Characteristics of Predominant Microorganisms in Food ◾ 27
Propionibacterium. Pleomorphic rods (0.5 × 2 μm); can be coccoid, bifid, or branched; present
singly or in short chains; V and Y configuration and in clumps with Chinese-character-like
arrangement; nonmotile; anaerobes; mesophiles. Dairy propionibacteria are used in food
fermentation (Propionibacterium freudenreichii in Swiss cheese). Produce proline and propionic acid. Found in raw milk, Swiss cheese, and silage.
Some New Genera
On the basis of nucleic acid homology studies, several new genera have been created from the existing
genera. Some that are important in food microbiology are listed here. Most of their characteristics are
similar to those of the species in the respective old genera. Examples include Tetragenococcus (from
Pediococcus), Vagococcus (from N-group Streptococcus), Weissella and Oenococcus (both from Leuconostoc),
Kocuria (from Micrococcus), Shewanella (from Pseudomonas), and Alicyclobacillus (from Bacillus).
important Bacterial Groups in Foods
Among the microorganisms found in foods, bacteria constitute major important groups. This is
not only because many different species can be present in foods, but also because of their rapid
growth rate, ability to utilize food nutrients, and ability to grow under a wide range of temperatures, aerobiosis, pH, and water activity as well as to better survive adverse situations, such as
survival of spores at high temperatures. For convenience, bacteria important in foods have been
arbitrarily divided into several groups on the basis of similarities in certain characteristics. This
grouping does not have any taxonomic significance. Some of these groups and their importance
in foods are listed here.
Lactic Acid Bacteria
These bacteria produce relatively large quantities of lactic acid from carbohydrates. Species mainly
from genera Lactococcus, Leuconostoc, Pediococcus, Lactobacillus, and Streptococcus thermophilus are
included in this group.
Acetic Acid Bacteria
These are bacteria that produce acetic acid, such as Acetobacter aceti.
Propionic Acid Bacteria
These bacteria produce propionic acid and are used in dairy fermentation. Species such as
Propionibacterium freudenreichii are included in this group.
Butyric Acid Bacteria
These bacteria produce butyric acid in relatively large amounts. Some Clostridium spp., such as
Clostridium butyricum, are included in this group.
Propionibacterium. Pleomorphic rods (0.5 × 2 μm); can be coccoid, bifid, or branched; present
singly or in short chains; V and Y configuration and in clumps with Chinese-character-like
arrangement; nonmotile; anaerobes; mesophiles. Dairy propionibacteria are used in food
fermentation (Propionibacterium freudenreichii in Swiss cheese). Produce proline and propionic acid. Found in raw milk, Swiss cheese, and silage.
Some New Genera
On the basis of nucleic acid homology studies, several new genera have been created from the existing
genera. Some that are important in food microbiology are listed here. Most of their characteristics are
similar to those of the species in the respective old genera. Examples include Tetragenococcus (from
Pediococcus), Vagococcus (from N-group Streptococcus), Weissella and Oenococcus (both from Leuconostoc),
Kocuria (from Micrococcus), Shewanella (from Pseudomonas), and Alicyclobacillus (from Bacillus).
important Bacterial Groups in Foods
Among the microorganisms found in foods, bacteria constitute major important groups. This is
not only because many different species can be present in foods, but also because of their rapid
growth rate, ability to utilize food nutrients, and ability to grow under a wide range of temperatures, aerobiosis, pH, and water activity as well as to better survive adverse situations, such as
survival of spores at high temperatures. For convenience, bacteria important in foods have been
arbitrarily divided into several groups on the basis of similarities in certain characteristics. This
grouping does not have any taxonomic significance. Some of these groups and their importance
in foods are listed here.
Lactic Acid Bacteria
These bacteria produce relatively large quantities of lactic acid from carbohydrates. Species mainly
from genera Lactococcus, Leuconostoc, Pediococcus, Lactobacillus, and Streptococcus thermophilus are
included in this group.
Acetic Acid Bacteria
These are bacteria that produce acetic acid, such as Acetobacter aceti.
Propionic Acid Bacteria
These bacteria produce propionic acid and are used in dairy fermentation. Species such as
Propionibacterium freudenreichii are included in this group.
Butyric Acid Bacteria
These bacteria produce butyric acid in relatively large amounts. Some Clostridium spp., such as
Clostridium butyricum, are included in this group.