Microorganisms Used in Food Fermentation ◾ 123
Lactobacillus
The genus Lactobacillus includes a heterogenous group of Gram-positive, rod-shaped, usually
nonmotile, nonsporulating, facultative anaerobic species that vary widely morphologically and in
growth and metabolic characteristics (Figure 11.1). Cells vary from very short (almost coccoid) to
very long rods, slender or moderately thick, often bent, and can be present as single cells or in short
to long chains. While growing on glucose, depending on the species, they produce either only
lactic acid [l(+), d(–), or DL] or a mixture of lactic acid, ethanol, acetic acid, and CO 2 . Some also
produce diacetyl. Many species utilize lactose, sucrose, fructose, or galactose, and some species
can ferment pentoses. Growth temperature can vary from 1°C to 50°C, but most that are used as
starter cultures in controlled fermentation of foods grow well from 25°C to 40°C. Several species
involved in natural fermentation of some foods at low temperatures can grow well from 10°C to
25°C. While growing in a metabolizable carbohydrate, depending on the species, the pH can be
reduced to between 3.5 and 5.0.
They are distributed widely and can be found in plants; vegetables; grains; seeds; raw and
processed milk and milk products; raw, processed, and fermented meat products; and fermented
vegetables; some are found in the digestive tract of humans, animals, and birds. Many have been
associated with spoilage of foods.
Among the large number of species, some have been used in controlled fermentation (dairy,
meat, vegetables, and cereal), some are known to be associated with natural fermentation of foods,
a few are consumed live for their beneficial effect on intestinal health, and some others have an
undesirable effect on foods. On the basis of their metabolic patterns of hexoses and pentoses
(discussed in Chapter 12), the species have been divided into three groups (Table 11.1). Those
in Group I ferment hexoses (and disaccharides, such as lactose and sucrose) to produce mainly
lactic acids and do not ferment pentoses (such as ribose, xylose, or arabinose). Those in Group II,
depending on the carbohydrates and the amounts available, either produce mainly lactic acid, or a
mixture of lactic, acetic, and formic acids; ethanol; and CO 2 . Group III species ferment carbohydrates to a mixture of lactate, acetate, ethanol, and CO 2 .
The three Lactobacillus delbrueckii subspecies are used in the fermentation of dairy products,
such as some cheeses and yogurt. They grow well at 45°C and ferment lactose to produce large
amounts of d(–) lactic acid. β-Galactosidase in these subspecies is constitutive. Lactobacillus acidophilus and Lab. reuteri are considered to be beneficial intestinal microbes (probiotic) and are
present in the small intestine. Lab. acidophilus is used to produce fermented dairy products and
also either added to pasteurized milk or made into tablets and capsules for consumption as probiotics. It metabolizes lactose and produces large amounts of d(–)-lactic acid. However, in Lab.
acidophilus, β-galactosidase is generally inducible. Lab. helveticus is used to make some cheeses and
ferment lactose to lactic acid (DL). Lab. casei ssp. casei is used in some fermented dairy products.
It ferments lactose and produces l(+)-lactic acid. Some strains are also used as probiotic bacteria.
Strains of Lab. casei ssp. rhamnosus (also called Lab. rhamnosus) are now used as a probiotic bacterium. Some strains of Lab. johnsonii are also used in probiotics. Lab. plantarum is used in vegetable
and meat fermentation. It produces dl-lactic acid. Lab. curvatus and Lab. sake can grow at low
temperatures (2°C–4°C) and ferment vegetable and meat products. Lab. sake is used to ferment
sake wine. Lab. kefir is important in the fermentation of kefir, an ethnic fermented sour milk.
Lab. sanfrancisco is associated with other microorganisms in the fermentation of San Francisco
sourdough bread. Lab. viridescens, Lab. curvatus, and Lab sake are associated with spoilage of
refrigerated meat products.
Lactobacillus
The genus Lactobacillus includes a heterogenous group of Gram-positive, rod-shaped, usually
nonmotile, nonsporulating, facultative anaerobic species that vary widely morphologically and in
growth and metabolic characteristics (Figure 11.1). Cells vary from very short (almost coccoid) to
very long rods, slender or moderately thick, often bent, and can be present as single cells or in short
to long chains. While growing on glucose, depending on the species, they produce either only
lactic acid [l(+), d(–), or DL] or a mixture of lactic acid, ethanol, acetic acid, and CO 2 . Some also
produce diacetyl. Many species utilize lactose, sucrose, fructose, or galactose, and some species
can ferment pentoses. Growth temperature can vary from 1°C to 50°C, but most that are used as
starter cultures in controlled fermentation of foods grow well from 25°C to 40°C. Several species
involved in natural fermentation of some foods at low temperatures can grow well from 10°C to
25°C. While growing in a metabolizable carbohydrate, depending on the species, the pH can be
reduced to between 3.5 and 5.0.
They are distributed widely and can be found in plants; vegetables; grains; seeds; raw and
processed milk and milk products; raw, processed, and fermented meat products; and fermented
vegetables; some are found in the digestive tract of humans, animals, and birds. Many have been
associated with spoilage of foods.
Among the large number of species, some have been used in controlled fermentation (dairy,
meat, vegetables, and cereal), some are known to be associated with natural fermentation of foods,
a few are consumed live for their beneficial effect on intestinal health, and some others have an
undesirable effect on foods. On the basis of their metabolic patterns of hexoses and pentoses
(discussed in Chapter 12), the species have been divided into three groups (Table 11.1). Those
in Group I ferment hexoses (and disaccharides, such as lactose and sucrose) to produce mainly
lactic acids and do not ferment pentoses (such as ribose, xylose, or arabinose). Those in Group II,
depending on the carbohydrates and the amounts available, either produce mainly lactic acid, or a
mixture of lactic, acetic, and formic acids; ethanol; and CO 2 . Group III species ferment carbohydrates to a mixture of lactate, acetate, ethanol, and CO 2 .
The three Lactobacillus delbrueckii subspecies are used in the fermentation of dairy products,
such as some cheeses and yogurt. They grow well at 45°C and ferment lactose to produce large
amounts of d(–) lactic acid. β-Galactosidase in these subspecies is constitutive. Lactobacillus acidophilus and Lab. reuteri are considered to be beneficial intestinal microbes (probiotic) and are
present in the small intestine. Lab. acidophilus is used to produce fermented dairy products and
also either added to pasteurized milk or made into tablets and capsules for consumption as probiotics. It metabolizes lactose and produces large amounts of d(–)-lactic acid. However, in Lab.
acidophilus, β-galactosidase is generally inducible. Lab. helveticus is used to make some cheeses and
ferment lactose to lactic acid (DL). Lab. casei ssp. casei is used in some fermented dairy products.
It ferments lactose and produces l(+)-lactic acid. Some strains are also used as probiotic bacteria.
Strains of Lab. casei ssp. rhamnosus (also called Lab. rhamnosus) are now used as a probiotic bacterium. Some strains of Lab. johnsonii are also used in probiotics. Lab. plantarum is used in vegetable
and meat fermentation. It produces dl-lactic acid. Lab. curvatus and Lab. sake can grow at low
temperatures (2°C–4°C) and ferment vegetable and meat products. Lab. sake is used to ferment
sake wine. Lab. kefir is important in the fermentation of kefir, an ethnic fermented sour milk.
Lab. sanfrancisco is associated with other microorganisms in the fermentation of San Francisco
sourdough bread. Lab. viridescens, Lab. curvatus, and Lab sake are associated with spoilage of
refrigerated meat products.