Lactic acid bacteria produce a lot of lactic acid from several types of sugars. They are gram-positive rod-type or spherical bacteria which can grow under an anaerobic condition. They show no mobility and negative in a catalatic reaction. They form no spores. They use only sugars as an energy source to yield lactic acid, and convert more than 50% of the consumed sugars. There are the following four groups in the bacterial species to satisfy the above-mentioned conditions: Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus. Lactic acid bacteria can grow with higher growth rates and produce lactic acid with higher productivities. Since they request a lot of nutrients including amino acids and vitamins, the composition of the fermentation broth is not simple. We can classify lactic acid fermentation into two groups, homo-lactic acid fermentation and hetero-lactic acid fermentation. In the homo fermentation two moles of lactic acid and two moles of ATP can be produced from one mole of mono-saccharides with almost 100% of the lactic yield. On the other hand, in the hetero fermentation, lactic acid and other compounds are produced; it is classified into two groups: 1) one yielding lactic acid, ethanol and carbon dioxide. 2) one yielding one mole of lactic acid and

1.5 moles of acetic acid from one mol of mono-saccharides. Lactic acid bacteria possess both D type and L type or either D type or L type of lactate-dehydrogenases. Thus D-lactic acid and (or) L-lactic acid can be produced by the bacteria. Most of lactic acid bacteria has enzymes

which racemize the produced lactic acid, affecting the chiral quality of lactic acid. Lactobacillus

rhamnosus can produce only L-lactic acid with almost 100% of the optical purity, which is used as a raw material for the poly-lactate production.