the initial substrate.
Fermented milks & cheese are preserved partly by the developed
acidity produced by bacterial culture.
Therefore they have longer shall life than the fluid milk.
6. OTHER METHODS:Preservation can be done by :a. Pasteurization of the milk with ultra-violet treatment.
b. Evaporated milk is processed by steam under pressure to kill
organisms & sealed in canes to keep out contamination.
c. Sweetened condensed milk undergoes a pasteurization during
its preparation, contains a high concentration of sugars,& is
protected by sealed can.
SPOILAGE
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Milk & milk products have limited keeping time & after that they spoil readily.
Spoilage may also occur, if the methods of preservation are inadequate.
1. .SPOILAGE OF RAW MILK:
Because of the fermentable sugar(lactose) present in milk, an acid formation by
bacteria occurs in raw milk.
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Acid formation cause 1st sour flavor of milk, then coagulation of milk gives solid
jellylike curd or a weaker curd that releases clear whey.
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Lactic acid fermentation takes place in raw milk at room temperature.
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In raw milk at temperature from 10-37 C, Streptococcus lactis cause the souring,
with possibly some growth of coliform bacteria, enterococci, lactobacilli,&
micrococci.
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At higher temperature, from 37-50 C, S thermophillus may produce 1% acid & to
be followed by lactobacilli, such as Lactobacillus bulgaricus which will produce
more acid.
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Some of lactobacilli can grow at still higher temperature above 50 C but produce
less acid.
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Little formation of acid occurs at temperature near freezing.
2. SPOILAGE OF PASTEURIZED MILK: Pasteurization of milk kills the more active acid forming
bacteria but permit the survival of heat resistant lactis
which cause lactic acid fermentation.
E.g. Enterococci,.
 Coliform bacteria produce some lactic acid Streptococcus
thermophillus, lactobacilli& some amounts of volatile
products.
Such as H, CO2, acetic acid, formic acid, alcohol, etc.
 Species of Micrococcus, Microbacterium, & Bacillus can
produce acid in milk.
 Butyric acid may be produced in milk by Clostridium under
conditions that inhibit the normal lactic acid formation.
 Clostridium spores survive even after the heat treatment ..
 so milk may undergo butyric acid fermentation with the
production of H, CO2.
3. GAS PRODUCTION
Gas production is usually accompanied by acid formation.
 The chief gas formers are:Clostridium, gas forming bacillus species- yield H & CO2.
The yeast, propionics & hetero-fermentative lactisproduce only CO2.
 The production of gas in milk is evidenced by:Foam at the top of liquid milk, gas bubbles caught in the
curd, by floating curd containing gas bubbles, by a ripping
of the curd by rapid gas production , causing stormy
fermentation of milk.
 Milk heated at pasteurizing temperature or above :the chief acid formers will be killed,
the spores of Clostridium & Bacillus species will survive,
and gas formation by the spore formers may take place.
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4. PROTEOLYSIS
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The hydrolysis of milk proteins by organisms is produced
bitter flavor in taste due to some of the peptides released.
Actively proteolytic bacteria found in the species of :Micrococus, Pseudomonas, Flavobacterium..
…they are from genera of non spore forming bacteria
Bacillus, Clostidiriium are genera of sporeformers.
Proteolysis is favored by: storage at a low temperature,
 by the destruction of lactis & other acid formers by heat,
 By the destruction of formed acid in milk by molds &
yeasts
 The neutralization of acids by products of other
organisms.
The types of change produced by organisms include:1. Acid proteolysis:- in this acid production &
proteolysis occur together.
Acid proteolysis causes the production of a shrunken
curd & it caused by several species of Micrococcus.
Proteolysis with little acidity or even with alkalinety,
2. Sweet curdling:- caused by the reninlike enzymes of
the bacteria(at early stage),
Slow proteolysis by intracellular enzymes of the
bacteria
3. Residual proteolytic activity of heat stable proteinase
for example pseudomonas fluorescens produces a
proteinase that will survive pasteurization.
Some species of Baciilus can survive pasteurization
5. ROPINESS
Ropiness can occur mostly in market milk & cream.
 Bacterial ropiness caused by slimy capsular material from
the cells, usually gums or mucins & develops best at low
temperatures.
 The ropiness usually decrease, as the acidity of the milk &
cream increases
 There are 2 main type of bacterial ropiness:1. one in which milk is most ropy at the top, and most
oftenly caused by Alcaligenes viscolactis.
2. the other in which milk is ropy throughout Which is
caused by numbers of bacteria.
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Ropiness is caused by Enterobacter usually is worse near
the top of the milk.
 Sources of the bacteria causing ropiness are:- water,
manure, utensils & feed.
 For prevent the ropiness, adequate pasteurization of milk
kills all kinds of bacteria.
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6. CHANGES IN MILK FAT
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Milk fat may be decomposed by various bacteria, yeasts, &
molds.
Changes occur in milk fat are:1.
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Oxidation of the unsaturated fatty acids:- yields
aldehydes, acids, ketones & results in tallowy odors &
taste.
Hydrolysis of the butterfat to fatty acids & glycerol by the
enzyme lipase.
Combined oxidation & hydrolysis to produce rancidity.
Species of lipase forming bacteria are found in :Pseudomonas, Alcaligenes, Bacillus, Micrococcus,
Clostridium etc.
7. ALKALI PRODUCTION
Alkali formers are:- Pseudomonas fluorescens & A.
viscolactis.
 The group of alkali formers cause alkaline reaction in
milk without any evidence of proteolysis.
 This reaction may result from the formation of
ammonia, as from urea, as from organic seeds(citric
acid).
 Most of these bacteria grow from moderate to low
temperatures, & many can survive pasteurization.
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8. FLAVOR CHANGES
OFF FLAVORS CAUSED BY MICRO-ORGANISMS ARE:1.
SOUR OR ACID FLAVOR:- when lactic streptococci &
aroma-forming Leuconostoc species are growing
together cause sharp undesirable flavors.
2.
BITTER FLAVORS:- Bitterness usually results from
proteolysis, fermentation of lactose, lipolysis. Some
cocci cause very bitter milk.
3.
BURNT OR CARAMAL FLAVOR:- resembles the cooked
flavor or over heated by Streptococcus lactis.
4.
MISCELLANEOUS FLAVOR:
A turnip like flavor by Eschrichia
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Fruity flavor by P. fragi
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A potato like flavor by P. mucidolens.
9. COLOUR CHANGES
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The color of milk or cream is affected by its physical &
chemical composition.
Color changes caused by micro-organisms may occur along
with other changes .
The color may be due to the surface growth of pigmented
bacteria in the form of a scump or ring or may be presented
throughout the milk.
BLUE MILK:- an acid former Streptococcus lactis causes a
deep blue color in milk culture.
YELLOW MILK:- Species of Flavobacterium can causes
yellowness.
RED MILK:- Micrococcus roseus may produce a red
sediment,
Yeast may produce red or pink colonies on the surface of
sour milk
BROWN MILK:- result from Pseudomonas putrifaciens.
10. SPOILAGE OF MILK AT DIFFERENT
TEMPERATURES
1. Spoilage of Raw milk at refrigeration temperature:
Proteolysis may be initiated by psychrotrophic bacteria
such as pseudomonas, & molds then appear.
 At room temperature, an acid fermentation is most
probable, 1st by lactic, streptococci, & coliform bacteria &
then by acid tolerant lactobacilli.
 Eventually when most of the acid has been destroyed,
proteolytic bacteria complete decomposition.
2. Spoilage of pasteurized milk is depend upon: The bacteria that survive pasteurization .i.e. “thermodurics”
& spore-formers.
 The bacteria that enter the milk following pasteurization
process to packaging process.
 Possible presence of heat resistant residual microbial
enzymes.
CONTAMINATION, PRESERVATION, SPOILAGE
OF MEAT & MEAT PRODUCTS
CONTAMINATION
The healthy inner flesh of meats have been reported to
contain few or no organisms,.
 Although they have been found in lymph nodes, bone
marrow, & even flesh.
 Staphylococci, streptococci, Clostridium, & Salmonella
have been isolated from the lymph nodes of red meat
animals.
 So normal slaughtering practices would remove the
lymph nodes from edible parts.
 Approved “humane” methods of slaughtermechanical, chemical, electrical- have little effect of
contamination..
 But each method is followed by sticking & bleeding,
which can introduce contamination.
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• The important contamination comes from external sources
during bleeding, handling & processing.
Sources of contamination may be:• Knives, cloths, air, & clothing of workers.
• During handling of meat, boxes, containers, air, & other
contaminated meat.
• During bleeding, skinning & cutting main source of
micro-organisms are the exterior of the animal & intestinal
tract.
• In the market, knives, saws, cleavers, slicers, grinders,
chopping blocks, scales & containers.
• In Home refrigerators previously used containers used to
store meat.
• Growth of organisms on surface, touching the meats & on
the meat themselves increases their numbers.
IMPORTANT ISOLATED MICRO-ORGANISMS FROM MEAT
PRODUCT
MICRO-ORGANISMS ISOLATED
FRESH &
REFRIGERATED
MEAT
BACTERIA:Pseudomonas, Aeromonas, Micrococcus, & Alcaligenes
MOLDS:Cladosporium, Geotrichum, & Mucor
YEASTS:Candida, Torulopsis, & Rhodotorula
PRECESSED & CURED BACTERIA:MEATS
Lactobacillus & other lactic acid bacteria, Bacillus.
Micrococcus, & Staphylococcus
MOLDS:Pencillium, Aspergillus, Rhizpus
YEASTS:Candida, Torula, Torulopsis
PRESERVATION
Meat is the most perishable food.
 Preservation of meats are more difficult than other foods.
 So the preservation of meats is done by combination of
preservative methods.
 Keeping organisms away from meat, during slaughtering &
handling, permits easier preservation by any method.
 Water spraying to the animal before slaughter has been
preferred to remove as much as gross dirt.
 Meat & meat products are preserved by following eight
methods…
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1. USE OF HEAT
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The canning of meat is very specialized technique – in that the
procedure varies with the meat product to be preserved.
Chemical added to meats, such as, spices, salts, or nitrates in
curing processes, also affect the heat processing, & make it more
effective.
Nitrates in meat helps to kill spores of anaerobic bacteria by heat
& inhibit germination of surviving spores.
Commercially canned meats can be divided into 2 categories:Meats that are heat processed to make the can contents sterile
or “commercially sterile” as for canned meats for shelf storage in
retail stores .
This meat group is also referred as “ shelf stable canned meats”.
The Processing temperature of this canned cured meats is 98 C.
Size of the container is less than 1 lb.
2.
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Meats that are heated enough to kill part of the spoilage microorganisms but must be kept refrigerated to prevent spoil.
This meat group is called as non-shelf stable or “ keep refrigerated”
canned meats.
They are packed in containers upto 22 lb.
Processed at temperatures of about 65 C.
HEAT MAY ALSO BE APPLIED IN OTHER WAYS THEN CANNING: Hot water can be used for treatment of meat surfaces to lengthen the
keeping time of meat..
 But this may lessen the nutrients & damage color.
 Hot water reduces the numbers of organisms & helps preservation.
 Heat applied during the smoking of meats & its products helps to
reduce microbial numbers
 Cooked sausages such as frankfurters & liver sausage, also be spiced
but should be kept refrigerated.
2. USE OF LOW TEMPERATURES
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More meat is preserved by the use of low temperatures, 1st chilling &
then by freezing method.
1. CHILLING
 Modern packing house methods involve chilling meat immedieately &
rapidly to temperature near freezing
 Chilling storage at only slightly above the freezing point.
 The more prompt & rapid this cooling, cause less growth of mesophillic
organisms.
 Storage temperature vary from -1.4 to 2.2 C, with the lower temperature
preferred.
 Time limit of chilling is depending upon microbial load & vary
according to animal:For beef, is about 30 days , for pork, lamb & mutton is 1-2 weeks, for a
veal, needs short period.
 Uncooked sausage must be preserved by refrigeration.
 Storage time can be increased by 2.5 to 3 ppm ozone in the atmosphere.
 Ozone is an active oxidizing agent, that may give an oxidized or tallowy
flavor to fats.
2. FREEZING
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Freezing often is used to preserve meats:during shipment over long distances,
for holding until times of shortage,
quantities of meat now are frozen in home freezers.
The preservation of frozen meats is increasingly effective as the
storage temperature drops from -12.2 to -28.9 C.
The freezing process kills about half the bacteria..
And numbers decrease slowly during storage.
The low temperature bacteria that grow on meat during chilling
:That is from species of Pseudomonas, Alcaligenes, Micrococcus,
Lactobacillus, Flavobaterium , & can resume growth during the
thawing of meat after this is done.
3. USE OF IRRADIATION
Irradiation with UV rays has been in conjunction
with chilling storage to lengthen the keeping time.
 The rays serve:to reduce numbers of organisms in the air &
to inhibit or kill them on the surface of the meat.
 Irradiation has been used in the rapid aging of meats,
that are ‘hung’ at higher than the usual chilling
temperatures to reduce the growth of organisms on
the surface.
 Gamma irradiation of meats still is limited & in the
experimental stage.
 Because it cause undesirable changes in flavor &
color.
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4. PRESERVATION BY DRYING
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Meat for drying should be of good bacteriological quality to
avoid undesirable flavor.
Meat products, such as dry sausages & dry cervelats are
preserved by their low moisture content & dryness.
Dried beef made mostly from cured, smoked beef hams,
growth of organisms may takes place before processing..
And may develop in the ‘pickle’ during curing..
But Numbers of organisms are reduced by the smoking & drying
process.
Drying may be by vaccum, in trays.
Drying pork involves a short nitrate-nitrite cure before drying &
addition of lecithin as an oxidant & stablizer…
The final product keeps without refrigeration.
Freeze drying processed products include.. Meat patties, meat
balls etc.
5. USE OF PRSERVATIVES
Use of preservatives is combined with curing & smoking in order to be
affected.
1. CURING:The curing of meats is limited to beef & pork.
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The curing agents permitted are:sodium chloride, sugar, & nitrate are commonly used, vinegar is less
useable.
Functions of the agents are:
Sodium chloride- used as a preservative & flavoring agent. Its main
purpose is to lower Aw.
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Sugar adds flavor & serves as an energy source for nitrate-reducing
bacteria in the curing solution. Sucrose is chiefly used , glucose
used as a subsituted.
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Nitrate used as a color fixative & has some bacteriostatic effect in
acid solution.
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Sodium chloride attributed most preservative effects of the curing
agent.
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Salts, Sugars, & meat protein combine to lower the Aw value of the
cured meats.
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There are 4 methods for introducing curing agents into meat:1.
2.
3.
4.
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The dry curedry ingredients are rubbed into the meat.
The pickle curethe meats are immersed into a solution of the ingredients.
The injection curea concentrated solution of the ingredients is injected by needle
into arteries of the meat.
The direct addition methodthe curing agents are added directly to finely ground meats.
The curing temperature usually is about 2.2 to 3.3 C.
And the time of the cure varies with the method used.
The older method of curing in the pickle require several
months..
Where as the newer ‘quick cure’ in which pickling solution is
pumped into the meat, greatly shortens the time.
6. SMOKING:1.
2.
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Smoking has two main purposes:To add desired flavors.
To aid in preservation.
Preservative substances added to the meat, together with the
action of the heat during smoking, have a germicidal effect.
Drying of the meat, together with chemicals from the smoke,
inhibits microbial growth during storage.
SPICES:Spices and condiments added to meat products to add their
effect to other preservative factors.
For example – bologna, polish, & frankfurter & other sausages
owe their keeping quality to the combined effect of spicing,
curing , smoking, cooking, & refrigerating.
8. ANTIBIOTICS
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Antibiotics can be used successfully in meats to prolong
storage life at chilling or high temperature.
The most often recommended antibiotics are:chlortetracycline & chloramphenicol.
The antibiotics may be applied to meats in various methodsThe antibiotic may be fed to the animal over a long period.
It may be fed to more intensively for a short period before
slaughter,
It may be infused into the carcass or its part of it.
It may be applied to the surface of pieces of meat or mixed
with continued meat.
Antibiotic injection before slaughter might be employed to
prolong the keeping time of carcasses at atmospheric
temperature before they reach the refrigerator.
The storage life of meats could be lengthened by the means
of antibiotics.
SPOILAGE
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Raw meat is subjected to change by its own enzymes & by microbial
action & its fat may be oxidized chemically.
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All kind of microorganisms which cause spoilage
can grow under favourable conditions...
1. Invasion of tissues by microorganisms:- upon the death, invasion of
the tissues by contaminating micro-organisms takes place.
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Factors that influence the invasion include:a.
The load of gut of the animal- more the load, greater the invasion
of tissues.
b.
The physiological condition of the animal immediately before
slaughter- if the animal is excited, feverish bacteria is more likely
to be enter the tissues.
c.
The method of killing & bleeding- the better sanitary the
bleeding, better would be the keeping quality of meat.
d.
The rate of cooling- rapid cooling will reduce the rate of invasion
of tissues
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Factors that influence the growth of microorganisms to cause
spoilage are as..
The kind and amount of contamination with microorganisms &
the spread of these organisms in the meat.
The physical properties of meatThe amount of exposed surface of the flesh influence on the rate
of spoilage.
The chemical properties of meatThe moisture content of the meat determine organisms to grow.
Availability of oxygenAerobic conditions at the surface of meat are favorable to yeasts,
molds & aerobic bacteria.
TemperatureLow-temperature organisms can grow on stored temperature of
meat i.e. not far above freezing.
GENERAL TYPES OF SPOILAGE OF MEAT
SPOILAGE UNDER AEROBIC CONDITIONS:1. Surface slime
which may be caused by species Pseudomonas, Leuconostoc,
Bacillus etc.
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Temperature & availability of moisture, influence the kind of
organisms causing surface slime.
2. Changes in color of meat pigments
The production of oxidizing agents causes change in red color
of meat to shades of green, brown & gray, by bacteria species of
Lactobacillus.
3. Changes in fats
The oxidation of unsaturated fats in meats takes place
chemically in air & may be catalyzed by light & copper.
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Lipolytic bacteria may cause lipolysis.
4. Phosphorescence
Uncommon defect caused by luminous bacteria.
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Example. Photobacterium , growing on the surface of meat.
5. Various surface color due to pigmented bacteria
E.g. Yellow discoloration may be cause by bacteria with yellow
pigment i.e. species of Micrococcus or other.
6. Off odors and off tastes
undesirable tastes & odors, appear in meat due to growth of
bacteria on the surface often are evident before other signs of
spoilage.
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Souring is term applied to almost any defect, that gives a sour
odor may be due to volatile acid.
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Under Aerobic conditions, yeast grow on the surface of meats,
causing.. Sliminess, lipolysis, off odors, & tastes, and
discolorations.
Aerobic growth of molds may cause., stickiness,
whiskers (white fuzzy growth), black spot,
Green patches, decomposition of fats, off odors & tastes.
SPOILAGE UNDER ANAEROBIC CONDITIONS
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Facultative and anaerobeic bacteria are able to grow within the meat
under anaerobic conditions to cause spoilage.
The terminology used in connection with this spoilage is:SOURING:The term implies a sour odor.
This could be caused by formic, acetic, byutric, propionic and
higher fatty acids or other organic acid like lactic.
Vacuum packed meats, especially those in gastight wrappers,
commonly support the growth of lactic acid bacteria.
Souring can result fromAction of meat own enzymes during ripening
Anaerobic production of fatty acids or lactic acid during ripening.
Proteolysis without putrefacation, caused by anaerobes.
2. PUTREFACTION: True putrefaction is the anaerobic decomposition of
protein with the production of foul smelling compounds.
 It usually is caused by species of Clostridium.
 But facultative bacteria may cause putrefaction in its
production, by species of putrfaciens, putrificum..etc..,
chiefly in the genera Pseudomonas and Alcaligenes.
 Gas formation accompanies putrefaction by clostridia, the
gases being hydrogen & CO2.
3. TAINT:
This word is implied to any off-taste, off-odor.
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The term ‘bone taint’ is implied to souring or
putrefaction.
SPOILAGE IS ALSO INFLUENCED BY
TEMPERATURE
Not only air but temperature has an important
influence on the type of spoilage to be expected in
meat.
 When meat is held at temp. near 0 C, microbial
growth is limited to molds, yeasts, & bacteria able to
grow at low temperatures.
 This include:- sliminess, discoloration and spots of
growth on the surface.
 Many bacteria can cause souring.. Such as
Pseudomonas, Lactobacillus, Leuconostoc,
Streptococcus.. etc.
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