Heteropolysaccharides from lactic acid bacteria

Microbial exopolysaccharides are biothickeners that can be added to a wide variety of food products, where they serve as viscosifying, stabilizing, em ulsifying or gelling agents. Numerous exopolysaccharides with different com position, size and structure are synthesized by lactic acid bacteria. The h eteropolysaccharides from both mesophilic and thermophilic lactic acid bact eria have received renewed interest recently. Structural analysis combined with rheological studies revealed that there is considerable variation amon g the different exopolysaccharides; some of them exhibit remarkable thicken ing and shear-thinning properties and display high intrinsic viscosities. H ence, several slime-producing lactic acid bacterium strains and their biopo lymers have interesting functional and technological properties, which may be exploited towards different products, in particular, natural fermented m ilks. However, information on the biosynthesis, molecular organization and fermentation conditions is rather scarce, and the kinetics of exopolysaccha ride formation are poorly described. Moreover, the production of exopolysac charides is low and often unstable, and their downstream processing is diff icult. This review particularly deals with microbiological, biochemical and technological aspects of heteropolysaccharides from, and their production by, lactic acid bacteria. The chemical composition and structure, the biosy nthesis, genetics and molecular organization, the nutritional and physiolog ical aspects, the process technology, and both food additive and in situ ap plications (in particular in yogurt) of heterotype exopolysaccharides from lactic acid bacteria are described. Where appropriate, suggestions are made for strain improvement, enhanced productivities and advanced modification and production processes (involving enzyme and/or fermentation technology) that may contribute to the economic soundness of applications with this pro mising group of biomolecules. (C) 1999 Federation of European Microbiologic al Societies. Published by Elsevier Science B.V. All rights reserved.