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Understanding Food
Chapter 7:
Food Preservation
Food Spoilage
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
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
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
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.
Food Preservation Methods
Sublimation: The process in which a solid changes
directly to a vapor without passing through the liquid
phase.
Food Preservation Methods
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
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
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.
Sterilization: The elimination of all microorganisms
through extended boiling/heating to temperatures much
higher than boiling or through the use of certain
chemicals.
Pressure
cookerCanner
Cold Preservation
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
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
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.
