Department of microbiology microbial food technology group a diploma in quality assurance in microbiology diploma

Micro organisms are capable of active growth at temperatures well below freezing to temperatures above

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Micro organisms are capable of active growth at temperatures well below freezing to temperatures above

1000c.But each individual species has a far more restricted temperature range in which it can grow. The range is determined largely by the influence that temperature has on cell membranes and enzymes and, for a particular organisms, growth is restricted to those temperature at which its cellular enzymes and membranes can function.

The relationship between growth rate and temperature for many microorganisms can be is illustrated.

  • A is the minimum temperature, i.e., the temperature below which no growth occurs. At temperatures below the minimum, the properties of cell membrane change so that they can no longer transport materials into the cell.

  • B is the optimum temperature, i.e., the temperature at which the organisms grows at its fastest rate.

  • C is the maximum temperature, i.e., the temperature above which no growth occurs. At temperature above the maximum enzymes become denatured and cease to catalyze essential cell reactions. These temperatures also damage the proteins and lipids in the cell membrane, which cease to function normally. So membrane collapse and the cell breakdown (thermal lysis).

The Cardinal temperature for Escherichia coli is

  • Minimum : 8oC

  • Optimum : 28oC

  • Maximum: 47oC

The minimum and maximum temperatures for growth normally quoted for an organisms depend on the

Other factors that influence growth also operating at an optimum, e.g., pH and water activity. If these environmental factors move way from the optimum then the minimum temperature for growth will increase and the maximum temperature decrease. For example,The minimum growth temperature for the food poisoning organism Staphylococcus aureus is 6.7oC and the maximum 48oC when the organism is grown at the optimum ph of 7.0 and optimum water activity of 0.99. if the pH of the environment is reduced to pH 5.0 and the water activity reduced by the addition of 3.0% sodium chloride to the growth medium, then the organism will no longer grow at 48’C and the minimum temperature is increased to 30’C

On the basis of their cardinal temperatures for growth, microorganisms can be divided into five groups:

  • Mesophiles

  • Obligate psychrophiles

  • Psychrotrophs

  • Thermophiles

  • Extreme thermophiles

Some microbiologist in factor, recognize a sixth category; facultative thermopiles, i.e., organisms that

have an optimum in the mesophilic zone but can grow well into the zone in which thermopiles grow rapidly.

Groups of Microorganisms based on growth temperatures.



Optimum oC

Maximum oC

Obligate psychrophiles
















Extreme thermophile




Mesophiles (organisms adapted to growth in the middle Temperature Zone)

Adaptation man and other warm-blooded animals, and water in tropical and temperature climates. An important characteristic of mesophiles is their lack of ability to growth at chill temperature (-1 to 5’C).

Example:- Bacteria, Yeasts & moulds

Many food spoilage organisms are also mesophilic.

Temperatures for toxin production by Staphylococcus aureus

Obligate psychrophiles(cold loving organisms)

Adaptations=> Arctic and Antartic Oceans, and land masses where temperatures are low throughout the year(land below 0’C and oceans 1-5’C).



Adaptation => water and soil in temperate climate(relatively high summer temperatures and low winter temperatures). Minimum temperatures recorded for bacteria in this group are as low as –6.5 oC (Pseudomonas fragii), - 10 oC(moulds) and –12.5 oC( the yeast Debariomyces hansenni).

Psychrotrophs are called facultive psychrophiles, referring to psychrophiles with the ability to grow at relatively high temperatures.

Psychrotrophs are a very important group of organisms causing the spoilage of foods hed at chill temperatures either on melting ice or in the refrigerator.





















In psychrotrophs, a higher amount of unsaturated fatty acid appears to maintain the plasma membrane in a liquid and mobile state at temperature below 5 oC. This ensures that the membrane is biologically active and capable of absorbing nutrients at low temperature.


Thermophiles are active in soils heated by sunlight compost heaps and silage, where the temperature can reach as high as 70 0C. Thermophiles are responsible for the spontaneous combustion of straw and hay. When the hay becomes damp, mesophiles grow; their metabolic processes generate heat and, because of the high level of insulation in the stack, the temperature moves up into the thermophilic zone .Growth of thermopiles takes over, increasing the temperature even further (up to 70 0C plus), when chemical oxidation causes the stack to spontaneously combust.

Few thermophiles have any significance in foods. Bacillus stearothermophilus, Clostridium thermosaccharolyticum and desulfotomaculum nigrificans(Clostridium nigrificans) are bacteria that cause the spoilage of canned foods stored at elevated temperatures that allow thermophiles to grow.

Three factors seems to be involved:

  • The cell membrane of thermophiles are abnormally stable because of a high content of saturated fats.

  • Cells proteins, including enzymes, are unusually heat stable.

  • The ribosomes are heat stable.

What effect does temperature have on the lag phase of growth?

Temperature has a very important effect on the lag phase of growth. As the temperature moves towards the minimum, not only dies growth rate decrease but the length of the lag phase increases. This has important consequence in relation to the preservation of foods at chill temperatures. The increase in storage life of foods held at chill temperature is associated not only with a decrease in the growth rate of spoilage organisms but also in an extension of the lag phase, when the population is not increasing in size. This increase in the length of the lag phase may be as important as decrease in growth rate. The effect of temperature on length of the lag phase and the rate of growth of psychrotroph is illustrated. The effect is not linear. A psychrotroph having a lag phase of 1 hour at its optimum(25 0C) may have lag phase of 30 hours at 5 oC and 60 hours at 0 oC. At temperatures very close to the minimum, lad phases may become very long indeed; 414 days has been recorded for some organisms.


Microbial cells can be damages when they are cooled from ambient to chill temperatures, a phenomenon known as chilling injury. There are two types of chilling injury.

  • Cold shock (Direct chilling injury) is associated with the process of cooling foods from ambient temperature to chill temperature. The level of injury depends on the rate at which the food is cooled. More cell damage occurs at slow rates of cooling than with fast rates. This type of damage seems to be caused by changes in the structure of the cell membrane resulting in the leakage of important cell metabolites, e.g., amino acids and ATP from the cell. Actively growth cells are more susceptible than stationary phase cells.

  • Indirect chilling injury is associated with holding food at chill temperatures for prolonged periods(several days) and is independent of the rate at which the food has been cooled, this type of injury seems to be caused by lack of exchange of materials with the environment leading to the accumulation of toxic metabolic products and/or the depletion of important cell metabolites such as ATP resulting in cell starvation and, eventually, death.

Example:- Salmonella Sp.
How does Freezing cause cell injury and death?

Cells injury death caused by freezing depends on the cooling rate as follows:

  • Slow freezing.

When cooling is slow (freezing rates that occurs in domestic freezers) ice crystals from outside the

cell. This causes an increase in the concentration of solute in the environment outside the cell followed by plasmolysis, cell shrinkage and eventually death. There is no evidence hat any mechanical damage is associated with the formation of ice crystals outside the cell. This type of freezing damage is the most lethal.

  • Fast freezing:-

When cooling is fast (freezing rates used in the food industry) ice crystals form inside cells. The

mechanism by which fast freezing causes damage is not well understood but possibilities are:

  1. Mechanical damage to cell membranes and DND molecules cause by ice crystals;

  2. An increase in the concentration of internal cell solutes leading to pH changes and an increase in ionic strength which in turn damage cell protein and nucleic acids;

  3. Formation of gas bubbles during thawing which cause mechanical damage to cell membranes.

  • Ultra fast freezing:-

When cooling is ultra fast (freezing rate produced by plunging cells into liquid nitrogen at –196’C)

water freezes to form a glass-like substance and the formation of damaging intracellular ice crystals is reduced. Cell damage is minimized and most of the injury to cells appears to be associated with thawing rather than the freezing process.


Cells that are injured but not killed can recover after thawing as long as there is an ample supply of nutrients (damaged organisms often have growth factor requirements that are not normally evident) and the environment does not contain inhibitors. Injured cells will recover quite readily in thawed foods. Cells of food poisoning organisms that are injured rather than killed


  • The Rh of the storage environment is important both from the aw within foods & the growth of microorganisms at the surfaces. When the aw of a food is set at 0.60, it is important that this food be stored under conditions of Rh that do not allow the food to pick up moisture from the air & thereby increase its own surface & subsurface aw to a point where microbial growth can occur. When foods with low aw values are placed in environments of high Rh the foods pick up moisture until equilibrium has been established.

  • Likewise, foods with a high aw lose moisture when placed in an environment of low Rh. There is a relationship between Rh & temperature that should be borne in mind in selecting proper storage of foods. In general, the higher the temperature is, the lower is the Rh & viceversa.

  • Foods that undergo surface spoilage from moulds, yeasts & certain bacteria should be stored under conditions of low Rh. Improperly wrapped meats such as whole chickens & beef cuts tend to suffer surface in the refrigerator much before deep spoilage occurs, due to the generally high Rh of the refrigerator & the fact that the meat spoilage flora is essentially aerobic in nature, the changes of surface spoilage in certain foods by storing under low conditions of Rh, it should be remembered that the food itself will lose moisture to the atmosphere under such conditions & thereby become undesirable.

  • In selecting the proper environmental conditions of Rh, consideration must be given to both the possibility of surface growth & the desirable quality to be maintained in the foods. By altering the gaseous atmosphere, it is possible to retard surface spoilage without lowering Rh.


  • The storage of food in atmosphere containing increased amounts of CO2 upto about 10% is referred to as controlled atmosphere [CA] or modified atmosphere [NA] storage. Usage of this is employed in many countries with apples & pears. The concentration of CO2 generally does not exceed 10% & is applied either from mechanical sources or by use of dry ice (solid CO2).

  • CO2 has been shown to retard fungal rotting of fruits caused by a large variety of fungi. The mechanism is unknown, but it acts as a competitive inhibitor of ethylene action.

  • Ethylene seems to act as a senescence factor in fruits, and its inhibition would have the effect of maintaining a fruit in a better state of natural resistance to fungal invasion.

  • Ozone added to food storage environments has a preservative effect on certain foods.

  • At levels of several parts per million, this has been tried with several foods and found to be effective against spoilage microorganisms.

  • It is a strong oxidizing agent; it should not be used on high lipid content foods, since it would cause an increase in rancidity.

  • Both CO2 ozone are effective in retarding the surface spoilage of beef quarters under long term storage.

5.Explain about contamination and spoilage of vegetables and fruits.


  • Spoiled food may be defined as food that has been damaged or injured so as to make it undesirable for human use.

  • Food spoilage may be caused by insect damage, physical injury of various kinds such as bruising and freezing, enzyme activity, or microorganisms.

  • It was estimated that 20 % of all fruits and vegetables harvested for human consumption are lost through microbial spoilage by one or more of 250-market diseases.

  • Vegetables and fruits are fresh, dry, frozen, fermented, pasteurized or canned.


  1. During harvesting => boxes, lugs, baskets, trucks, containers.

  2. Soil

  3. During transportation.

  4. Mechanical damage => processing / trimming

  5. Washing preliminary soaking distribute spoilage organisms.

    1. Re-circulated or reused water may add micro organisms (washing with detergent/ germicidal solution reduce number of micro organisms).

  • Storage containers / bins

  • Handling

  • Spray water and ice growth of psychographs

  • Equipment tables, blanches, press, filters, cloth, wooden surface.

General microbiological profile of harvested fruits and vegetables:

Vegetables: Fruits:



Fusarium, Alternaria, Aureobasidium, Penicillium, Sclerotinia, Botrytis, Rhizopus

Pseudomonas, Alcaligenes





Lactic acid bacteria Corynebacterium.



Cladosporium Phoma Trichoderma

And above organisms.

Pseudomonas, Alcaligenes





Lactic acid bacteria Corynebacterium

Some microorganisms involved in the spoilage of fresh vegetables.




Corynebacterium sepedonicum


Ring rot of tuber

Pseudomonas solanaceanum


Soft rot

Erwinia carotovora



Soft rot

Streptomyces scabies



Xanthomonas campestris


Black rot


Botrytis cinerea


Grey mould

Botrytis allii


Neck rot

Mycocentrospora acerina


Liquorice rot

Trichothecium roseum



Pink rot

Fusarium coeruleum


Dry rot

Aspergillus alliaceus



Black rot

Preservation of vegetables:

  1. Asepsis sanitization of equipments.

  2. Removal of microbes washing chlorinated water, lye solution, and detergents.

  3. Blanching / trimming / blanching washing with hot water at 90-100c, inactivate food enzymes and surface sterilization).

  4. Heat canning

  5. Chilling cold water i.e., refrigerator, vaccum cooling

  • Hydro cooling cold H2O spray

  • Controlled atmosphere Co2 / ozone. Eg potatoes 2.2 to 4.4 c

  1. Freezing survival of Micrococus, Achromobacter, Enterobacter, spores of Clostridium and Bacillus.

  2. Drying explosive puffing

Small pieces of diced partially dehydrated vegetables are placed in a closed rotating chamber.
Heat applied, chamber is pressurized to a pre-determined level
Pressure is released instantaneously
Results internal loss of water
Increased porosity simplifies further drying

8. Preservative rutabagas and turpips are parafinned.

    • Lettuce, beets, spinach => ZnCo3­ (to prevent mold).

    • Controls Fusarium on potato => biphenyl vapours, Co2 and ozone used.

    • Saueskraut / cauliflower / lemon => Nacl (2.25 to 2.5%)

      • High protein vegetable => Nacl (18.6 to 21.2%)

    • Brine solution

    • Salad freshers => sulfites

    • Sugars

9. Irradiation gamma radiation (insect) – potato, onion, garlic.

Preservation of fruits:

  1. Asepsis

  2. Removal of microbes => trimming

  3. Use of heat => blanching, canning=> fruit juices

Low PH food => tomatoes, pears, pineapple.

High PH food => berries

  1. Use of low T

Chilling => before chilling – propionate, borax, NaHCo3, biphenyl phenols, orthophenyl phenols, hypochloride, So2, thiourea, thiobendazole, dibromotetra chloroethane added to avoid shrinking and surface sterilization occurs.

  1. Controlled atmosphere =>increases Co2 and decrease O2 content (Co2 storage) to prevent molds).

  2. Modified atmosphere => 100% N2 (N2 gas storage).

  • Co2 storage apples, citrus, grapes, pears, plums,banana peaches

  • Ozone 2-3 ppm (strawberries, grapes, raspberries)

  • Ethylene ripening (color Changes)

  1. Freezing, drying dehydration, sulfuring, blanching

  2. Preservative Na, o- phenyl, phenates, waxes, hypochlorites, biphenyl alkaline

  • Wrapper I2­, S, biphenyl, O – phenyl phenol + hexamine, ozone, So2.


Kinds of spoilage

Organism involved


Bacterial soft rot

(Soft, mushy bad odour)

Erwinia carotovora, Ps.marginatus, clostridium sp, Bacillus sp.


Gray mold

Botrytis cinera (gray mycelium)


Rhizopus soft rot

R.stolonifer (Soft mushy black dot sporangia)


Anthracnose spots of leaves

Collectotfichum lindemuthianum C.coccodes


Aiternaria rots

Alternaria tenuis (greenish – brown / black spots)


Blue mold rot

Penicillium digitatum (bluish green rot)


Downy mildew

Phytophthora, Bremia (white woody masses)


Watery soft rot

Sclerotinia sclerotium (vegetable)


Stem end rot

Diplodia, atternaria, Fusarium


Black mold rot

Asp,niger (Dark brown – black smut)


Black rot



Pink mold rot

Trichothecium roseum


Fusarium rot



Green mold rot

Cladosporium sp,Trichoderma sp


Brown rot

Sclerotinia sp


Sliminess / souring

Saprophytic bacteria in piled, wet, heating vegetables

  • Fungal spoilage of vegetables often results in water soaked, mushy areas, while fungal rots of fleshy fruits such as apples, peaches frequently show brown or cream colored areas in which mold mycelia are growing in the tissue below the skin and aerial hyphae and spores may appear.

  • Some types of fungal spoilage appear as dry rots, where the infected area is dry and hard and often discolored.

  • Rots of juicy fruits may result in leakage.

  • Molds are favoured due to deficiency in vitamin B.

  • Spoilage may be by;

    • Damage by mechanical means, plant pathogens or bad handling will favors entrance.

    • Direct contact with moist soil – roots, tubers or bulbs. eg carrots, beets, radishes, potatoes

    • Direct contact with surface soil. Eg: strawberries, cucumbers, and peppers.

Spoilage of fruit and vegetable juices:

1. Molds can grow on the surface of juices due to high moisture content, acidity, low in sugar.

2. The removal of solids from the juices by extraction and sieving raises the oxidation – reduction potential and favors the growth of yeasts.

3. Most fruit juices are acid enough and have sufficient sugar to favors the growth of yeasts.

4.Deficiency of vitamin B discourages some bacteria.
Yeast / acetic acid

5. Fruit juice Alcohol acetic acid

Mold bacteria

Lactic acid bacteria

Lactic acid

6. Fruit juices undergo changes like;

a. LA fermentation of sugars L.pastorianus


Leuonostoc mensenteroides (apple or pear juice)

Lactobacillus rabinosus



b. Fermentation of organic acids of juice by LA bacteria

i.e, malic acid lactic and succinic acids

quinic acid dehydroshikimic acids

Citric acid lactic and acetic acids

c. Slime production by L.mesenteroides, L.brevis and L.plantarum in apple juice and L.plantarum and streptococci in grape juice.

7. Vegetable juices also contain a plentiful supply of accessory growth factors for microorganisms and hence support the good growth of fastidious lactic acid bacteria.

8. Acid fermentation of raw vegetable juice by these and other acid forming bacteria causes yeasts and molds to growth.
6.Explain about contamination and spoilage of eggs (poultry products)



  • The hen’s egg is an excellent example of a product that normally is well protected by its intrinsic parameters.

  • Externally, a fresh egg has three structure, each of which is effective to some degree in retarding the entry of microorganisms

    1. The outer, waxy shell membrane

    2. The shell

    3. The inner shell membrane.

  • Internally, lysozyme is present in egg white effective against gram-positive bacteria.


  1. Faecal.

  2. Soil

  3. Cage => shell => gram positive organisms, Salmonella, Streptococcus, Staphylococcus, Micrococcus, Sarcina, Bacillus, Alcaligenes, Flavobacterium, Proteus, Serratia, Aeromonas, molds, like Penicillium, Mucor.


Eggs have some protective barrier;

a. Shell => cuticle / bloom (layer on shell, polished) if cuticle is removed then organism enters.

b. Shell membrane.

c. Albumin content => anti Proteolysis factor

  1. Asepsis => equipment sanitize, handling must be care and prevent contamination.

  2. Removal of microbes => dry cleaning by sandblasting (washing with hot water)=> removes bloom so not advisable.

* Mechanical egg washer;

1 % hypochlorite => to sanitize equipment.

2% acetic acid => very effective but reduce the size of shell => don’t store, use immediately as bloom removal.

  1. Use of heat => heating in water but avoid coagulation

i.e, 57.5 C => 800 sec

60 C => 320 sec

    • Heating in oil => 60c for 1 min

54.4 C for 30 min

    • Immersion in hot detergent sanitizer 43.3 to 54.4 c

    • Thermo stabilization => slight coagulation of albumin.

    • Pasteurization => before this add Aluminium and salt to adjust PH

  1. Use of low T chilling -1.7 to –0.55c with air circulation.

Rh is 70 to 8 (6 months)

    • For this eggs are selected by candling

This removes

      1. Increased air sac

      2. Infected eggs

      3. Rotten eggs

    • Avoid moisture on the shell

    • Impregnation of eggshell with colorless, odorless, oil improves their quality.


    • Rinse 200-500 ppm of Cl2 / I2

    • Frozen in 30- or –50lb tin can/ container

    • Add 5% sugar / salt/ glycerol before freezing

    • T –17.8 to –20.5 C


    • Removal of glucose prevent browning / maillard rxn

    • Removal of glucose may be by

    • 1. Fermentation using Group.D stretococci, Enterobacter aerogenes or Saccharomyces sp.

    • 2. Using the enzyme glucose oxidase at 10c

Dryers used are

Spray dryer, Drum, Rotor, air, pan and tunnel dryer (60-71C)

    • Final moisture content => 5 to 1% was retained

    • Before drying pasteurization was carried out

    • After drying some organisms can act as contaminants from handlers, equipment or through air and soil. They are Micrococci, str. facealis, coliforms, Salmonella, spore formers and molds.

6. Use of preservative waxing, oiling prevent O2 entry and maintain dry shell.

a. Materials used for dry packaging of eggs are salt, lime, and saw dust, sand and ashes.

b. Solution of sodium silicate for dipping.

c. Others => borates, permanganates, benzoates, salicylates, formats.

d. Washing of eggs with hot solution of germicides;

  1. Hypo chlorites

  2. Ly solution

  3. Acids

  4. Formalin

  5. Quaternary ammonium compounds

  6. Sealing of shells solution of dimethylourea inhibits mold growth.

  7. Mycostatic sodium pentachlorophenate

  8. Fumigation gaseous ethylene oxide

  9. Co2 + ozone (CA) 0.6 pp for clean eggs

1.5 ppm for dirty eggs

  1. N2 storage.

  2. – 0.55 C to 90% Rh keeps eggs fresh for 8 months

  3. Radiation  rays is used to prevent salmonella.


  1. General appearance.

  2. Candling with transmitted light.

  3. Broken egg

These are obvious for spoilage.

Defects in fresh egg:

Fresh eggs may have cracks, leaks, loss of bloom or glass, stained or dirty spots on exterior as well as meat spots (blood clots), general bloodiness, or translucent spots in the yolk when candled. From among these, any breaks in the shell or dirt on the egg will favors spoilage on storage.

Changes during storage:

  1. Microbial.

  2. Non – microbial

1. Changes due to non- microbial agents:

  1. Egg breakage.

  2. Storage of old eggs results in protein denaturation.

  3. Air sac increased.

2. Changes due to microbes:



Green rots

Pseudomonas. fluorescens

Bright green colour, fruity / Swedish odour, not detected by candling.


Colorless rots

Pseudomonas, Acinetobacter, Alcaligenes, coliforms.

Identified by candling, odour, white incurstation


Black rots

Proteus, Pseudomonas, Aeromonas, Pr.melanovegenes

Odour – H2S, putrid – muddy brown.


Pink rots


Pinkish ppt of yolk


Red rots


Mild odour



Enterobacter, alcaligenes, Escherichia, Flavobacterium, Paracolobacterium


1. Pin spot molding:

  1. Penicillium yellow / blue / green spot

  2. Cladosporium dark green / black spot

  3. Sporotrichum pink spot

2. Superficial fungal spoilage:

*Fuzz / whiskers on shell during storage increase RH and no air circulation.

Fungal rotten Penicillium, Cladosporium, Sporotrichum, Mucor, Thaminidium, Botrytis, Alternaria.

3. Fungal red rot Sporotrichum

4. Black rot Cladosporium Achromobacter peolens

Pseudomonas. graveolen

Off flavour / musty odour

Pseudomonas. mucidolens

Bad odour (hay flavour) Enterobacter cloacae (due to faecal contamination)

Cabbage water flavour (fishy flavour) E.coli (due to faecal contamination).
7.Explain about contamination and spoilage of meat and meat product.


  • Meat are the most perishable of the important foods, in which the chemical composition of a typical adult mammalian muscle postmortem is presented.

  • Meat contain an abundance of all nutrient required for the growth of bacteria, yeasts,and molds, and an adequate quantity of these constituents exist in fresh meats in available form.

  • When spoiled meat products are examined, only a few of the many genera of bacteria, molds ,or yeasts are found.

  • Almost all cases one or more genera are found to be characteristic of the spoilage of a given type of meat product.

Frequently isolated microorganisms from meat

S. no


Microorganisms isolated


Fresh and refrigerated meat




















Processed meat and cured meats


Lactobacillus and other lactic acid bacteria.
















  1. Lymph node (more number of micro organisms) staphylococcus, streptococcus, clostridium, salmonella

  2. Flesh => good culture media as it contains protein, carbohydrate, lipids and vitamins.

  3. Bleeding, handling, processing (enter – full circulation in body). Skimming, cutting, knife.

  4. Hide, hooves, hair

  5. Soil, H2o, feed, manure, air, wood (slaughter house)

  6. Intestinal organism coli forms, pathogenic fungi

  7. Container, boxes

  8. Meat surface – molds => Cladosporium, Sporotrichum, Geotrichum, Thamnidium, Mucour, Penicillium.

  9. Pseudomonas, Acinetobacter, Moraxella, Alcaligenes, Micro cocci, Flavobacterium, Proteus

    • utensil contamination and salt tolerant

    • Found in meet products.

Characteristics of some Gram negatives associated with meat.

Gram negative
Not fermentative in OF medium

Oxidase +ve Oxidase –ve

Motile non motile non motile

Pseudomonas Acinetobacter

(formerly Moraxella) (Achromobacter)


(formerly Moraxella-like)

Polar flagella

Not oxidase Oxidase

in OF medium in OF medium

Pseudomonas Pseudomonas

Shewanella (Achromobacter



1. Asepsis:

    • Sanitation and H2o spray (before cutting) (utensils)

    • After cutting => hot H2O / detergents etc

2. Use of heat:

  1. Commercially sterile (Self stable)=> 90C (11 lbs)

Process by increasing heat + Nacl / salt solution

  1. Non self stable => stable for some pots (controlled atm) => heat process (65C with 22 lbs) – canning => refrigeration.

3. Use of low T:


    • -1.4 to –2.2C

    • Particularly maintained or else spoilage => beef => 30 days

    • Pork, lamb, mutton => 1-2 weeks

    • Real (calf meat) => shorter period

    • (CA) + Addition of Co2 + ozone => increase Co2 / ozone leads to formation of metmyoglobin, from myoglobin change the colour.

    • Co2 10 to 30% for most meet

        • 100% for bacon.

    • ozone => 2.5 to 3 ppm (92% Rh) => 60 days maintained

    • Chilling T => Pseudomonas, Acinetobacter, Moraxiella, Alcaligenes, Pediococcus cerevisiae, (salt tolerant) => does not effect in curing.


      • -1.22 to –28.9 C (Pseudomonas, Moraxiella, Acinetobacter, Alcaligenes, Micrococcus, Lactobacillus, Flavobacterium, Proteus).

4. Use of radiation:

      1. UV [air] surface of meat products

      2.  rays Depend meat products [Hard Meat – Increase  rays]

      3. Increase  rays – Pork

      4. 20 – 70 K-Grays – Normal

5. Drying:

        • Slice & Dried

        • Sodium nitrites – to dry the surface of meat

6. Freeze drying:

        • Meat Products generally are not freeze

        • Bleeding – removal of liquid to outside

        • Freeze burn – Change in colour – brown colour

        • Smoking

7. Curing:

        • Addition of Salt

        • NaCl – 15% salt (immerse meat)

          • 24% salt [inject to meat)

        • Preservating & flavouring agent

          •  NaNo3  Colour Fixative [bright red] & bacteriostatic

        • Increased concentration lead to brown colour

        • Sugar – adds flavour and serves as an energy source for nitrate – reducing bacteria

4 Methods of introduction of curing agents into meat;

  1. Dry

  2. Pickle

  3. Injection

  4. Direct-Addition

Spoilage of Meat:

  • Oxidation occurs

  • Due to protease, lipases

Factors that influence the invasion of Microbes:

  • Load in the gut

  • Physiological condition of animal

  • Method of killing & bleeding

  • Rate of cooling

Aerobic condition influences the growth of bacteria, molds, yeast.

Factors that influence the growth of Microbes in Meat:

  • Kinds of no. of microbes

  • Physical properties of meat

  • Chemical properties of meat  R, PH [5.7 to 7.4 based on glycogen], chemical composition of meat.

  • Availability of O2.

  • Temperature

  • Animal pathogen  Salmonella, Camphylobacter, Pseudomonas


Spoilage under Aerobic Conditions:

1. Surface Slime:

Pseudomonas, Acinetobacter, Alcaligenes, Moraxella, Streptococcus, Leuconostoc, Bacillus, Micrococcus, Lactobacillus.

2. Discolouration of Meat Pigment:

  • Autolysis also occur

  • Generally meat has heamoglobin; myoglobin due to oxidation produces metmyoglobin.


Hb, Myoglobin Oxidation Metmyoglobin

[Purplish Pink] [Brown]

  • Blooms i.e., Red  Green / Brown / Grey

  • Oxidizing compounds peroxidase, H2S results in spoilage.

  • Organisms involved may be Lactobacillus sp., Leuconostoc sp and other heterofermentative organism

3. Changes in Fat:

    • Oxidation of unsaturated fats catalyzed by light & copper

    • Lipolytic organisms  Pseudomonas, Achromobacter yeast

    • Oxidative rancidity (degradation of fat) results in tallowy odour

4. Phosphorescence:

  • Luminous bacteria

  • Photobacterium on the surface of meat

5. Discolouration of meat due to Bacterial Pigment:

Red spot

Serratia marcesens


Micrococcus, Flavobacterium, Chromobacter lividium

Greenish / Blue / Brownish Black

Proteus & others

6. Taint [Off flavour and odour]:

  • By yeast, Actinomycetes results in musty / earthy flavour

  • Yeasts produce acetate, formate, butyrate & propionate.

Aerobic Growth of Molds:

1. Stickness

2. Whiskers  Thamnidium Chaeotocladioides, T.elegans, Mucor, M.Mucida, M.raceonogus, Rhizopus.

3. Black Spot  Cladosporium herbarum

4. White Spot  Sporotrichum Carmi

5. Green pathches  P.expansum, P.oxalium, P.asperulum.

6. Decomposition of Fat

7. Taint  Musty flavour  Thaminidium taint by Thaminidium sp.

Spoilage under Anaerobic Conditions:



  • Due to formate, acetate, propionate, lactate, succinate and fatty acids.

  • By clostridium & other facultative anaerobes

  • After protein / fat lysis in aerobic leads to anaerobic condition


. Putrefaction

  • Anaerobic decomposition of protein leads to fowl smell and results in production of H2S, mercaptans, indole, skatole, NH3, amines

  • Caused by Clostridium and other facultative anaerobes



  • Bone Taint  Souring / putrefaction next to bones

Spoilage of Different Kinds of Meat:

Fresh Meat:



Pseudomonas, Actinetobacter, Moraxiella


Shine form

LA bacteria


Green discolouration

Lactobacillus, Leuconostoc



Streptococcus, Pediococcus, Brevibacterium

Fresh Beef:

  1. Oxidation of mycoglobin & Hb.

  2. White, green, black, greenish blue, yellow, brown, black spots.

  3. Phosphorescence.

  4. Shine formn  bacteria, yeast

  5. 10 C Meat  Pseudomonas

  6. Whisters & Stickiness




at RT



Near freezing


Low Temperature

Pseudomonas, Acinetobacter, Moraxella, Micrococcs, Flavobacterium, Alcaligenes


High Temperature

Bacillus, Clostridium, E.coli, Micrococcus, Sarcina, Mucor, Lactobacillus, Leuconostoc, Penicillium, Alcaligenes, Streptococci, Enterobacter, Proteus, Pseudomonas

Fresh Pork Sausage:



0 – 11 C

Lactobacillus,Micrococcus, Microbacterium


Colour spot



Dark spot

Alternaria [on refrigeration]

Cured Meat:


Cured meat

Salted Meat [NaCl / NaNo3]



Anaerobic NaNo3  favours LA bacteria, G+ve orgs, yeasts, molds.

Dried Beef / Beef Hams:



H2O, Rh






LA bacteria


. Red

Halobacterium salinarium, Bacillus



Ps.syncyaneae, Penicillium spinulosum, Rhodotorula.


. Gas in jars



Co2 in jars



Slime  Moisture  Micrococci & Yeasts

 Decrease  Fuzziness discolouration  Molds

Sour Leuconostoc , Lactobacillus

Swell package  due to Co2 by heterfermentative LA bacteria.

Fading red colour to chalky grey  Bacteria

Greening of sausage  Leuconostoc, Lactobacillus

Production of Nitric oxide  Nitrate reducing bacteria.


Mold Aspergillus, Alternaria, Mucor, Rhizopus, Penicillium


* Souring  Alcaligenes, Bacillus, Pseudomonas, Lactobacillus, Proteus, Micrococci.

* Putrefaction  Odour – Mercaptans, H2S, Amines, Indole.
Refrigerated Packed Meat:

* Due to packaging film & Co2Pseudomonas, Acinetobacter, Moraxella

* Off flavour, shine & putrefaction.

8.Explain about contamination and spoilage of fish and seafood.


  • Both salt-water and fresh water fish contain comparatively high levels of proteins and other nitrogenous constituents.

  • The carbohydrate content of these fish is nil. While fat content varies from very low to rather high value depending upon species.

  • Of particular importance in fresh flesh is the nature of the nitrogenous compounds. the relative percentage of total –N and protein-N are presented from which it can be seen that not all nitrogenous compounds in fish are in the form of proteins.

  • Among the non-protein nitrogen compounds are the free aminoacids, volatile nitrogen bases such as ammonia and trimethylamine, creatine, taurine, the betaines, uric acid, anserine, carnosine, and histamine.

(CH3) 3 N O

Trimethylamine oxide

TMO reductase

(CH3) 3 N



  1. Flora of fish depends on the waters in which they live.

  2. Slime that covers the outer surface of fish is Pseudomonas, Aeromonas, Acinetobacter, Moraxella, Alcaligenes, Micrococcus, Flavobacterium, Corynebacterium, Sarcina, Serratia, Vibrio, and Bacillus.

  3. Northern Waters  Psychrophiles

Tropical Waters  Mesophiles

Fresh Waters  Aeromonas, Lactobacillus, Brevibacterium, Alcaligenes, Streptococcus.

4. Intestine of fish  Alcaligenes, Pseudomonas, Flavobacterium, Vibrio, Bacillus, Clostridium, Escherichia.

  1. Boats, boxes, bins, fish houses & fishers become heavily contaminated with three bacteria & transfer them to fish during clearing.

  2. Oysters, other shell fish  Pick up organisms from soil & water

Alcaligenes, Flavabacterium, Moraxella,

Acinetobacter, G+ve sp.

7. Shrimps, Crabs, Lobsters s  Bacillus, Micrococcus, Pseudomonas, Acinetobacter,

Moraxella, Flavobacterium, Alcaligenes, Proteus.

Fish and fish products:

Cooked, frozen products

Frozen fish Vacuum packing

Dried fish Fresh fish Canned

Fermented fish Marinades

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