Transcript Spoiled

Food Spoilage
What is Food Spoilage
Spoilage is a natural phenomenon.
It occurs at varying rates depending
on the storage temperature, kind of
food involved, kind of microorganisms present, packaging materials
used, food additives used and
method of preservation.
Spoiled Food can be defined as
any food that is not acceptable to
an individual or group because of
health hazard or aesthetic appeal.
The period of time between the manufacture
and the retail purchase of food is called the
Shelf Life.
During this time a food product has a
satisfactory quality in terms of nutritional
value, taste, texture and appearance
Food categories
Stable or Nonperishable Foods
Semi-perishable Foods
Perishable Foods
PRE-HARVEST DETERIORATION
10-20% AGRICULTURAL COMMODITIES ARE LOST
•WEEDS
•INSECTS
•MICROORGANISMS
•RODENTS
•BIRDS
Conditions Leading to Food
Decay
EXTERNAL CONDITIONS
Storage temperature
Humidity
Gas O2, N2, CO2
Packaging materials
Light
BIOCHEMICAL/CHEMICAL DECAY
Rancidity
WOF
Changes in texture
PRODUCT CONDITIONS
Initial quality
Raw material
Ingredients
Intrinsic factors
Hygienic Processing
MICROBIAL DECAY
Putrid flavor
Sour taste
Slime, Gas
Discoloration
Off-flavors
Loss od nutrients
Formation od toxic substances
Changes in texture
Causes of Food Spoilage:
 Senescence
 Microbial decay
 Chemical deterioration (enzymatic &
non-enzymatic)
 Physical deterioration; desiccation.
 Insects and rodents
SENESCENCE
•FRUITS & VEGETABLES CONTINUE TO
RESPIRE AFTER HARVEST LEADING TO
DETERIORATION
•CATABOLIC REACTIONS IN MEAT & FISH
Enzymatic spoilage
Enzymes are chemicals produced by all living
things. They help speed up or slow down
chemical reactions, act as transports for
foods, and are a normal constituent of foods.
For instance, as a banana matures, the color
changes from green to yellow to brown to
black. The change is caused by the enzymes
(chemicals) in the banana.
The ripening, then softening, of other fruits
such as apples, peaches and tomatoes is
another example of enzymatic action.
Enzymatic spoilage
Enzymes can be inactivated by heat, which is the
reason for blanching vegetables; or they can be
inactivated by cold temperatures below 40 degrees
F, which is the reason for placing vegetables under
refrigeration. Think of green tomatoes in the
refrigerator compared to tomatoes sitting on the
window sill.
Bacteria also produce enzymes that break
down food and allow them to obtain
nutrients through their cell walls. Therefore,
lowering the temperature reduces the rate of
enzyme action as well as the rate at which
bacteria can multiply.
Examples:
 In corn and pea:
simple sugar
starch
 In vegetables and fruits
phenol + O2
brown products
 In butter
fat
hydrolysed fat
Physical Deterioration &
Dessication
• PHYSICAL/MECHANICAL ABUSE CAUSES
RELEASE OF ENZYMES INTO TISSUES
• CRUSHING, BREAKS IN THE SKIN (FRUIT/
VEGETABLE) LEAD TO MICROBIAL INVASION
• WATER/MOISTURE LOSS DURING STORAGE
• WATER/MOISTURE UPTAKE
• RETROGRADATION OF STARCH
• MELTING OF FOOD
Microbial Decay
Bacteria
Yeasts
Molds
Viruses
BACTERIA
• GROW THE FASTEST
• REPRODUCE BY CELL DIVISION:
• VEGETATIVE CELLS (actively metabolizing cells,
consume nutrients and produce waste products)
• SPORES (dormant form of the bacterial cell)
• BASIC SHAPES:
• COCCI (CIRCULAR SHAPE)
• RODS (LENGTH IS GREATER THEN WIDTH)
• MOTILE RODS (FLAGELLA)
Yeasts ; Molds
YEASTS
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COMMONLY FOUND IN MANY FOODS
GROWTH IS SLOWER
TOLERATE SEVERE ENVIRONMENTAL CONDITIONS (pH, aw)
SOME ARE USED TO PRODUCE FERMENTED FOODS
MOLDS
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FILAMENTOUS FORM
FOUND IN MOST FOODS
TOLERATE HARSH ENVIRONMENTAL CONDITIONS
SOME USED IN FERMENTED FOODS
AGENTS OF FOOD SPOILAGE
PRODUCE TOXINS (MYCOTOXINS)
PRODUCE SPORES
(pH, aw)
MICROORGANISMS CAN BE CHARACTERIZED ON THE
BASIS OF OXYGEN REQUIREMENTS
AEROBES
GROW ONLY IN THE PRESENCE OF O2
ANAEROBES
GROW ONLY IN THE ABSENCE OFO2
FACULTATIVE ANAEROBE
CAN GROW IN THE PRESENCE/ABSENCE OF O2
BACTERIA: Aerobes, anaerobes, facultative anaerobes
YEASTS are facultative anaerobes
MOLDS are strictly aerobes
Conditions Necessary for Microbial
Decay
Microbial spoilage is the major cause of food spoilage.
It occurs as a result of contamination of food by
microorganisms, provision of a suitable environment for their
growth, and degradation of the foodstuffs.
To control microbial build up, you must control:
• The source of microorganisms - people, raw materials,
equipment, air currents, dust and pests.
• Food residues, which are required for bacterial growth
Conditions Necessary for Microbial
Decay
• Moisture is required for growth; thus
relative humidity should be monitored.
• Time during which food product is
exposed to a given set of conditions that
promote bacterial growth.
• Temperature determines the kind of
microorganisms.
Microbial Growth Curve
A-B lag phase
B-C phase of positive
acceleration
C-D exponential phase
D-E phase of negative
acceleration
E-F stationary phase
F-G accelerated death
phase
G-H death phase
H-I survival phase
The best way to prevent microbial
food decay is to lengthen:
The lag phase
The phase of positive growth
This can be accomplish by:
Reducing the amount of microbial
contamination as much as possible
Avoiding the addition of actively growing
organisms
Microbial decay can be prevented by:
Keeping out microorganisms
Removal of microorganisms
Hindering the growth or activity of
microorganisms
Killing the microorganisms
Self-decomposition of food can be
prevented by:
by destruction or inactivation of
food enzymes
by prevention or delay of purely
chemical reactions
Classification of food preservation methods based
on major controlling factors
high temperature
low temperature
removal or tying up moisture
addition of chemical preservatives
keeping microorganisms out
ionizing radiation (irradiation)
The kinds and numbers of microorganisms
present on or in food depends on:
The kind and extent of contamination
Previous opportunities for the growth of
certain kinds
Pre-treatments which food has received
Factors affecting microbial growth
Associative Growth: Antibiotic, Symbiotic,
Metabiotic
Environmental Conditions:
Physical State of Food
Chemical State of Food
Temperature
Chemical Changes caused
by microorganisms:
Changes in nitrogenous organic
compounds.
Anaerobic decomposition of proteins,
peptides and amino acids that result in
production of obnoxious odorous is called
Putrefaction.
Changes in carbohydrates:
Alcoholic fermentation
Lactic fermentation
Mixed lactic fermentation
Coliform type fermentation
Propionic fermentation
Butyric-butyl-isopropyl fermentation
Changes in organic acids
 Changes in lipids
 Other changes