Abstract: The ultrasonic-assisted extraction of polysaccharide from Dendrobium officinale at a 250 W low power was optimized by response surface methodology based on central combination design. Extraction temperature, solvent-to-solid ratio, and ultrasonic treatment time were considered as independent variables. The optimum extraction conditions were determined as follows: extraction temperature 41.74 ℃, solvent-to-solid ratio 50.26:1 (mL/g), and ultrasonic treatment time 28.65 min. Under these conditions, the maximum extraction yield of 25.39% was obtained, which was increased by 18% compared with the value obtained using conventional hot water extraction with a simultaneous reduction in extraction time of 75%. Moreover, the DPPH and hydroxyl radical scavenging activities of polysaccharide from D. officinale were not reduced during ultrasonic-assisted extraction. Drosophila melanogaster were fed with different doses of the extracted polysaccharide, and the results showed that the polysaccharide at moderate dose provided the best antioxidant activity as evidenced by a 30% increase in superoxide dismutase (SOD) and catalase (CAT) activity and a 46% decrease in malondialdehyde (MDA) content of male D. melanogaster, as well as an increase of 60% in CAT activity and 6% in SOD activ ity and a 20% decrease in MDA content of female D. melanogaster, extending the lifespan by an average of 20%.

Key words: Dendrobium officinale, polysaccharide, ultrasonic, response surface analysis, antioxidant activity, Drosophila melanogaster