(2) Cold damage. Cold damage to foods does not necessarily require the
extreme of freezing. Many fruits and vegetables, like other living systems, have
optimum temperature requirements after harvest. Held at common refrigeration
temperatures of about 41F (5C), several fruits and vegetables are weakened or
killed and deteriorative processes follow. The deteriorations include off-color
development, surface pitting, and various forms of decay. Bananas, lemons, squash,
and tomatoes are examples of products that should be held at temperatures no lower
than 50F (10C) for maximum quality retention. This provides an exception to the
inaccurate generalization that cold storage preserves all foods, and the colder the
b. High Temperature. There is a moderate temperature range over which
much food is handled, such as 50-100F (10-38C). Within this range, for every 18F
(10C) rise in temperature, the rate of chemical reaction is approximately doubled. This
includes the rates of many enzymatic as well as nonenzymatic reactions. Excessive
heat can denature proteins, break emulsions, dry out foods by removing moisture, and
(1) Effect on vegetables. Excessive heat in green vegetables causes cell
walls and membranes to lose their integrity and acids and enzymes to be released. All
of these result in the development of a soft texture as well as the development of off-
colors and off-flavors.
(2) Effect on muscle tissue. The consequences of excessive heat on
muscle tissue are that proteins are denatured, the proteins clump together, and
enzymes are inactivated. This results in a toughening of the texture, loss of water-
holding capacity, cooked or caramel flavors, and development of off-colors.
c. Dehydration. Dehydration, another form of physical change that causes food
deterioration, can be simply defined as the loss of water from the food product. Foods,
especially fresh, chilled, and frozen, are subject to dehydration.
(1) Amount of water in food. Foods contain a substantial amount of water.
Meat products contain from 70 to 75 percent water, whereas fresh fruits and vegetables
contain from 80 to 95 percent water. Since water vapor is continually seeking to go
from an area of high concentration to an area of low concentration, improper storage
conditions and improper packaging will result in dehydration. When the humidity is too
low in a storage area, dehydration results.
(2) Signs of dehydration. The signs of dehydration include dryness or
shriveling on the surface of the food item. The development of off-colors, usually a
darkening effect, will also be observed.
(3) Terms used. In frozen foods, the dehydration is known as freezer burn.
In fresh fruits and vegetables, it is known as wilt.