Microorganisms Used in Food Fermentation ◾ 121
Lactococcus
This genus includes several species, but only one species, Lactococcus lactic, has been widely used
in dairy fermentation. It has three subspecies (ssp.); lactis, cremoris, and hordniae, but only the first
two are used in dairy fermentation. The biovar Lac. lactis ssp. lactis biovar diacetylactis is also used
in dairy fermentation.
The cells are ovoid, approximately 0.5–1.0 μm in diameter, present in pairs or short chains,
nonmotile, nonsporulating, and facultative anaerobic to microaerophilic (Figure 11.1). In general,
they grow well between 20°C and 30°C but do not grow in 6.5% NaCl or at pH 9.6. In a suitable
broth, they can produce approximately 1% l(+)-lactic acid and reduce the pH to approximately
4.5. Subsp. cremoris can be differentiated from subsp. lactis by its inability to grow at 40°C, in 4%
NaCl, ferment ribose, and hydrolyze arginine to produce NH 3 . Biovar diacetylactis, as compared
with others, produces larger amounts of CO 2 and diacetyl from citrate. They are generally capable
of hydrolyzing lactose and casein. They also ferment galactose, sucrose, and maltose. Natural
habitats are green vegetation, silage, the dairy environment, and raw milk.
(a)
(b)
(c)
(d)
(e)
Figure 11.1 Photograph of lactic acid bacteria: (a) Lactococcus lactis, (b) Streptococcus thermophilus, (c) Leuconostoc mesenteroides, (d) Pediococcus acidilactici, and (e) Lactobacillus
acidophilus.
Lactococcus
This genus includes several species, but only one species, Lactococcus lactic, has been widely used
in dairy fermentation. It has three subspecies (ssp.); lactis, cremoris, and hordniae, but only the first
two are used in dairy fermentation. The biovar Lac. lactis ssp. lactis biovar diacetylactis is also used
in dairy fermentation.
The cells are ovoid, approximately 0.5–1.0 μm in diameter, present in pairs or short chains,
nonmotile, nonsporulating, and facultative anaerobic to microaerophilic (Figure 11.1). In general,
they grow well between 20°C and 30°C but do not grow in 6.5% NaCl or at pH 9.6. In a suitable
broth, they can produce approximately 1% l(+)-lactic acid and reduce the pH to approximately
4.5. Subsp. cremoris can be differentiated from subsp. lactis by its inability to grow at 40°C, in 4%
NaCl, ferment ribose, and hydrolyze arginine to produce NH 3 . Biovar diacetylactis, as compared
with others, produces larger amounts of CO 2 and diacetyl from citrate. They are generally capable
of hydrolyzing lactose and casein. They also ferment galactose, sucrose, and maltose. Natural
habitats are green vegetation, silage, the dairy environment, and raw milk.
(a)
(b)
(c)
(d)
(e)
Figure 11.1 Photograph of lactic acid bacteria: (a) Lactococcus lactis, (b) Streptococcus thermophilus, (c) Leuconostoc mesenteroides, (d) Pediococcus acidilactici, and (e) Lactobacillus
acidophilus.