Microorganisms Used in Food Fermentation ◾ 125
infants within 2–3 days after birth and are usually present in high numbers in breast-fed babies.
They are usually found in the large intestine.
Many species of this genus have been isolated from the feces of humans and animals. Some
of these include Bifidobacterium bifidum, Bif. animalis, Bif. longum, Bif. breve, Bif. infantis, Bif.
angulatum, and Bif. adolescentis. 7 The genome sequence of many of the species is now completed.
Many also produce bacteriocins and may play an important role in controlling pathogens during
intestinal colonization in the gut. All have been isolated in humans; however, some species are
more prevalent in infants than in adults. Some of these species have been added to dairy products
to supply live cells in high numbers to restore and maintain intestinal health in humans.
Propionibacterium
This genus includes species in the classical or dairy propionibacterium group and the cutaneous or
acne propionibacterium group. Here, only the dairy group is discussed.
The cells are Gram-positive, pleomorphic thick rods 1–1.5 μm in length and occur in single
cells, pairs, or short chains with different configurations. They are nonmotile, nonsporulating,
anaerobic (can also tolerate air), and catalase positive, and they ferment glucose to produce large
amounts of propionic acid and acetic acid. They also, depending on the species, ferment lactose,
sucrose, fructose, galactose, and some pentoses. They grow optimally at 30°C–37°C. Some species
form pigments. They have been isolated from raw milk, some types of cheeses, dairy products,
and silage.
At present, four species of dairy propionibacterium are included in the genus: Propionibacterium
freudenreichii, Pro. jensenii, Pro. thoenii, and Pro. acidipropionici. All four are associated with natural fermentation of Swiss-type cheeses, but Pro. freudenreichii has been used as a starter culture in
controlled fermentation.
Brevibacterium
The genus contains a mixture of coryniform bacterial species, some of which have important
applications in cheese production and other industrial fermentations. Brevibacterium linens is used
in cheese ripening as it has extracellular proteases. The cells are nonmotile, Gram-positive, and
capable of growing in high salt and wide pH ranges.
Acetobacter
A species in this genus, Acetobacter aceti, is used to produce acetic acid from alcohol. The cells are
Gram-negative, aerobic, rods (0.5–1.5 μm); occurring as single cells, pairs, or chains; and can be
motile or nonmotile. They are obligate aerobes, catalase positive, and oxidize ethanol to acetic acid
and lactic acid to CO 2 and H 2 O. They grow well from 25°C to 30°C. They are found naturally in
fruits, sake, palm wine, cider, beer, sugarcane juice, tea fungus, and soil. Some species synthesize
large amounts of cellulose.
Yeasts and Molds
Many yeasts and molds are important in food, but most are involved with the spoilage of food and
mycotoxin production (by molds). Several are, however, used in food bioprocessing. At present,
infants within 2–3 days after birth and are usually present in high numbers in breast-fed babies.
They are usually found in the large intestine.
Many species of this genus have been isolated from the feces of humans and animals. Some
of these include Bifidobacterium bifidum, Bif. animalis, Bif. longum, Bif. breve, Bif. infantis, Bif.
angulatum, and Bif. adolescentis. 7 The genome sequence of many of the species is now completed.
Many also produce bacteriocins and may play an important role in controlling pathogens during
intestinal colonization in the gut. All have been isolated in humans; however, some species are
more prevalent in infants than in adults. Some of these species have been added to dairy products
to supply live cells in high numbers to restore and maintain intestinal health in humans.
Propionibacterium
This genus includes species in the classical or dairy propionibacterium group and the cutaneous or
acne propionibacterium group. Here, only the dairy group is discussed.
The cells are Gram-positive, pleomorphic thick rods 1–1.5 μm in length and occur in single
cells, pairs, or short chains with different configurations. They are nonmotile, nonsporulating,
anaerobic (can also tolerate air), and catalase positive, and they ferment glucose to produce large
amounts of propionic acid and acetic acid. They also, depending on the species, ferment lactose,
sucrose, fructose, galactose, and some pentoses. They grow optimally at 30°C–37°C. Some species
form pigments. They have been isolated from raw milk, some types of cheeses, dairy products,
and silage.
At present, four species of dairy propionibacterium are included in the genus: Propionibacterium
freudenreichii, Pro. jensenii, Pro. thoenii, and Pro. acidipropionici. All four are associated with natural fermentation of Swiss-type cheeses, but Pro. freudenreichii has been used as a starter culture in
controlled fermentation.
Brevibacterium
The genus contains a mixture of coryniform bacterial species, some of which have important
applications in cheese production and other industrial fermentations. Brevibacterium linens is used
in cheese ripening as it has extracellular proteases. The cells are nonmotile, Gram-positive, and
capable of growing in high salt and wide pH ranges.
Acetobacter
A species in this genus, Acetobacter aceti, is used to produce acetic acid from alcohol. The cells are
Gram-negative, aerobic, rods (0.5–1.5 μm); occurring as single cells, pairs, or chains; and can be
motile or nonmotile. They are obligate aerobes, catalase positive, and oxidize ethanol to acetic acid
and lactic acid to CO 2 and H 2 O. They grow well from 25°C to 30°C. They are found naturally in
fruits, sake, palm wine, cider, beer, sugarcane juice, tea fungus, and soil. Some species synthesize
large amounts of cellulose.
Yeasts and Molds
Many yeasts and molds are important in food, but most are involved with the spoilage of food and
mycotoxin production (by molds). Several are, however, used in food bioprocessing. At present,