Fractionation, characterization and anti-fatigue activity of polysaccharides from Brassica rapa L.

Limited information is available on polysaccharides in Brassica rapa L. (BRP) cultivated at the plateau with an altitude over 3000 m. In the present study, an efficient ultrasonic-assisted extraction (UAE) procedure for polysaccharides from Brassica rapa L. was investigated and optimized by response surface methodology (RSM). Based on the optimal extraction parameters, gradient ethanol precipitation was used as the purification procedure of BRPs, obtaining four fractions named as BRP-20, BRP-40, BRP-60, and BRP-80, respectively. The four fractions presented different physicochemical properties and antioxidant activities. According to the chemical composition detection and monosaccharide compositions analysis, the uronic acids contents of BRP-40 and BRP-60 were higher than the other two fractions. The results of monosaccharide composition suggested that these four fractions were all heteropolysaccharides, consisted of rhamnose, xylose, mannose, glucose, galactose, galacturonic acid, and glucuronic acid. Furthermore, BRP-80 gave the best performance in radical scavenging tests, which could attribute to its lowest molecular weight. What’s more, animal experiment suggested that BRP-80 had anti-fatigue and antioxidant activity in vivo. Overall, polysaccharides from Brassica rapa L. might be developed as a novel source of natural antioxidant and be a potential candidate of anti-fatigue dietary supplements.