Section III. MAJOR CAUSES OF FOOD DETERIORATION
1-5.
INTRODUCTION
The point that foods do deteriorate has been adequately made; but what are the
causes of food deterioration? There are six major causes of food deterioration--
microorganisms, action of enzymes, chemical reactions, physical changes, time, and
insects and/or rodents. These causes are not isolated in nature. Bacteria, insects, and
light, for example, can all be operating simultaneously to deteriorate food in the field or
in a warehouse. Similarly, such causes as high temperature, moisture, and air will all
affect the multiplication and activities of bacteria, as well as the chemical and enzymatic
activities of the food. At any one time, many forms of deterioration may be in progress,
depending upon the food and environmental conditions. Total food preservation, an
ideal that can only be approached, requires that we eliminate or minimize all of these
causes that may affect a susceptible food.
1-6.
MICROORGANISMS
The microorganisms that are principally involved in food deterioration are
bacteria, molds, and yeasts. There are thousands of genera and species of
microorganisms. Several hundred are associated in one way or another with food
products. Not all cause food spoilage, and many types are used in preserving foods,
such as the lactic-acid-producing organisms of cheese, sauerkraut, and some types of
sausage. Other microorganisms are used for alcohol production as in wine or beer-
making, or for flavor production in other foods. However, except where these
microorganisms are especially cultivated by selective inoculation or by controlled
conditions to flavor their growth over that of less desirable types, microorganism
multiplication on or in foods is a major cause of food deterioration. The microorganisms
will attack virtually all food constituents. Some will ferment sugars and hydrolyze
starches and cellulose. Others will hydrolyze fats and produce rancidity. Still others will
digest proteins and produce putrid and ammonia-like odors. Some will form acid and
make food sour. Others will produce gas and make food foamy. Some will form
pigments, and a few will produce toxins and give rise to foodborne illnesses. When
food is contaminated under natural conditions, several types of organisms will be
present together. Such mixed organisms contribute to a complex of simultaneous or
sequential changes which may include acid, gas, putrefaction, and discoloration.
a. Bacteria. Bacteria are unicellular microorganisms of many forms, although
three principal shapes of the individual cells predominate. These are the spherical
shape represented by several forms of cocci, the rod shape of the bacilli, and spiral
forms possessed by the spirilla. Some bacteria produce spores which are remarkably
resistant to heat, chemicals, and other adverse conditions. Bacterial spores are far
more resistant than yeast or mold spores, and more resistant to most processing
conditions than natural food enzymes. All bacteria associated with foods are small.
Most are of the order of one to a few microns in cell length and somewhat smaller than
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