EPS FROM L ACTIC A CID B ACTERIA

5.2.2 EPS FROM L ACTIC A CID B ACTERIA

Lactic acid bacteria (LAB) are some of the most thoroughly studied microorganisms and are historically recognized as safe (GRAS) for use in food. Apart from their key role in the production of fermented dairy, meat, and other food products, and their contribution to the sensorial attributes of food, they have recently received increasing attention due to the potential therapeutic properties of some extracellular

polysaccharides (EPSs) that several LAB produce. 75 These biopolymers are usually heteropolysaccharides in the form of slime or a capsule surrounding the cell mem- brane. 75 The main producers of such bioactive compounds identified so far are strains of Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus), 76 Lactobacillus helveti- cus , 77 Lactobacillus casei, 78 Lactococcus lactis ssp. cremoris (L. cremoris), 79 Bifi- dobacterium adolescentis , 80 and Bifidobacterium longum. 81 L. bulgaricus strains excrete different polysaccharides with variable chemical composition, not all of which exhibit immunopotentiating properties. Two EPS fractions, a neutral polysaccharide (NPS) and an acidic polysaccharide (APS), have

been isolated from culture supernatants of L. bulgaricus OLL 1073R-1, 76 while another strain, NCFB 2483, also synthesizes a NPS. These EPSs contain glucose and galactose in the molar ratio (1.0):(1.3 to 1.6), whereas the acidic fraction contains an additional 0.1% of phosporous, which differentiates the APS from the NPS. 82

Indeed, this phosphopolysaccharide with an estimated MW of 1.2 × 10 6 exhibited immunostimulating activity, unlike the NPS. Additionally, another neutral EPS from the L. bulgaricus strain NCFB 2483 provoked no immune responses. 76 The phosphate group in the EPSs of strain OLL 1073R-1 was reported to be a key component, acting as trigger of macrophage functions. 76,82

Lactococcus cremoris SBT 0495 also produces another functional phospho- polysaccharide with both interesting rheological and bioactive properties, viilian, which has been isolated from a Finnish, fermented milk product (viili). 74 Viilian is composed of glucose, galactose, rhamnose, and phosphate with a molar ratio of 2:2:1:1. Its structure is shown in Figure 5.3. 83 Viilian is separated from an initial

Functional Food Carbohydrates

α-L-Rhap

2 ϭ4)-β-D-Glcp-(1ϭ4)-β-D-Galp-(1ϭ4)-β-D-Glcp-(1ϭ

α-D-Galp-1-PO -

FIGURE 5.3 Structure of the repeating unit of viilian produced by Lactococcus lactis ssp. cremoris SBT 0495. (From Oba, T. et al., Arch. Microbiol., 171, 343, 1999. With permission.)

protein–polysaccharide mixture excreted by the microorgranism, after elimination of the protein moiety, the concentration of which varies in analogy with the protein content of the culture medium. 84

In contrast to the above extracellular LAB polysaccharides, Bifidobacterium species contain antitumor polysaccharides in their cell walls. A water-soluble polysaccharide extracted from Bifidobacterim adolescentis strain M101-4 was exam-

ined by Hosono et al. 80 It consisted of major residues of -4-galactopyranose-1, -4- glucopyranose-1, and -6-glucopyranose-1, and minor residues of galactofuranose-1 and -6-galactofuranose-1. The characteristic galactofuranosyl segments were unique among all previously studied soluble biopolymers of Gram-positive bacteria. 80 Another crude polysaccharide isolated from Bifidobacterium longum strains was found to be responsible for the antimutagenic effects of skim milk fermented with

B. longum , although its chemical composition was not fully elucidated. 81 These examples of LAB polysaccharides with therapeutic properties show the potential for introduction of new functional food products in the market. Since the addition of LAB (or their bioproducts), in particular, in food is already prac- ticed for technological reasons, and their acceptance by consumers is ensured, the production of food or nutraceuticals containing LAB polysaccharides as active compounds (such as fermented milk, cheese, and yogurt) is probably a realistic prospect for food scientists and the food market. However, careful selection of the proper strain is necessary, as the desired physiological functions may be specific to a certain strain.