This document discusses food spoilage, including signs, causes, and types of spoilage for various foods. It defines spoilage as the undesirable deterioration of food quality resulting in changes to odor, taste, and appearance. Spoilage can be caused by microbes like bacteria, yeasts, and molds or non-microbial factors. It provides examples of specific types of spoilage like putrefaction, fermentation, and rancidity that can occur. The document then examines spoilage of various food categories in more detail.

1. Spoilage of food products and causes
Spoilage Signs
Meat, Fish
Poultry
Dairy: Milk, Cheese etc.
Fruits
Vegetables
Canned Foods

2. Undesirable deterioration of food quality that may
result in changes in odor, taste and appearance of food.
The food becomes harmful to people and unsuitable for
consumption

3. Types of spoilage
Microbial:
Bacteria
yeasts
molds
Non-microbial:
Foreign materials
enzymes
Changes not necessarily harmful

4. Important definitions chemical Changes in Food
Putrefaction: (Anaerobic spoilage of proteins)
protein foods + proteolytic microorganisms  amino acids + amines +ammonia+ hydrogen sulfide
Proteolysis: is the breakdown of proteins into smaller polypeptides or amino acids.
In general, this occurs by the hydrolysis of the peptide bond, and is most commonly achieved by
cellular enzymes called proteases, but may also occur by intramolecular digestion, as well as by non-
enzymatic methods such as the action of mineral acids and heat
Fermentation: carbohydrate foods + saccharolytic microorganisms  acids + alcohols + gases
Rancidity: fatty foods + lipolytic microorganisms  fatty acids + glycerol
Browning of bananas: occurs because bananas contain an enzyme called polyphenol oxidase that
reacts with oxygen and coats the banana with a sort of rust that accounts for the dark brown color. This
enzyme is also found in apples, potatoes and pears

5. SPOILAGE OF MEAT
Important reasons -Low redox potential value because meat is rich in aa Cysteine Therefore, spoilage by aerobic
and anaerobic m/os’ occur only on surface. Deeper parts are spoilt by anaerobic m/o’s or facultative aerobes.
Food Types of Spoilage Spoilage Microorganisms
MEAT
Fresh
Putrefaction
Clostridium, Pseudomonas, Proteus, Alcaligenes,
Chromobacterium
Souring Chromobacterium, Lactobacillus, Pseudomonas
Cured
Mouldy Penicillium, Aspergillus, Rhizopus
Souring Pseudomonas, Micrococcus, Bacillus
Greening Lactobacillus spp., Streptococcus, Pediococcus
Slimy Leuconostoc
Vacuum
Packed
Souring
Greening
Lactobacillus, Carnobacterium, Leuconostoc
Poultry Odor, Slime
Pseudomonas, Alcaligenes, Xanthomonas

6. • Brown or grey discoloration - Protein denaturation caused by heat, salts, ultraviolet light, low pH, and
surface dehydration
• The pigment myoglobin which determines the color of fresh meat undergoes various chemical reactions
to form other pigments.
• The microbes change the physiological environment by changing the pH and by producing amino acids
and amines.
• They may also produce compounds which may react with the heme pigments to produce other colors.
Catalase negative bacteria produce hydrogen peroxide that results in a green color.
• Microorganisms change the color also by producing pigments themselves.
• Cooking causes protein denaturation and the browning reactions. During cooking the heme pigment
protein denatures and the iron undergoes oxidation to the ferric state and ability of the pigment to
complex oxygen is lost.

7. Spoilage of Meat ( Anaerobic Conditions)
• Souring: production of volatile organic acids. Clostridium sp, some lactic acid
bacteria cause it.
• Putrefaction: Caused by proteolytic sp. Of clostridia eg. C. sporogenes, C.
botulinum and C. putrfaciens.
• Degrade meat under anaerobic conditions producing fowl smelling
compounds s.a. ammonia, mercaptone, indole, skatole.
• Taint: Off-odour and Off taste
• Gassiness of meat: due to production of various gases under anaerobic
conditions esp. CO2 and H2.

8. Spoilage of Fish
Food Types of Spoilage Spoilage Microorganisms
FISH
Discoloration Pseudomonas
Putrefaction
Chromobacterium,
Halobacterium, Micrococcus
EGGS
Green rot Pseudomonas
Colorless rot
Pseudomonas, Alcaligenes,
Chromobacterium
Black rot Coliforms
Fungal rot Proteus, Penicillium, Mucor

9. SPOILAGE OF poultry
Green Rot of Eggs: Ps. Fluorescens- egg emits green color fluorescence under uv light.
Colorless rot of eggs: Alcaligenes, Acinetobacter, Pseudomonas. The egg white develops a white
crusty
precipitate and later yolk sac also develops crusty ppt. This is visible after breaking the eggs.
Black Rot of Egg: Proteus, Pseudomonas, Aeromonas. Occurs at room temp.—yolk sac develops
black brown discoloration due to H2S production and deposition.
Pink Rot of eggs: Pseudomonas vulgaris
Red Rot of Eggs: Serratia sp…mild ammonical smell
Mustiness of egg: Musty off odor---Ps. Graveolens, Proteus sp

10. Milk and product spoilage
Reasons for highly perishable food
pH b/w 6.3-6.5
High Moisture
Rich Nutrients
(lactose sugar,
butterfat, citrate
and nitrogenous
compounds
Free aa: Casein and Lactalbumin-rich N-
source
Lactose sugar-simple, fermentable
Milk fat hydrolysed by microbial lipases
(butyric, capric and caproic acid)

11. Food Types of Spoilage Spoilage Microorganisms
DAIRY
MILK
(pasteurized)
Bitterness Pseudomonas spp.
Souring Lactobacillus thermophilus
Sweet curdling Bacillus cereus
CHEESE
Green discoloration Penicillium
Green to black
discoloration
Cladosporium
Black discoloration Candida
Sliminess (high pH) Pseudomonas spp.
“Gassy” cheese Coliforms, LAB, Clostridia

12. Changes in Milk Fat
Alkali Production
Flavor Changes
Sour or acid flavor: Clean acid flavor, Aromatic acid flavor, Sharp acid flavor
Bitter flavor- Proteolysis of casein (Bacillus sp., Clostridium)
Burnt/Caramel flavor (burnt milk flavor-S. lactis var. maltigenes)
Color Changes
Blue milk (Ps. syncyannea)
Yellow milk (Ps. Synxantha, Flavobacterium)
Red milk (Serratia marcesans, Torula glutinis)
Brown milk (Ps. putrfaciens)

13. Gas production: accompanied by acid formn- mainly by coliform bacteria, Clostridium and gas-forming Bacillus sp.- yield
H2 and CO2
Production of gas seen as foam on the top if milk is liquid and super saturated with gas bubbles caught in curd, floating
curd-ripping apart of curd by rapid gas producn- Stormy fermentation of milk.
Heterofermentative lactics (non-coliforms) may produce gas not enough to be evidenced.
Yeast (lactose-fermenting) usually absent/low no.- cannot compete out bacteria.
Acid formers killed at pasteurization temps.- however spores of clostridium and bacillus may survive and cause spoilage
of pasteurized milk.

14. Why
Spoilage of
Fruits and
Vegetables?
20% food fruits and Vegetables spoilt by m/o
High moisture content , good source of vitamins
Composition:
Water 88%
Carbohydrates 8.6%
Proteins 1.9%
Fat 0.3%
Ash 0.84%
pH >5.3
High Eh
Spoilt by Aerobes and Fac. anaerobes

15. Food
Types of
Spoilage
Spoilage Microorganisms
FRESH FRUITS
AND
VEGETABLES
Bacterial soft rot Erwinia carotovera, Pseudomonas spp.
Gray mould rot Botryitis cinerea
Rhizopus soft rot Rhizopus nigrican
Blue mould rot Penicillium italicum
Black mould rot Aspergillus niger, Alternaria
Sliminess and
Souring
Saprophytic bacteria

16. SPOILAGE OF BEER
• 4 diff. types of beer infections:
• Ropiness of beer- Beer becomes viscous due to bacterial growth-
Aceto bacter, Lactobacillus, Pediococcus
• Sarcinae sickness – Pediococcus cerevisae produces diacetyl which
when combined with normal odor of beer imparts characteristic
odor to beer
• Souring of beer – due to growth of acetobacter. It oxidises ethanol
in beer to acetic acid
• Turbidity and Off-flavor in beer- Growth of unwanted bac. and
yeasts. (Pediococcus cerevisae, Saccharomyces pasteurianum)

17. Spoilage of Butter
Butter not easily spoilt by m/os
• Contains Min. 80% fats-spoilt only by lipophillic m/o’s
• Stored at v. low temp-spoilt only by psychrophiles
• Contains only 15% water-low aw
• Contains antimicrobial substances like Diacetyl (produced naturally).
• Usually salted
• Wrapper of butter impregnated with sodium diacetyl (chemical preservative)

18. SPOILAGE OF CANNED FOODS
• An ‘Unspoilt Can’ usually has a flat or slightly concave ends.
• The appearance of an unspoilt can gives an idea if food inside is spoilt
or not.
Important
Flipper- both ends flat, when strike end of can sharply, one end of can
will become convex.
• Springer- one end is flat, other end bulged out. On pressing the bulged end,
other end bulges out.

19. SPOILAGE OF CANNED FOODS
• Soft swell-both ends of unopened can are bulged out but pressure of the gas
inside is not too much. Therefore both ends can be pressed inwards
• Hard swell – both ends of unopened can are bulged out, pressure of gas
inside too much- cannot be pressed
• First two types of can-food either not spoilt or spoilage just started.
• Last two- spoilage has taken place.