Microbial polysaccharides are used for a broad variety of industrial applications including food production, chemical production (e.g., detergents, cosmetics, paints, pesticides, fertilizers, flocculants, film formers, lubricants and explosives), pharmaceutical production and waste treatment. In food production, microbial polysaccharides are commonly used as thickening, gelling and homogenizing agents. When added to a liquid, microbial biopolymers contribute to viscosity, emulsion stabilization, surface tension and adhesiveness. Thickening applications are particularly important in the production of solid and semi-solid food products including dairy and non-dairy foods such as yogurt, buttermilk, salad dressings, cheese, and ice-cream. Thickening of liquid foods is desirable because of consumer preference for such thickened foods, which have a characteristic texture and “mouth feel.” Thickening of liquid drinks is also desirable for use with elderly people who frequently have problems swallowing low-viscosity liquids (e.g., milk and fruit juices) due to an impaired swallowing reflex. The addition of thickener to such drinks facilitates swallowing and reduces aspiration of liquid into the trachea.
Currently the only microbial polysaccharides used to any appreciable extent in industry are dextran, produced by Leuconostoc mesenteroides, xanthan gum, produced by Xanthomonas campestris, and gellan gum, produced by Aureomonas elodea ATCC31461 (Crescenzi, Biotech. Prog. 11:251-259, 1995). Xanthan gum was approved by the U.S. Food and Drug Administration (FDA) for use in foods in 1969. Today it is used in many foods such as bakery fillings, canned foods, frozen foods, pourable dressings, sauces, gravies, processed cheeses, and juice drinks. Xanthan gum is also used in oil recovery, pharmaceuticals, beauty products, and coating agents.
Unfortunately, Xanthomonas campestris is a less than ideal source of polysaccharides for use in food production, since it is known to be pathogenic, and the biopolymer it produces has long been suspected of being pyrogenic (fever-inducing). Although xanthan gum is classified as “Generally Regarded as Safe” (GRAS) by the Food and Drug Administration (FDA), Xanthomonas campestris is not.
Lactic acid bacteria (LAB) are classified GRAS, and have been used for centuries in fermented dairy products such as yogurt, cheese, and sour-cream. A characteristic of some LAB in food production processes is their production of exopolysaccharides (EPS). EPS provide improved viscosity and mouth-feel while also preventing syneresis (separation) in fermented food products. Despite their ability to produce EPS, LAB are not generally used as sources of thickening agents (either within a milk-based culture or as a source of exogenous EPS) because the EPS-positive phenotype is readily lost (Dierkesen et al., J. Dairy Sci. 80(8):1528-1536, 1997). The LAB strain described in this disclosure stably produces EPS when cultivated on appropriate media.