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.

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.

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.

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.

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.

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.

2. COMTAMIANATION FROM MILKING UTENCILS

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

CONTROL MEASURES TO AVOID CONTAMINATION

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

METHODS OF PRESERVATION

1.REMOVAL OF MICRO-ORGANISMS Once organisms have enter to milk, it is

difficult to remove them effectively. Centrifugation process is done to as in

seperating, will remove some organisms from milk.

This process is also known as bactofugation. High speed centrifugation removes (atleast

10,000) 99 % of the spores & more than half of the vegetative cells of bacteria plus some protein.

This process is not used extensively on a commercial basis.

2. USE OF HEATa. 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.

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.

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.

4. DRYING 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.

a. 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:-

• 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:-

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.

B. DEVELOPED PRESERVATIVES 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

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. Acid formation cause 1st sour flavor of milk, then coagulation of milk

gives solid jellylike curd or a weaker curd that releases clear whey. Lactic acid fermentation takes place in raw milk at room

temperature. In raw milk at temperature from 10-37 C, Streptococcus lactis cause

the souring, with possibly some growth of coliform bacteria, enterococci, lactobacilli,& micrococci.

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.

Some of lactobacilli can grow at still higher temperature above 50 C but produce less acid.

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 lactis-

produce 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.

4. PROTEOLYSIS 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. 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.

6. CHANGES IN MILK FAT

Milk fat may be decomposed by various bacteria, yeasts, & molds.

Changes occur in milk fat are:-

1. Oxidation of the unsaturated fatty acids:- yields aldehydes, acids, ketones & results in tallowy odors & taste.

2. Hydrolysis of the butterfat to fatty acids & glycerol by the enzyme lipase.

3. 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.

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 Fruity flavor by P. fragi A potato like flavor by P. mucidolens.

9. COLOUR CHANGES 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.

1. BLUE MILK:- an acid former Streptococcus lactis causes a deep blue color in milk culture.

2. YELLOW MILK:- Species of Flavobacterium can causes yellowness.

3. RED MILK:- Micrococcus roseus may produce a red sediment,

Yeast may produce red or pink colonies on the surface of sour milk

4. BROWN MILK:- result from Pseudomonas putrifaciens.

10. SPOILAGE OF MILK AT DIFFERENT TEMPERATURES1. 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 slaughter- mechanical, chemical, electrical- have little effect of contamination..

But each method is followed by sticking & bleeding, which can introduce contamination.

• 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 MEATS

BACTERIA:- 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…

1. USE OF HEAT 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:-

1. 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. Meats that are heated enough to kill part of the spoilage micro-organisms 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 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

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.

4. PRESERVATION BY DRYING 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. 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. 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.

Nitrate used as a color fixative & has some bacteriostatic effect in acid solution.

Sodium chloride attributed most preservative effects of the curing agent.

Salts, Sugars, & meat protein combine to lower the Aw value of the cured meats.

There are 4 methods for introducing curing agents into meat:-

1. The dry cure- dry ingredients are rubbed into the meat.2. The pickle cure- the meats are immersed into a solution of the ingredients.3. The injection cure- a concentrated solution of the ingredients is injected by

needle into arteries of the meat.4. The direct addition method- the 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:-

Smoking has two main purposes:-1. To add desired flavors.2. 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.

7. 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 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 methods-1. The antibiotic may be fed to the animal over a long period.2. It may be fed to more intensively for a short period before

slaughter, 3. It may be infused into the carcass or its part of it.4. 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 Raw meat is subjected to change by its own enzymes & by

microbial action & its fat may be oxidized chemically.

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.

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

Factors that influence the growth of microorganisms to cause spoilage are as..

1. The kind and amount of contamination with microorganisms & the spread of these organisms in the meat.

2. The physical properties of meat- The amount of exposed surface of the flesh influence

on the rate of spoilage.3. The chemical properties of meat- The moisture content of the meat determine organisms

to grow.4. Availability of oxygen- Aerobic conditions at the surface of meat are favorable

to yeasts, molds & aerobic bacteria.5. Temperature- Low-temperature organisms can grow on stored

temperature of meat i.e. not far above freezing.

GENERAL TYPES OF SPOILAGE OF MEATSPOILAGE UNDER AEROBIC CONDITIONS:-

1. Surface slime- which may be caused by species Pseudomonas,

Leuconostoc, Bacillus etc. 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. Lipolytic bacteria may cause lipolysis.

4. Phosphorescence- Uncommon defect caused by luminous bacteria. 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.

Souring is term applied to almost any defect, that gives a sour odor may be due to volatile acid.

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 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:-

1. 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 from-a. Action of meat own enzymes during ripeningb. Anaerobic production of fatty acids or lactic acid during

ripening.c. 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. 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.

THANK YOU