Abstract: In order to enhance the physiological function of garlic straw dietary fiber,the different extraction methods on the soluble dietary fiber （Soluble dietary fiber,SDF） content were studied. Taking SDF content as the response value,the modification effects of ultrasound,enzymatic hydrolysis and ultrasonic complex enzymatic hydrolysis were compared and analyzed,and the effects of solid-liquid ratio,ultrasound time,ultrasound power,enzyme amount and enzymatic hydrolysis time on the yield of SDF were studied. The antioxidant capacity of SDF in vitro was evaluated by the clearance rate of hydroxyl（·OH） and 1,1-diphenyl-2-amylhydrazine free radicals （DPPH·）. The results suggested that when garlic straw was pretreated by ultrasonic assisted enzymatic hydrolysis method,the SDF yield was the highest. The optimal extraction conditions consisted of solid/liquid ratio of 1∶30, ultrasonic power of 300 W,ultrasonic time of 15 min,E/S ration of 5% and enzymatic hydrolysis of 4 h. The IC₅₀ of SDF on OH· and DPPH· were obtained to be 1.41 and 0.64 mg/mL, respectively. Moreover,the relationship between free radical scavenging rate and SDF concentration was linear, suggesting that SDF was a good antioxidant.

Key words: garlic straw, soluble dietary fiber, ultrasound, enzymatic hydrolysis