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Food spoilage
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Food Spoilage:
Nearly one-fourth of the worlds food
supply is lost as a result of microbial
spoilage.All foods undergo deterioration after
harvest to some degree
Role of food sciences is to minimize
negative changes
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Shelf life:
The time during which the food product will:
Remain safe (safety).
Be certain to retain desired sensory, chemical,physical and microbiological characteristics
(spoilage).
Comply with any label declaration ofnutritional data.
When stored under the recommended
conditions
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Food Spoilage
Any changes in a food that renders it
unacceptable or unsafe for human
consumption.These changes depends on :
food item
processing method
packaging
storage conditions
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Major Causes of Food Spoilage
Growth & activity of microorganisms bacteria
yeast
molds
Activity of food enzymes
Infestation by: insects
parasites
rodents
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Inappropriate temperatures
during processing
during storageGain or loss of moisture
Reaction with oxygen
LightPhysical stress or abuse
Major Causes of Food Spoilage
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Types of M.O found in food
1. Spoilage MO (Spoilage)
2. Pathogenic MO (Safety)
3. Fermentative MO (Processing)
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Bacteria
Bacteria single-celled Round (cocci)
Rod-shaped (bacilli)
Some produce spores
dormant condition resistant to
heat, chemicals, and other
adverse conditions
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Mold
Larger than bacteria
Are often filamentous
All produce spores
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Yeast
Largest of the microorganisms
Single cells
Some produce spores
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Foods are classified according to their
susceptibility to microbial spoilage to:
1-Perishable foods:
Meat, fish, poultry, and most fruits and
vegetables, egg and milk2-Semi-perishable foods:
Potatoes and apples
3-Non-perishable foods:Cereals, grain, dry products, sugar, flour
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Putrefaction
M.O produce extra-cellularprotease orprotease or
proteinasesproteinases enzymes.
These enzymes hydrolyze a variety of proteinscausing spoilage
(odor, flavor and textural changes)
Pseudomonas spp is highly proteolytic and is
capable of degrading milk protein (casein)
resulting in coagulation and spoilage.
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Hydrolytic rancidity
M. O that produce extra-cellularlipases
triglycerides glycerol + FFA
milk, cream, butter, cheese, sausages
FFA especially the short chained (C3 to C6) are
very volatile.
The FFA may be further oxidized to aldehydes
and ketones giving rise to further flavor / odor
compounds.
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2- SLIMINESS:
Food becomes slimy as the bacterialpopulation grows
Synthesis of polysaccharides that formsa sticky layer on the surface.
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3- DISCOLOURATION
Foods can become discolored by microbial
growth.
Some molds have colored spores that givethe food a distinctive color
Black pin mold on bread, or blue and
green mold on citrus fruit and cheese.Green discoloration of processed red meat
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4- SOURING:
Foods become sour when certainbacteria produce acids.
A common example is when milk soursfrom the production of lactic acid.
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5- GAS:Bacteria and yeasts often produce gaseous
by-products
Packages and cans swelling
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Sequence of microbial spoilage
M.O have to get into food (type and number)
Food environment must support the growth of
Contaminated M.O(pH, aw , ORP, nutrients, .)
Food must be stored (abused) at temperatureenable M.O to multiply
Food must be stored for sufficient length of time
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Specific spoilage microorganisms:
M.O which can grow and cause spoilage
under the storage conditions
Food Spoilage:
1. 107 cfu/ g or ml or cm2 normally results in
odor problems2. 107 to 108 cfu per g or ml or cm2 usually
results in foods having surface slime and
odor