Biosynthesis, purification and biotechnological use of exopolysaccharides produced by lactic acid bacteria

MARÍA LAURA WERNING,; SARA NOTARIAGO; NÁCHER-VÁZQUEZ, MONTSERRAT; PILAR FERNÁNDEZ DE PALENCIA; ROSA AZNAR; PALOMA LÓPEZ

Food Additive

Yehia El- Samragy. IN-Tech open Science

Año: 2012; p. 83 - 114

Polysaccharides have been used traditionally by the food industry for their viscosifying, emulsifying and biothickening properties and more recently for manufacture of functional food due to their prebiotic and immunomodulating properties. Bacteria can synthesize cytoplasmic storage polysaccharides (e.g. glycogen), cell wall structural polysaccharides such as peptidoglycan, and lipoteichoic acids of gram-positive bacteria, and the lipopolysaccharides anchored in the outer membrane of gram-negative bacteria. In addition, some bacteria can secrete polysaccharide layers on their surface, which together with a few glycoproteins, constitute the glycocalyx. These exocellular polymers comprise the capsular polysaccharides, which form a cohesive layer or capsule covalently linked to the cell surface, and the exopolysaccharides (EPS), which form a slime layer loosely attached to the cell surface or secreted into the environment (Brock, 2008). The physiological role of these molecules are not yet clearly understood, although it is generally recognized that exocellular polysaccharides are not normally used as energy and carbon sources by the producing microorganism. They can serve for a variety of functions including cell recognition and interaction, adherence to surfaces and biofilm formation. The majority of the polysaccharides used as additives by the food industry such as pectin, cellulose and alginate are obtained from plants and algae. However, other biopolymers like xanthan and gellan, also used as bio-thickeners, are synthesized by gram-negative bacteria. Furthermore, lactic acid bacteria (LAB) producing EPS are used mainly in the dairy industry for improvement of the rheological properties of fermented products as well as for the manufacture of functional food. The taste/texture benefits of the EPS produced by LAB in fermented foods are well established, because these organisms produce polymers that improve the rheological 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.