**1. Introduction**

Lactic acid bacteria (**LAB**) are used in many fermented foods, particularly fermented dairy products such as cheese, buttermilk, and fermented milks. LAB produce lactic acid, carbon dioxide, and diacetyl/acetoin that contribute to the flavor, texture, and shelf life of fermented foods. Some LAB produce exopolysaccharide (EPS), and generally, EPS play a major role as natural texturizer in the industrial production of yoghurt, cheese, and milkbased desserts. Recently, EPS produced by LAB have received increasing attention, mainly because of their health benefits. In particular, immune stimulation, antimutagenicity, and the antitumor activity of fermented dairy products prepared with EPS-producing LAB or EPS themselves have been investigated [1-4].

EPS are polysaccharides secreted from the cell, or produced on the outer cell by extracellular enzymes. EPS from LAB are divided into two classes, homo- and hetero-EPS. Homo-EPS are composed of one type of monosaccharide, whereas hetero-EPS consist of regular repeating units of 3-8 different carbohydrate moieties synthesized from intracellular sugar nucleotide precursors [5]. The biosynthesis of homo-EPS and hetero-EPS are different. Homo-EPS are made from sucrose using glucansucrase or levansucrase [6-7], and the synthesis of hetero-EPS involves four major steps, sugar transportation, sugar nucleotide synthesis, repeating unit synthesis, and polymerization of the repeating units [8]. The major physiological function of EPS is believed to be biological defenses against various stresses such as phage attack, toxic metal ions, and desiccation [9], and it is very unlikely that bacteria use EPS as an energy source. However, some potentially probiotic LAB strains have been reported to degrade EPS produced by the other LAB strains [10-11].

The term "probiotic" was first proposed by Fuller [12], and its definition was further refined to "Live microorganisms which when consumed in adequate amounts as part of food confer a health benefit on the host" [13]. Probiotic LAB thus represent a class of live food

© 2013 Harutoshi, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ingredients that exert a beneficial effect on the health of the host. Beneficial microorganisms in the intestine are enhanced by "prebiotics," which are defined as "nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and activity of one or a limited number of bacterial species already resident in the colon, and thus improving host health" [14].

Exopolysaccharides of Lactic Acid Bacteria for Food and Colon Health Applications 517

Organism

*Lb. curvatus* 

*Str. mutans* 

*Leuc. mesenteroides* 

*Str. mutans* 

*Leuc. mesenteroides, Lb. reuteri* 

*Leuc. mesenteroides* subsp*. mesenteroides, Leuc. mesenteroides* subsp*.* 

*dextranicum, Leuc. amelibiosum,* 

Homo-EPS Main linkage

Glucans Dextran

Mutan

Alternan

Fructans Levan

Inulin

(branching linkage)

O HO O OH

O HO O OH

O HO O OH

CH2OH

O

CH2OH

CH2

O HO O OH OH

O HO O OH

O HO O OH OH

n

n

O

CH2OH

CH2

O OH H2C HO OH

O O

O O

<sup>O</sup> <sup>O</sup> CH2 HO OH

CH2OH

CH2OH

CH2OH

CH2 HO OH

n

CH2 HO OH

n

CH2OH

n

O HO O OH OH

O HO O OH

O HO O OH

> O O H2C HO OH

CH2OH

CH2OH

CH2

CH2

CH2

α-1,6 (α-1,3)

CH2OH

O HO O OH OH

O HO O OH

CH2OH

O HO O OH OH

O HO O OH OH

CH O <sup>2</sup>

CH O <sup>2</sup>

α-1,3 (α-1,6)

O HO O OH OH

CH2

CH2OH

O

α-1,3 and α-1,6

O OH HO OH

OH O <sup>O</sup> OH H2C HO OH CH2

β-2,6 (β-2,1)

β-2,1 (β-2,6)

**Table 1.** Homo EPS produced by LAB

Most of the current prebiotics are low molecular weight except for inulin. As long carbohydrate chains are metabolized more slowly than the short ones, and polysaccharides thus exert prebiotic effects in more distal colonic regions compared to oligosaccharides, which are more rapidly digested in the proximal colon [15]. Therefore, EPS produced by LAB can be used as prebiotics. This chapter reviews the physicochemical properties, genetics, and bioactivities of the EPS produced by LAB.
