Optimization of ultrasonic extraction of polysaccharides from Flammulina velutipes residue and its protective effect against heavy metal toxicity

Abstract

The extraction process of polysaccharides from Flammulina velutipes residue (FVRP) was optimized by the single factor test and response surface methodology with the physical and chemical properties of FVRP determined. The protective effect of FVRP against heavy metals and their mechanism were studied based on Saccharomyces cerevisiae. The results showed that the extraction rate reached 83.7 mg/g with conditions as follows: ultrasonic temperature 75 ℃, extraction time 20 min, material-liquid ratio 1:50 (g/mL), and ultrasonic power 540 W. FVRP with an average molecular weight of 335.3 kDa, containing xylose (17.2 %), galactose (17.0 %), mannose (15.8 %), fucose (9.3 %), arabinose (5.7 %), rhamnose (7.4 %), glucose (8.3 %), galacturonic acid (16.2 %), and glucuronic acid (3.3 %), was obtained under the optimal conditions. FVRP exhibited a strong in vitro antioxidant activity, the scavenging rate on DPPH and ABTS was 55.6 % and 93.9 %, respectively, as FVRP concentration reached 4 mg/mL. Moreover, FVRP significantly rescued the toxicity of heavy metals (cadmium, nickel, and lead) and H2O2 in yeast cells by reducing the overproduction of intracellular reactive oxygen species (ROS). Furthermore, FVRP at the concentration of 0.1 mg/mL still exhibited protective effect in yeast cells against toxicity. Our study built a strong foundation for the reuse and development of FVRP and its protective effect against heavy metal toxicity.