Microscopic and chemical studies of a gelling polysaccharide from Lactobacillus hilgardii

The bacterium Lactobacillus hilgardii (previously named L. brevis), isolated from sugary kefir grains, has been found to produce a gelling extracellular polysaccharide. Methylation analysis and ¹H- and ¹³C-NMR analysis revealed a dextran-like structure for the polysaccharide. A high proportion of -(1,6)-Glc and small proportions of -(1,3,6)-Glc, -(1,4,6)-Glc and terminal -Glc were detected. The L. hilgardii polysaccharide differed from normal dextrans in containing a small proportion of -(1,3)-Glc. The structure of the polysaccharide was found to be independent of harvesting time and unaffected by changes in the growth medium. The development of the gel structure has been followed by transmission electron microscopy.