120 ◾ Fundamental Food Microbiology
utilize some components present in the raw materials as substrates to generate energy and cellular components, to increase in population, and to produce many usable byproducts (also
called end products) that are excreted in the environment. The unused components of the raw
materials and the microbial byproducts (and sometimes microbial cells) together constitute fermented foods. The raw materials can be milk, meat, fish, vegetables, fruits, cereal grains, seeds,
and beans, fermented individually or in combination. Worldwide, more than 3500 types of
fermented foods are produced. Many ethnic types are produced and used in small localities by
small groups of people. Many of the fermented foods consumed currently have been produced
and consumed by humans for thousands of years. The old city civilizations, dating as far back
as 3000 b.c.–5000 b.c. in the Indus Valley, Mesopotamia, and Egypt, developed exceptional
skills in the production of fermented foods from milk, fruits, cereal grains, and vegetables. The
process not only produced new foods but also helped preserve the excess of raw materials both
of plant and animal origins. 1
The basic principles developed by these ancient civilizations are used even today to produce
many types of fermented foods by a process known as natural fermentation. In this method, either
the desirable microbial population naturally present in the raw materials or some products containing the desirable microbes from a previous fermentation (called back slopping), are added to the
raw materials. Then the fermentation conditions are set so as to favor growth of the desirable types
but prevent or retard growth of undesirable types that could be present in the raw materials. In
another type of fermentation, called controlled or pure culture fermentation, the microorganisms
associated with fermentation of a food are first purified from the food, identified, and maintained
in the laboratory. When required for the fermentation of a specific food, the microbial species
associated with this fermentation are grown in large volume in the laboratory and then added to
the raw materials in very high numbers. Then the fermentation conditions are set such that these
microorganisms grow preferentially to produce a desired product. Characteristics of some of the
microorganisms used in fermentations are discussed here. These microbial species, when used in
controlled fermentation, are also referred to as starter cultures. Many of these microbial species are
present in raw materials that are naturally fermented along with other associated microorganisms,
some of which may contribute to the desirable characteristics of the products.
Lactic Starter Cultures 2,3
At present, bacterial species from 12 genera are included in a group designated as lactic acid bacteria
because of their ability to metabolize relatively large amounts of lactic acids from carbohydrates. 4,5
The genera include Lactococcus, Leuconostoc, Pediococcus, Streptococcus, Lactobacillus, Enterococcus,
Aerococcus, Vagococcus, Tetragenococcus, Carnobacterium, Weissella, and Oenococcus. Many of the
genera have been created recently from previously existing genera and include one or a few species.
For example, Lactococcus and Enterococcus were previously classified as Streptococcus Group N and
Group D, respectively. Vagococcus is indistinguishable from Lactococcus, except that these bacteria
are motile. Weissella and Oenococcus are separated from Leuconostoc. Tetragenococcus includes a single species that was previously included with Pediococcus (Pediococcus halophilus). Carnobacterium
was created to include a few species that were previously in genus Lactobacillus and were obligatory
heterofermentative. However, species from the first five genera, that is, Lactococcus, Leuconostoc,
Pediococcus, Streptococcus, and Lactobacillus, are used as starter cultures in food fermentation and
are discussed here. The status of others, except Tetragenococcus halophilus and Oenococcus oeni,
with respect to use in food, is not clear at present.
utilize some components present in the raw materials as substrates to generate energy and cellular components, to increase in population, and to produce many usable byproducts (also
called end products) that are excreted in the environment. The unused components of the raw
materials and the microbial byproducts (and sometimes microbial cells) together constitute fermented foods. The raw materials can be milk, meat, fish, vegetables, fruits, cereal grains, seeds,
and beans, fermented individually or in combination. Worldwide, more than 3500 types of
fermented foods are produced. Many ethnic types are produced and used in small localities by
small groups of people. Many of the fermented foods consumed currently have been produced
and consumed by humans for thousands of years. The old city civilizations, dating as far back
as 3000 b.c.–5000 b.c. in the Indus Valley, Mesopotamia, and Egypt, developed exceptional
skills in the production of fermented foods from milk, fruits, cereal grains, and vegetables. The
process not only produced new foods but also helped preserve the excess of raw materials both
of plant and animal origins. 1
The basic principles developed by these ancient civilizations are used even today to produce
many types of fermented foods by a process known as natural fermentation. In this method, either
the desirable microbial population naturally present in the raw materials or some products containing the desirable microbes from a previous fermentation (called back slopping), are added to the
raw materials. Then the fermentation conditions are set so as to favor growth of the desirable types
but prevent or retard growth of undesirable types that could be present in the raw materials. In
another type of fermentation, called controlled or pure culture fermentation, the microorganisms
associated with fermentation of a food are first purified from the food, identified, and maintained
in the laboratory. When required for the fermentation of a specific food, the microbial species
associated with this fermentation are grown in large volume in the laboratory and then added to
the raw materials in very high numbers. Then the fermentation conditions are set such that these
microorganisms grow preferentially to produce a desired product. Characteristics of some of the
microorganisms used in fermentations are discussed here. These microbial species, when used in
controlled fermentation, are also referred to as starter cultures. Many of these microbial species are
present in raw materials that are naturally fermented along with other associated microorganisms,
some of which may contribute to the desirable characteristics of the products.
Lactic Starter Cultures 2,3
At present, bacterial species from 12 genera are included in a group designated as lactic acid bacteria
because of their ability to metabolize relatively large amounts of lactic acids from carbohydrates. 4,5
The genera include Lactococcus, Leuconostoc, Pediococcus, Streptococcus, Lactobacillus, Enterococcus,
Aerococcus, Vagococcus, Tetragenococcus, Carnobacterium, Weissella, and Oenococcus. Many of the
genera have been created recently from previously existing genera and include one or a few species.
For example, Lactococcus and Enterococcus were previously classified as Streptococcus Group N and
Group D, respectively. Vagococcus is indistinguishable from Lactococcus, except that these bacteria
are motile. Weissella and Oenococcus are separated from Leuconostoc. Tetragenococcus includes a single species that was previously included with Pediococcus (Pediococcus halophilus). Carnobacterium
was created to include a few species that were previously in genus Lactobacillus and were obligatory
heterofermentative. However, species from the first five genera, that is, Lactococcus, Leuconostoc,
Pediococcus, Streptococcus, and Lactobacillus, are used as starter cultures in food fermentation and
are discussed here. The status of others, except Tetragenococcus halophilus and Oenococcus oeni,
with respect to use in food, is not clear at present.