Study on ultrasonic extraction of seed watermelon polysaccharides and evaluation of its molecular weight and antioxidant activity

The seed watermelon polysaccharide was extracted from seed watermelon using ultrasonic assisted extraction technique. The three factors:extraction time, extraction temperature and solid-liquid ratio were optimized based on response surface methodology ( RSM) . The results showed that the optimum seed watermelon polysaccharides extraction conditions was:ultrasonic treatment time 85min, extraction temperature 49℃, and solid/liquid ratio 1 ∶1.7g/mL, seed watermelon polysaccharides yield reached up to 4.128%. The molecular weight of seed watermelon polysaccharides was measured using SEC-HPLC and LLS:Mn=1.089×106g/moL. According to the scavenging capacity of seed watermelon polysaccharides against radicals, it showed that the scavenging capacity of seed watermelon polysaccharides agaist DPPH radicals was 68% at the concentration of 0.01⁰.32mg/mL, higher than VCsignificantly. The scavenging capacity of seed watermelon polysaccharides agaist hydroxyl radicals was 75.35% at the concentration of 5mg/mL and the scavenging capacity of superoxide radicals was 50% at the same concentration. The result showed that seed watermelon polysaccharides had strong free radical-scavenging capacity. And could be use as a potential natural antioxidant in the food and pharmaceutical industry.