PRODUCTION

Over the past 20 years, bacteria have become an increasingly important source of polysaccharides. Dextran, a blood plasma extender and a key constituent of certain types of chromatographic materials, and xanthan gum, the most extensively tested and one of the most intensively researched food polysaccharides, are good examples of bacterial polysaccharides. Kelco Division of Merck & Co.Inc. has pioneered the development of bacterial polysaccharides and has now isolated in excess of 900 gum-forming bacteria. Although all of the gums produced by these bacteria are of scientific interest, most are not of commercial value because they do not offer significant advantages over existing alternatives. However, there are a few notable exceptions, namely rhamsan gum (S-194), a more efficient suspending agent than xanthan gum; Biozan welan gum ( S-130), a thickener for oil-field applications with superior thermal stability to xanthan gum and gellan gum ( S-60), a novel gelling polysaccharide.

Gellan gum offers a potential solution to many of the problems that exist with current gelling agents. Being a fermentation product, it can be produced on demand and with consistent quality. Availability and variability are, thus, not concerns. It is functional at very low use levels and is therefore, very efficient in many applications. Gellan gum can provide a range of gel textures as opposed to a single characteristic texture. Consequently, it can be used to mimic the texture of existing gelling agents or to create new textures. In today’s food industry, a tool to create new textures and hence permit the creation of new , differentiated food products would be highly desirable. Gellan gum is not a difficult product to use and although it is anticipated that eventually various form for a particular application will be determined by textural rather than by complex functional considerations. It should be stressed that gellan gum is in its early development stage, and much still has to be learned about its basic chemistry, properties, applications and , indeed, its ultimate utility in the market place. In this respect, it is encouraging that, for the first time in the history of hydrocolloids, commercial development is proceeding in parallel with the generation of fundamental scientific data on the product. Gellan gum is produced by the bacterium Pseudomonas elodea. The gum is formed by inoculating a carefully formulated fermentation medium with this organism. The medium consists of a carbon source such as glucose, a nitrogen source and a number of inorganic salts. The fermentation is allowed to proceed under sterile conditions with strict control of aeration, agitation, temperature and pH. When fermentation is complete, the viscous broth is pasteurized to kill the viable cells and then subsequently processed to recover the polysaccharide in either the fully acylated native form or the deacylated form, as show in Fig.2. Gelrite-gellan gum for microbiological media and related applications and Kelcogel food grade gellan gum ---are low acyl products. Gels from the native material can loosely be described as cohesive and elastic, while those from the deacylated materials are strong and brittle. Materials of intermediate acyl content, which can be obtained by careful control of the deacylation step, provide gel textures intermediate between those of the native and fully deacylated products.