3. Food Spoilage

7/31/2019 3. Food Spoilage

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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
http://en.wikipedia.org/wiki/Image:Moldy_nectarines.jpg


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Yeast

Largest of the microorganisms

Single cells

Some produce spores
http://en.wikipedia.org/wiki/Image:S_cerevisiae_under_DIC_microscopy.jpg


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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

3. Food Spoilage

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