Abstract:This paper studied the extraction process and antioxidant activity of total triterpenoids from Qinghai Nostoc commune.Single factor test and Box-Behnken response surface test were used to optimize the ultrasonic-assisted extraction process of total triterpenoids from N.commune，and the scavenging ability of total triterpenoids on DPPH，ABTS+，and hydroxyl free radicals and the total reducing ability were determined to evaluate their antioxidant activity in vitro.The optimal extraction conditions were as follows:solid-liquid ratio 1∶20（g/mL），ethanol concentration 95%，extraction temperature 60 ℃ and extraction time 50 min.Under these conditions，the yield of total triterpenoids from N.commune was 1.38%，which was basically consistent with the predicted value of 1.41%.The antioxidant test showed that the DPPH free radical scavenging rate reached the maximum of 48.43% when the concentration of total triterpenoids was 1.60 mg/mL.The ABTS+free radical scavenging rate increased with the increase of concentration，and when the concentration was 3.20 mg/mL，the ABTS+free radical scavenging rate reached the maximum of 81.43%.There was no obvious linear relationship between hydroxyl free radical scavenging rate and concentration.The total reducing ability of total triterpenoids from N.commune increased with the increase of concentration，and when the concentration was 3.20 mg/mL，the total reducing ability reached1.818.The above results indicated that response surface methodology was reasonable and feasible to optimize the extraction conditions of total triterpenoids from N.commune，and the total triterpenoids from N.commune had high antioxidant activity.