Abstract:

Generally, the purity of crude polysaccharide extracted from Bletilla striata roots applied in Chinese traditional medicine is no higher than 80%, which seriously restricts its further utilization as an additive or a medicine material. In order to purify the crude polysaccharide extracted from Bletilla striata roots using 80% ethanol, this study employed the enzymatic hydrolysis technology to remove protein impurities from the crude polysaccharide extract. Papain was selected for further study because it presented the most outstanding efficiency of protein removal compared to neutral protease, chymocotrypsin, Amano protease, papain and alkaline protease. Four parameters affecting the efficiency of protein removal of papain including enzyme concentration, pH value, temperature and enzymolysis duration were investigated by one-factor-at-a-time (OFAT) experiments. The optimum ranges of the four parameters for protein removal were as follows: enzyme concentration 8 － 10 mg/g substrate, pH 7.0 － 7.5, temperature 45 － 50℃, and enzymolysis duration 120 － 150 min, and in verification experiments repeated three times a highest purity of 97.0% of the polysaccharide was observed, as well as a decrease of protein content in the crude polysaccharide from 0.91% to 0.32%. When papain was directly added to the extraction solution, a purity of 92.0% could be achieved at 4 h of extraction. The one-step extraction – purification procedure may be a more simple and rapid technique for the extraction and purification of polysaccharide from Bletilla striata roots.

Key words: Bletilla striata, polysaccharide, enzymatic purification, papain