Biosynthesis, Purification and Biotechnological Use of Exopolysaccharides Produced by Lactic Acid Bacteria

Food Additive 84 properties of dairy products.When they are added to food, polysaccharides show functions as thickeners, stabilizers, emulsifiers, gelling agents, and water binding agents (Kimmel et al., 1998).They also contribute to preservation, and enhance the organoleptic characteristics of milk and dairy products such as flavour and aroma (Macedo et al., 2002).More recently, these bio-molecules have been regarded as health promoters due to their role as prebiotics and/or the immunomodulatory properties linked to their structure.As a result, a number of studies are in progress in order to characterize the unmapped diversity of the EPS produced by LAB, since they are considered food-grade organisms.In this chapter, we shall review the current knowledge pertaining to the EPS synthesized by LAB, from biogenesis to application, detailing their nature and structure.Moreover, the methods most frequently used for the production and purification of these biopolymers will be presented. Composition, structure and classification of EPSThe EPS synthesized by LAB vary greatly in their chemical composition, structure and molecular weight.According to their chemical composition, EPS are classified into heteropolysaccharides (HePS) and homopolysaccharides (HoPS).HePS are constructed of a backbone of repeated subunits that are linear or branched, with variable molecular masses (up to 10 6 Da).Each one of these subunits can contain between three and eight different monosaccharides and frequently has a range of different linkage patterns.The monosaccharides are present as the αor β-anomer in the pyranose or furanose form and D-glucose, D-galactose and L-rhamnose are the most frequently encountered.In few cases, N-acetylglucosamine, manose, fucose, glucuronic acid and noncarbohydrate substituents (phosphate, acetyl and glycerol) are also present (de Vuyst & Degeest, 1999;de Vuyst et al., 2001).Different strains of LAB isolated from dairy products, cereals and alcoholic beverages synthesize HePS.These belong to the genera Lactococcus (L.lactis subsp.