Ultrasound-assisted extraction and antioxidant activity of polysaccharides from Acanthus ilicifolius

In the present study, ultrasound-assisted extraction of water-soluble polysaccharides from the Acanthus ilicifolius was optimized by using one-factor-at-a-time and Box–Behnken designs. A maximum polysaccharide yield of 2.46% was obtained under the optimized conditions of ultrasonic power of 150 W, temperature of 53 °C, extraction time of 50 min, and liquid to solid ratio of 35 mL/g. Results of UV, FTIR and molecular weights indicated that there were significant differences in structures of polysaccharides extracted with ultrasound assistance (UAE-ACI) and hot-water extraction (HWE-ACI) including monosaccharide compositions and ratios, and molecular weight distributions. Further analysis showed that UAE-ACI had a higher antioxidant activity in vitro than that of HWE-ACI possibly due to lower molecular weight and higher content of phenolics and protein fractions.