Chapter 2
Taxonomy, Role, and Significance
of Microorganisms in Foods
Because human food sources are of plant and animal origin, it is important to understand the
biological principles of the microbial biota associated with plants and animals in their natural habitats
and respective roles. Although it sometimes appears that microorganisms are trying to ruin our food
sources by infecting and destroying plants and animals, including humans, this is by no means their
primary role in nature. In our present view of life on this planet, the primary function of microorganisms
in nature is self-perpetuation. During this process, the heterotrophs and autotrophs carry out the
following general reaction:
All organic matter
(carbohydrates, proteins, lipids, etc.)
↓
Energy + Inorganic compounds
(nitrates, sulfates, etc.)
This, of course, is essentially nothing more than the operation of the nitrogen cycle and the cycle of
other elements. The microbial spoilage of foods may be viewed simply as an attempt by the food biota
to carry out what appears to be their primary role in nature. This should not be taken in the teleological
sense. In spite of their simplicity when compared to higher forms, microorganisms are capable of
carrying out many complex chemical reactions essential to their perpetuation. To do this, they must
obtain nutrients from organic matter, some of which constitutes our food supply.
If one considers the types of microorganisms associated with plant and animal foods in their natural
states, one can then predict the general types of microorganisms to be expected on this particular food
product at some later stage in its history. Results from many laboratories show that untreated foods
may be expected to contain varying numbers of bacteria, molds, or yeasts, and the question often arises
as to the safety of a given food product based on total microbial numbers. The question should be
twofold: What is the total number of microorganisms present per gram or milliliter and what types of
organisms are represented in this number? It is necessary to know which organisms are associated with
a particular food in its natural state and which of the organisms present are not normal for that particular
food. It is, therefore, of value to know the general distribution of bacteria in nature and the general
types of organisms normally present under given conditions where foods are grown and handled.
13
Taxonomy, Role, and Significance
of Microorganisms in Foods
Because human food sources are of plant and animal origin, it is important to understand the
biological principles of the microbial biota associated with plants and animals in their natural habitats
and respective roles. Although it sometimes appears that microorganisms are trying to ruin our food
sources by infecting and destroying plants and animals, including humans, this is by no means their
primary role in nature. In our present view of life on this planet, the primary function of microorganisms
in nature is self-perpetuation. During this process, the heterotrophs and autotrophs carry out the
following general reaction:
All organic matter
(carbohydrates, proteins, lipids, etc.)
↓
Energy + Inorganic compounds
(nitrates, sulfates, etc.)
This, of course, is essentially nothing more than the operation of the nitrogen cycle and the cycle of
other elements. The microbial spoilage of foods may be viewed simply as an attempt by the food biota
to carry out what appears to be their primary role in nature. This should not be taken in the teleological
sense. In spite of their simplicity when compared to higher forms, microorganisms are capable of
carrying out many complex chemical reactions essential to their perpetuation. To do this, they must
obtain nutrients from organic matter, some of which constitutes our food supply.
If one considers the types of microorganisms associated with plant and animal foods in their natural
states, one can then predict the general types of microorganisms to be expected on this particular food
product at some later stage in its history. Results from many laboratories show that untreated foods
may be expected to contain varying numbers of bacteria, molds, or yeasts, and the question often arises
as to the safety of a given food product based on total microbial numbers. The question should be
twofold: What is the total number of microorganisms present per gram or milliliter and what types of
organisms are represented in this number? It is necessary to know which organisms are associated with
a particular food in its natural state and which of the organisms present are not normal for that particular
food. It is, therefore, of value to know the general distribution of bacteria in nature and the general
types of organisms normally present under given conditions where foods are grown and handled.
13