Characterization of exopolysaccharide produced by a corynebacterium in cheese whey substrate

A Corynebacterium designated #98 was found to produce an orange pigmented exopolysaccharide in high yield when grown at optimum conditions in a cheese whey substrate. Sweet whey was reconstituted and deproteinized by lowering the pH to 5.0 and autoclaving. The whey solution was enriched with MgS0₄, FeS0₄, lactose, its pH was adjusted to 7.0 with 1 N NaOH, and the solution was autoclaved. The Corynebacterium #98 was cultivated in Tryptic Soy Broth (TSB) for 24 hours and then inoculated into 1.5% whey substrate. This was incubated at 30°C in a shaker bath for 7 days. The viscous culture medium was inoculated later at a rate of 15% into a 2-liter fermentor with agitation of 200 rpm, air flow of 1090 ml/min., and temperature of 30°C. After 15 days, the viscous material was precipitated by a mixture of acetone, phosphate buffer, and saturated KCl. The gum was freeze-dried and stored. The rheology of the gum indicated that it is a shear thickening (dilatant) polysaccharide. The viscosity increased with increasing gum concentration and pH, and decreased with increasing salt (NaCl) con-centration. The emulsifying capacity was 17.02 ml of vegetable oil/g of gum. Analysis indicated that the freeze-dried gum consisted of 5.93% moisture, 1.11% ether extract, 4.06% protein, 29.67% ash, and 59.23% nitrogen free extract. Mineral determination showed high levels of potassium and sodium, some chloride and phosphate, and low levels of calcium, magnesium, iron, and silica. The monosaccharide constituents of the gum as determined by gas chromatography were rhamnose, xylose, mannose, glucose, galactose, glucuronic acid, and mannuronic acid in a ratio of 2:1:6:6:7:16:11.