Fundamental Food Microbiology, Third Edition - Fuad Fathir

MICROORGANISMS USED IN FOOD FERMENTATION 129
anaerobes and in glucose broth can reduce the pH to 4.0 and produce L(+)-lactic
acid. They ferment fructose, mannose, and lactose, but generally not galactose and
sucrose. Cells survive 60ºC for 30 min. Their natural habitat is unknown, although
they are found in milk.
C. Leuconostoc
The Gram-positive cells are spherical to lenticular, arranged in pairs or in chains,
nonmotile, nonsporulating, catalase negative, and facultative anaerobes (Figure
10.1). The species grow well between 20 and 30ºC, with a range of 1 to 37ºC.
Glucose is fermented to D(–)-lactic acid, CO 2, ethanol, or acetic acid, with the pH
reduced to 4.5 to 5.0. The species grow in milk but may not curdle. Also, arginine
is not hydrolyzed. Many form dextran while growing on sucrose. Citrate is utilized
to produce diacetyl and CO 2. Some species can survive 60ºC for 30 min. Leuconostoc
species are found in plants, vegetables, silage, milk and some milk products, and
raw and processed meats. 2,4
At present, five species are known: Leuconostoc mesenteroides, Leu. paramesenteroides,
Leu. lactis, Leu. carnosum, and Leu. gelidum. Leu. mesenteroides has
three subspecies: subsp. mesenteroides, ssp. dextranicum, and ssp. cremoris. Leu.
mesenteroides ssp. cremoris and Leu. lactis are used in some dairy and vegetable
fermentations. Many of these species, particularly Leu. carnosum and Leu. gelidum,
have been associated with spoilage of refrigerated vacuum-packaged meat products. 5
Leuconostocs are morphologically heterogenous and may contain genetically
diverse groups of bacteria. Recently, two new genera have been created from it:
Weisella and Oenococcus. Oen. oeni is found in wine and related habitant and is
used for malolactic fermentation in wine.
D. Pediococcus
The cells are spherical and form tetrads, but they can be present in pairs. Single
cells or chains are absent (Figure 10.1). They are Gram-positive, nonmotile, nonsporulating,
facultative anaerobes. They grow well between 25 and 40�C; some
species grow at 50�C. They ferment glucose to L(+)- or DL-lactic acid, some species
reducing the pH to 3.6. Depending on the species, they can ferment sucrose, arabinose,
ribose, and xylose. Lactose is not generally fermented, especially in milk, and
milk is not curdled. 2 Some strains may have weak lactose-hydrolyzing capability,
especially in broth containing lactose as a carbohydrate source.
Depending on the species, they are found in plants, vegetables, silage, beer, milk,
and fermented vegetables, meats, and fish. The genus has seven to eight species, of
which Ped. pentosaceus and Ped. acidilactici are used in vegetables, meat, cereal,
and other types of fermented foods. They have also been implicated in ripening and
flavor production of some cheeses as secondary cultures. These two species are
difficult to differentiate, but compared with Ped. acidilactici, Ped. pentosaceus ferments
maltose, does not grow at 50ºC, and is killed at 70ºC in 5 min. 2 Ped. halophilus,
used in fermentation of high-salt products, is now classified as Tet. halophilus.
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