Abstract: The purpose of this work was to study extraction conditions and antioxidant activity in vitro of capsular polysaccharide (CP) from Lactobacillus helveticus MB2-1, a potent CP producing strain isolated from Sayram traditional yogurt from Xinjiang. After 18 h of hydrolysis with both pepsin and trypsin at a total dosage of 1400 U/mL under the conditions of 37 ℃ and pH 6.0, the yield of CP was 184.58 mg/L and the resulting extract contained 95.58% polysaccharide and 1.82% protein. At 4.0 mg/mL, it had strong scavenging activities against DPPH and hydroxyl free radicals with corresponding scavenging rates of 84.30% and 48.22% and powerful reducing power (83.88%) and ferrous ion-chelating capacity (35.68%).

Key words: Sayram yohurt, Lactobacillus helveticus MB2-1, capsular polysaccharide, extraction, antioxidant capacity