Understanding Food
Chapter 7:
Food Preservation
Food Spoilage
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Biological Changes
Yeast: A fungus (a plant that lacks chlorophyll)
that is able to ferment sugars and that is used
for producing food products such as bread and
alcohol.
Fermentation: The conversion of carbohydrates
to carbon dioxide and alcohol by yeast or
bacteria.
Food Spoilage
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Chemical Changes
Chemical reactions or changes also contribute
to food deterioration.
Enzymes play a significant role in catalyzing
these reactions and can be categorized by the
substance on which they act (substrate) or their
mode of action. An example:
 Proteases, also called proteolytic enzymes,
split proteins into smaller compounds.
Food Spoilage
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Physical Changes
The most common physical changes occurring
in foods as they spoil are evaporation, drip loss,
and separation.
Dehydrate: To remove at least 95% of the water
from foods by the use of high temperatures.
Freeze-dry: To remove water from food when it
is in a frozen state, usually under a vacuum.
Food Preservation Methods
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Drying is the food
preservation process
that consists of
removing the food’s
water, which
effectively inhibits the
growth of
microorganisms. Like:
 Sun
Drying
Food Preservation Methods
Commercial Drying
 The most important types of commercial
drying are:
Conventional: heat.
Vacuum: pulls the water out.
Osmotic: water drawn out by osmosis.
Freeze-drying: ice crystals vaporize.
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Food Preservation Methods
Sublimation: The process in which a solid changes
directly to a vapor without passing through the liquid
phase.
Food Preservation Methods
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Cure: To preserve food through the use of salt
and drying. Sugar, spices, or nitrates may also
be added.
Fermentation
Pickling uses vinegar to preserve foods.
Edible coating: Thin layer of edible material
such as natural wax, oil, petroleum-based wax,
etc. that serves as a barrier to gas and moisture.
Food Preservation Methods
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Carbohydrates are required
for the fermentation
process.
Throughout Asia,
vegetables are still
commonly fermented.
In North America, foods
most often preserved by
fermentation are
cucumbers, olives, and
cabbage.
Food Preservation Methods
The purpose of edible coatings is fourfold:
1. To increase shelf life by acting as a barrier to moisture,
oxygen, carbon dioxide, volatile aromas, and other
compounds whose loss would lead to deterioration.
2. To impart improved handling characteristics, such as the
ability to bend more easily without breaking.
3. To improve appearance through increased gloss and
color.
4. To serve as a vehicle for added ingredients such as
flavors, antioxidants, antimicrobials, etc.
Food Preservation Methods
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Canning is a two-step process:
 First
the food is prepared by being packed into
containers, which are then sealed.
 Then
the containers are “canned,” or heated to
ensure that all microorganisms are destroyed.
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Sterilization: The elimination of all microorganisms
through extended boiling/heating to temperatures much
higher than boiling or through the use of certain
chemicals.
Pressure
cooker
Canner
Cold Preservation
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Refrigeration slows down the biological,
chemical, and physical reactions that shorten the
shelf life of food.
For safety purposes, refrigerators should be kept
between just above freezing to no more than
40°F (4°C).
All perishable foods should be refrigerated as
soon as possible, preferably during transport, to
prevent bacteria from multiplying.
Cold Preservation
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Freezing makes water unavailable to
microorganisms.
The chemical and physical reactions leading to
deterioration are slowed by freezing.
Rancid: The breakdown of the polyunsaturated
fatty acids in fats that results in disagreeable
odors and flavors.
Freezer burn: White or grayish patches on
frozen food caused by water evaporating into
the package’s air spaces.
Heat Preservation
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Pasteurization: A food
preservation process that
heats liquids to 160°F
(71°C) for 15 seconds, or
143°F (62°C) for 30
minutes, in order to kill
bacteria, yeasts, and
molds.