Develop novel polysaccharides.

Worldwide, the food industry is using 70,000 tons annually of polysaccharides as thickening agents, stabilizers and texturizers. Polysaccharides naturally present in foods often contribute significantly to food texture and palatability. Such carbohydrate macromolecules include starch, cellulose, pectin, guar gum, alginate, carageenan and the microbial xanthan.

We know that lactic acid bacteria produce numerous exopolysaccharides (EPS) during fermentation. Microbial EPS produced by the bacteria are interesting. Their viscosity-enhancing effect is due to a combination of structure and molecular mass. Incorporating them into a dough of a sufficient amount can result in an improved texture because they soften the gluten content of the dough. They also extend the shelf life and increase the specific volume of the resultant bakery product.

An example of EPS is the use of LAB dextrans or polymers of alpha(1-6)-linked D-glucose residues as additive. There also is an alternative application of a functional LAB starter culture for the in situ production of specific metabolites and EPS in fermented doughs. The use of EPS-producing sourdough LAB is very promising for improving textural and sensorial bread quality.

EPS help create the texture of fermented foods, such as yogurt. The objective of ongoing European research is to establish fermentation protocols for producing stable functional polysaccharides, in particular from the yogurt starter culture Streptococcus thermophilus.

The focus of the research is on structure and yields of EPS, on how they may be controlled at the genetic and biochemical level, on process engineering and on structure-function relationships. First results show that S. thermophilus strains produce two heteropolysaccharides with the same monomeric composition--galactose and glucose in a 4:1 ratio--but with different molecular masses. Researchers have gained much knowledge on how to optimize EPS production, EPS variability, biosynthesis, structure and genetic relationships.

Further information. Valerie Marshall, University of Huddersfield, School of Applied Sciences, Queensgate, HD1 3DH Huddersfield, U.K.; phone: [phone]; fax: [phone]; email: [e-mail].