Food Preservation and Processing
Preservation Methods
As consumers look for convenient foods to feed their families, food processors seek new
methods of food preservation and packaging to meet the demand. Some of the methods
used by commercial processors are similar to those used by consumers to keep food safe,
but food scientists are always looking for new ways to control the food environment to
maintain freshness and flavor and prohibit microbial growth. Following is a list of some
common methods used to preserve and process food:
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•Applying heat: Cooking procedures soften food for chewing, increase food
palatability, and prepare food for digestion. Heat is also an important means of
ensuring food safety in home and industrial processing. Most bacteria are killed at
temperatures of 180° to 200° F.55 Heat also inactivates enzymes that promote the
deterioration of fruits and vegetables. This is why vegetables are first blanched in
boiling water to prevent further enzyme activity before being frozen.
Pasteurization is a means of eliminating pathogens in fluid milk and fruit juices.
Canned foods are exposed to temperatures that effectively sterilize the food
contents. Foods canned at home at too low a temperature carry the risk of
botulism (see preceding section on foodborne illness).
•Keeping food cold: Microbial activity slows at temperatures less than 50° F; thus
refrigeration at 45° F or lower will preserve food for a limited period of time.55
Freezing prevents microbial growth; however, bacteria remain alive, although
dormant. Therefore it is important not to refreeze food that has been thawed for
some time, allowing microorganisms to begin to multiply. Cold temperatures will
decrease but not eliminate enzyme activity.
•Removing moisture: Drying lowers the water activity in a food, removing
available water and thus preventing survival and growth of any microorganism
present. Foods dried at high temperatures, such as ready-to-eat cereals, and
freeze-dried foods retain more flavor and color. The removal of water from a food
also slows enzyme activity and destructive oxidation reactions.
•Adding acid, sugar, salt, or chemical additives: Acid-containing foods lower in
pH are more resistant to the growth of bacteria. Before the era of refrigeration,
fermentation with the production of acid was used to turn perishable milk into
yogurt or cheese that could be safely stored for a longer time. Adding salt or sugar
to a food controls the growth of bacteria by limiting the available water to existing
microorganisms. In this way the high sugar content of jams prevents spoilage. In
earlier times, salt curing was a means of preserving meat, and pickling is still used
by home and commercial food processors. Chemical additives such as sodium
benzoate or calcium propionate are added to bread and grain products to retard the
growth of bacteria and mold and increase shelf life.
TABLE 9-3 Examples of Food Additives
Type
Chemical Compound
Function
Used to keep food
dry and prevent
Anticaking
Calcium silicate,
caking as moisture is
agent
calcium stearate
absorbed from the
air; keep item freeflowing
Antimicrobial Calcium propionate,
Prevent growth of
agent
sodium propionate
mold
Prevents oxidation
Butylated
reactions and
hydroxyanisole
Antioxidants
rancidity in
(BHA), butylated
unsaturated fatty
hydroxytoluene (BHT)
acids
Common Food
Uses
Table salt,
powdered sugar,
baking powder
Bread
Vegetable oils,
potato chips
Freshly milled
wheat flour, white
Bleaching
Chlorine, benzoyl
Whiten appearance flour for allagent
peroxide
purpose use or
cakes
Acts with an acid in Double-acting
Chemical
a batter to release
baking powder for
leavening
Sodium bicarbonate
carbon dioxide (CO2) quick breads,
systems
for leavening
cakes, and cookies
Margarine, candy,
Annatto (natural),
Make color of food carbonated
Coloring agent FD&C red #3, FD&C
items more appealing beverages and fruit
yellow #5 (artificial)
drinks
Dough
Ammonium chloride,
Improves volume
Bread
conditioners
calcium phosphate
Keeps the waterLecithin,
soluble and fatMargarine, cake
Emulsifier
monoglycerides and
soluble ingredients
mixes
diglycerides
evenly distributed
throughout a food
Retain moisture,
Soft cookies, cake
Propylene glycol,
prevent food from
frosting,
Humectants
sorbitol
becoming hard or
marshmallow
stiff
candy
Amyl acetate, methyl
Flavoring
salicylate, essential
Enhance flavor or
Most processed
agents
oils, monosodium
aroma of foods
foods
glutamate (MSG), salt
Common Food
Uses
Preserves pink color Processed meats
Sodium nitrate (color)
in cured meats,
such as
Preservative
Sodium nitrite (food
prevents rancidity in frankfurters,
safety)
meats and botulism canned foods
Binds with metals
such as iron or
Wine, juice,
Sequestrant
Citric acid
copper to prevent
mayonnaise
changes in flavor,
color, or appearance
Maintain appropriate
Pectin, locust bean
food texture and
Stabilizers and
Jelly, ice cream,
gum, guar gum,
mouth feel;
thickeners
pudding, yogurt
carrageenan
thickener, absorb
water
Type
Chemical Compound
Function
•Changing the atmosphere: A new method of food preservation involves changing the
atmosphere—that is, removing the oxygen necessary for bacterial growth and enzyme
activity and replacing it with carbon dioxide (CO2) or nitrogen, which slows these
activities. Modified atmosphere packaging is used for highly perishable foods such as
ready-to-eat chicken pieces and salad mixes.
Williams' Essentials of Nutrition and Diet Therapy, 10th Edition
CH. 9, P.208