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Outline
I. Introduction to Food spoilage
II. Spoilage of dairy Products
III. Spoilage of Eggs
IV. Spoilage of Poultry
V. Spoilage of Meat and meat products
VI. Spoilage of Canned products
VII.Spoilage of Cereals and cereal products
VIII. Spoilage of Fruits and Vegetables
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…………..…………………to be continued
B. Condensed Milk
 Source of Contamination
 In superheated condensed milk temperature is raised to 65.6-76.7℃ which
destroy vegetative cells of bacteria hence contamination is more frequently
occurred by aerobic spore formers e.g., Bacillus sp. whose proteolytic enzyme
cause curdling.
C. Evaporated Milk
 Canned and heat processed under steam
 Spoilage: If heating is not adequate causes
 Swelling of Can: due to presence of Gas forming anaerobic spore formers e.g.
Clostridium sp.
Milk constituents (nutrients) + iron of can ------- Hydrogen gas ------Bulging of Can
 Coagulation of milk: Varies from soft curdling to solid curd like texture.
• Caused by Bacillus cereus, B. subtilis and B. coagulans
 Bitterness: Results of proteolysis of milk protein
• By sp. of Bacillus and Clostridium sp.
 Spoilage resulting from leakage: Swelling – Coliform bacteria and yeast;
Coagulation – Streptococci ; Bitterness – Cocci sp.
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C. Butter
 Salted butter: Less microbial growth
 Butter manufactured from pasteurized milk and also stored at below -17.8℃
hence no microbial growth.
 But flavor of butter being delicate small amount of growth changes the flavor.
 Flavor defects:
 Undesirable flavor: comes from cream (feed of animal like onion, garlic, poor
silage; from atmosphere like volatiles products like kerosene, fly sprays etc)
 Rancidity: Lipolytic bacteria (Lipase activity) and molds
 Yeasty Flavor: Yeast
 Cheesiness: Lactobacilli
 Unclear flavor: Coliform bacteria
 Fishiness: Aeromonas hydrophilla
 Roquefort like flavor: Due to mold growth
 Surface taint or Rabbito: More in unsalted and low salt butter and caused by
Pseudomonas putrifaciens (Source fresh water, churner and equipement)
 Color defects: chiefly at surface
 Orange yellow spots: Geotrichum sp.
 Green coloration: Penicillium sp.
 Brown areas: Alternaria sp.
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D. Cheese
 Spoilage in Cottage cheese: Curd formation by lipolytic and proteolytic
microorganisms (e.g. Pseudomonas fragi and Alteromonas putrifaciens followed
by fruity rancid odour
 Surface discoloration: pigmented Flavobacterium
 Unclear flavor: E. Coli
 Pink spots on surface: Rhodotorula yeasts
 Yellow spots on surface: Candida glabrata
 Off white or tan yellow spots on surface: Geotrichum candidum
 Early gas defects in semi hard cheese: Enterobacter aerogenes, Coliforms,
Heterofermentative bacteria (Leuconostocs and Lactobacillus), yeast
 Late gas defects in semi hard cheese: Propionic acid bacterium and Clostridium
tyrobutyricum, C. perfringenes
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 Spoilage of Eggs and Poultry
 Freshly laid eggs are generally sterile but soon become contaminated with
numerous genera of bacteria from fecal matter from hen, by nest, during handling
and packaging.
 Defects in fresh eggs: Cracks, leaks, loss of gloss,
stained dirty spots favors spoilage on storage.
 Changes during storage:
 Untreated eggs lose moisture and losses wt.
 Shrinkage determined by candling
• More air space/ air cell --- Shrinkage
 White portion---Thinner and more watery
 Yolk membrane becomes weaker
 Microbial spoilage
 Egg shell and associated membrane, as well as lysozyme and high pH in egg
white (pH>9.0) prevent microbial penetration.
 Eventually m/o contaminating the shell and penetrate through pores (8-
10000) and reach to egg white and then grow in egg white to reach yolk
where it can grow and cause complete spoilage.
 Spoilage mainly caused by bacteria than molds.
 Salmonella sp. is of prime concern. 6

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 Bacterial spoilage
 Rots/ Fluorescent green rots:
• M/O - Pseudomonas fluorescens
• Bright green color of egg white and fruity smell
 Colorless rots:
• M/O - Pseudomonas sp., Acinetobacter sp. and certain coliform bacteria
• Fruity odour and cause contamination in Egg yolk.
 Black Rots:
• M/O - Proteus sp., Pseudomonas sp. and Aeromonas sp.
• Yolk become darkened and egg white is dark in color
• Putrid odour due to Hydrogen sulfide gas production
• Cause due to higher storage temperature (Room temp 20℃) than usual
storage temp (4℃)
 Pink rots:
• M/O - Strains of Pseudomonas
• Comes at later stage of green rots.
• Pinkish precipitation of egg yolk and white.
 Red rots:
• M/O - Serratia marcescens
• Mild odour
• Red discoloration of albumin and surface of yolk
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 Off flavors
• Mustiness: Occurred due to Achromobacter perolens, Pseudomonas
graveolans, P. mucidolens
• Musty/ earthy flavor: Streptomyces sp.
• Fishy odour: Escherichia coli
• Cold storage taste: From packaging material
 Fungal/ Mold spoilage
 Pin spot molding:
• Due to growth of small, compact colonies of mold on shell of egg or just
inside air cell/sac.
• Color varies with species of mold.
• Yellow, blue, green spots inside shell due to Penicillium sp.
• Dark green black spots observed due to Cladosporium sp.
 Superficial fungal spoilage:
• Due to storage atmosphere of high humidity
• In the form of fuzz or whiskers covering shell with growth.
• Freezing temp support mycelial growth but not sporulation
• M/O – Penicillium, Cladosporium, Sporotrichum, Mucor and Botrytis
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 Fungal rotting:
• Mycelium of molds grow through pores or cracks in egg.
• Results in Jellying of egg white and colored rots
• Fungal red rot by Sporotrichum
• Black rot by Cladosporium
• Hyphae of mold weaken yolk membranes and causes rupture, where its
growth is stimulated.
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 Spoilage of Poultry
 Source of contamination:
 Skin of birds may contain a large number of bacteria and also present in
feet, feathers and feces.
 Contamination of the skin and lining of the body cavity occurs during
washing, plucking and evisceration.
 Knives, cloth, air and hands and clothing of worker are intermediate
source of contamination.
 The process of sticking and bleeding also cause contamination.
 Since most sources of contamination is found during processing of poultry,
Hence now a days they are processed by a fully automated conveyor with
vacuum evisceration.
Signs of Microbial spoilage:
 Bacteria is the major cause of spoilage and intestine is the primary source.
 Enzymes contributes to the deterioration of dressed bird.
 Chief source of spoilage is bacteria and intestine id the primary source of
contamination.
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 Signs of Spoilage:
 Off flavor and odour
 Change in color
 Change in appearance (Feels slimy or tacky to touch)
 Eviscerated poultry stored at temperature below 10℃ mostly spoiled by
Pseudomonas and to a lesser degree by Yeast sp. (Torulopsis / Candida
glabrata and Rhodotorula sp.)
 Above 10℃ Micrococci is the predominate spoilage organism. Alkaligens
and Flavobacterium also cause spoilage.
 Frozen poultry products on spoilage often develops slime accompanied by
an off odour described as “tainted”, “acid”, “sour” and “dishraggy”. This is
caused by Shewanella putrifaciens, Pseudomonas fluorescens, P. fragi and
Alkaligens sp. etc.
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 Spoilage of Meat
 Source of contamination
 Exterior of animal i.e. animal hide and hair.
 External sources such as handling and processing
(from cutting boards, conveyer belts).
 Fecal contamination from intestine.
 during transportation (from carts and containers)
 During storage ( chilled storage - due to growth of psychrophiles)
 Invasion of tissue by Microorganisms
 Load in gut of animal: Starvation for 24 hr before slaughter recommended.
 Physiological condition of animal immediately before slaughter: If animal is
feverish or fatigued more bacteria will enter and therefore glycogen is used up
and pH will not drop and remains 7.2.
 Killing Methods: Better keeping quality, the better and sanitary methods of
Killing.
• Electronically stunned animals: More microorganisms
• CO2 stunning of animals: Less microorganisms
 Rate of Cooking: Rapid cooking reduces invasion of microorganisms.
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 Growth of microorganisms in meat
 Meat is an ideal culture medium for the growth of m/o because of
• High moisture content
• High in nitrogenous compound and minerals
• Fermentable CHO i.e. Glycogen
• Favourable pH
 Factors affecting growth of m/o
• Amount of contamination with microorganisms
• Physical property of meat: exposed surface has more load of m/o.
Grinding meat also increases surface area. Presence of air also favor
the growth of aerobic m/o.
• Chemical property of meat:
1. Moisture content: Dry meat - no growth
Little moist meat - mold growth
Moist meat - yeast
Very moist meat - Bacterial growth
2. Relative Humidity of storage atmosphere
3. pH: Higher pH is susceptible to spoilage
• Oxygen availability: More on surface and favorable to molds, yeast and
aerobic bacteria whereas within solid pieces conditions are anaerobic.
• Temperature: Meat should be stored at freezing temp. At room temp
mesophiles also cause spoilage e.g. Coliforms, Bacillus sp. and Clostridium sp.
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 Types of spoilage
 Spoilage under aerobic condition
1. Surface slime
• Favorable temp and availability of moisture
• M/O involved are Pseudomonas sp., Acinetobacter, Streptococcus, Leuconostoc,
Micrococcus and some sp. of Lactobacillus.
2. Changes in color of meat pigment
• Sp. of Lactobacillus, Leuconostoc causes greening of meat
• Red color turned into shades of green, brown due to production of oxidizing
compounds eg. Peroxides, hydrogen sulphide by bacteria.
3. Changes in fat
• Rancidity occurred to oxidation with off odour due to aldehydes and acids
• m/o involved are lipolytic sp. of Pseudomonas, Achromobacter and yeast
4. Phosphorescence
• Caused by Photobacterium sp. on the surface of meat
5. Surface color due to pigmented bacteria
• Red spot: Serratia marcescens
• Blue color on surface: Pseudomonas pyocyanea
• Yellow color: Micrococcus, Flavobacterium
6. Off odour and off taste
• Appear due to growth of bacteria on the surface
• Souring of meat occurred due to sour odour that may due to volatile acids e.g.
formic acid, butyric acid and due to growth of yeast.
• Actinomycetes responsible for musty/earthy flavor
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7. Spoilage caused by yeast
• Aerobic spoilage
• Sliminess, lipolysis, off odors, off taste and discoloration
8. Spoilage caused by aerobic gills of mold
• Stickiness due to excessive growth of molds on the surface of meat
• Whiskers: white fuzzy growth when meat is stored near freezing temperature. M/O
involved are Mucor mucido and Mucor racemosus.
• Black spot: due to Cladosporium herbarum and molds with dark pigments
• White spot: Sporotrichum carnis and Geotrichum sp.
• Green patches: due to Penicillium expansum and Penicillium oxalicum
• Decomposition of fats: hydrolysis of fat by lipases by spoilage microorganisms
• Off odors and off tastes: musty flavor due to mold growth
 Spoilage under anaerobic condition
• Facultative and anaerobic bacteria able to grow within meat and cause
spoilage such as
1. Souring
• Caused by formic, acetic, butyric, and other higher fatty acids and also by
organic acids such as lactic acids. It can result from
a. Meats own enzymes during ageing and ripening
b. Anaerobic production of fatty acids by bacterial actions
c. Proteolysis caused by fecal and anaerobic bacteria causing stinking sour
fermentation.
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2. Putrefaction
• Anaerobic decomposition of protein with the production of foul smelling
compounds like hydrogen sulphide, ammonia, indole (fecal odour), skatole
(three methyl indole) and amines.
• Caused by sp. of Clostridium and Pseudomonas
3. Taint
• Refers to souring and putrefaction next to boxes.
 Spoilage of different types of meat
1. Fresh meat
• M/O involved are Pseudomonas, Acinetobacter, Pseudomonas fragi, P.
lundensis, P. fluorescens, Psychrobacter immobilis (Gram negative aerobic
rods) and lactic acid bacteria of genera Lactobacillus sp., Leuconostoc sp.
and Streptococcus sp.
• LAB causes slime formation, Green discoloration and souring
2. Sausages
• Long chilling storage or storage at 10.5℃ favors growth of acid forming
Micrococcus, Candidus, Lactobacillus and Leuconostoc responsible for
fading of red color to chalky gray attributed by oxygen and light.
• Microorganisms grow on outside of casing but meat in casing get spoiled if
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• Less moisture: Molds produce fuzziness and discoloration
Sufficient moisture: Micrococci and yeast from slime layer
• Greening of sausage: Green ring formation from casing due to production of
peroxides e.g. hydrogen peroxide production by Lactobacillus and
Leuconostoc.
• Greening of sausages favored by slightly acidic pH and presence of small
amount of oxygen.
3. Hams
• Souring due to odors of mercaptane, hydrogen sulphide and amine etc.
• M/O involved are Psychrophilic halophiles, fecal Clostridium, fecal
Streptococci and Micrococci.
4. Refrigerated packaged meat
• Unwrapped meat or packaging films permitting good penetration of oxygen
and carbon di oxide favors more aerobic bacteria like Pseudomonas and
Moraxella (gram negative cocci) with production of Off flavor, slime and
putrefaction,
5. Canned meat
• Commercially sterile: Gas production and Putrefaction. M/O involved are
Bacillus sp. and Clostridium sp.
• Semi preserved canned meat: Souring, discoloration, putrefaction and gas
production. M/O involved are Streptococcus sp., Bacillus sp. and Clostridium
sp.
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