Phisical and chemical properties of exopolysaccharide of the lactic streptococcus

Abstract

We know that exopolysaccharides of microbial origin are of great practical importance, and have their industrial value because of the biological and physico - chemical characteristics of the producer. We had a goal to study the most important properties of an exopolysaccharide isolated from a bacterial culture of Streptococcus thermophilus. First we got exopolysaccharide. After that we had cultured the bacteria on A. Welman at 38 °C for 48 hours. To do this, 3000 g of culture liquid had been centrifuged for 30 minutes. Next, we removed the biomass sludge, and we evaporated the centrifuge on a rotary evaporator. After that, we precipitated the exopolysaccharide with a double volume of 96% ethyl alcohol. We got a concentrate which we then dissolved in a small amount of distilled water and had centrifuged for 30 minutes. Afterwards my colleges and I precipitated it again. Our further purification of the exopolysaccharide we had to perform using some gel filtration on a column with a Sephadex G-50. It had to be dried on a freeze dryer. Thus, we obtained an exopolysaccharide in the form of a light brown powder, it was odorless, without any foreign impurities and any producer cells. Our further work included following steps: we had to know the molecular weight of the exopolysaccharide. It was possible to make with gel chromatography on a Toyopearl – HW –50F column. We determined the chemical nature of the exopolysaccharide through ion exchange chromatography using a SPS Bio DEA medium with 70 microns. We determined the monosaccharide composition with the help of a thin-layer chromatography on DC-Alufolien Cellulose plates, and the relative viscosity by viscometer. As a result of our research, the exopolysaccharide S. thermophilus were presented by a single neutral fraction, with molecular weight of 20,000 Da, with a small relative viscosity.