Lactic Acid Bacteria

These are gram-positive, non-spore-forming bacteria producing lactic acid as the major or sole product of fermentation. As a group they are important in food spoilage because they cause souring and discoloration. However, they are also very important in pickling, cheese making, fermented dairy products, and silage technologies. The major genera of lactic acid bacteria include Streptococcus, Lac-tococcus, Enterococcus, Pediococcus, Leuconostoc, and Lactobacillus.

Streptococcus species such as S. lactis, S. cremoris, S. thermophilus, and S. diacetilactis are important starter cultures in the dairy industry. Some Streptococcus are pathogenic, such as S. pyogenes and S. faecalis. The dairy Streptococcus cultures are named Lactococcus and fecal Streptococcus cultures are named Enterococcus.

Pediococcus produces large quantities of lactic acid and is very important as a starter culture in the curing of meat.

Leuconostoc produces gas as well as slime in the presence of sugar. Although they are important spoilage organisms, they are also important producers of flavor compounds in dairy products.

Lactobacillus is a heterogeneous group of organisms consisting of slender, gram-positive rods. One group is homofermentative (producing large quantities of lactic acid) and another group is heterofermentative (producing acid and gas). Lactobacillus species are important in dairy, meat, and silage fermentation but are undesirable as spoilage organisms because of the production of large quantities of lactic acid in a variety of food products during storage.

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