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Chapter 3
Sources of Microorganisms
in Foods
introduction
The internal tissues of healthy plants (fruits and vegetables) and animals (meat) are essentially sterile. Yet raw and processed (except sterile) foods contain different types of molds, yeasts, bacteria,
and viruses. Microorganisms get into foods from both natural (including internal) sources and
from external sources to which a food comes into contact from the time of production until the
time of consumption. Natural sources for foods of plant origin include the surfaces of fruits, vegetables, nuts, grains, and spices, and the damaged tissues and the pores in some tubers (e.g., radish
and onion). Natural sources for foods of animal origin include skin, hair, feathers, the gastrointestinal tract, the urogenital tract, the respiratory tract, and milk ducts (teat canal) in the udders of
milk animals. Natural microflora exist in ecological balance with their hosts, and their types and
levels vary greatly with the type of plants and animals as well as their geographical locations and
environmental conditions. Besides natural microorganisms, a food can be contaminated with different types of microorganisms coming from outside sources, such as air, soil, sewage, water, feed,
humans, food ingredients, equipment, packages, and insects. Microbial types and their levels from
these sources getting into foods vary widely and depend on the degree of sanitation used during
the handling of foods.
An understanding of the sources of microorganisms in food is important to develop methods
to control access of some microorganisms to the food, to develop processing methods to kill them
in food, and to determine the microbiological quality of food as well as to set up microbiological
standards and specifications of foods and food ingredients (Figure 3.1). The predominant types of
microorganisms that can get into food from each of these sources and methods to reduce the levels
of microorganisms are briefly discussed here.
Chapter 3
Sources of Microorganisms
in Foods
introduction
The internal tissues of healthy plants (fruits and vegetables) and animals (meat) are essentially sterile. Yet raw and processed (except sterile) foods contain different types of molds, yeasts, bacteria,
and viruses. Microorganisms get into foods from both natural (including internal) sources and
from external sources to which a food comes into contact from the time of production until the
time of consumption. Natural sources for foods of plant origin include the surfaces of fruits, vegetables, nuts, grains, and spices, and the damaged tissues and the pores in some tubers (e.g., radish
and onion). Natural sources for foods of animal origin include skin, hair, feathers, the gastrointestinal tract, the urogenital tract, the respiratory tract, and milk ducts (teat canal) in the udders of
milk animals. Natural microflora exist in ecological balance with their hosts, and their types and
levels vary greatly with the type of plants and animals as well as their geographical locations and
environmental conditions. Besides natural microorganisms, a food can be contaminated with different types of microorganisms coming from outside sources, such as air, soil, sewage, water, feed,
humans, food ingredients, equipment, packages, and insects. Microbial types and their levels from
these sources getting into foods vary widely and depend on the degree of sanitation used during
the handling of foods.
An understanding of the sources of microorganisms in food is important to develop methods
to control access of some microorganisms to the food, to develop processing methods to kill them
in food, and to determine the microbiological quality of food as well as to set up microbiological
standards and specifications of foods and food ingredients (Figure 3.1). The predominant types of
microorganisms that can get into food from each of these sources and methods to reduce the levels
of microorganisms are briefly discussed here.