Optimization of Ultrasound-Assisted Extraction Procedure to Determine Antioxidant Capacity of Rapeseed Cultivars - Food Analytical Methods

Ultrasound-assisted extraction (UAE) was applied to extract total antioxidants from two rapeseed varieties. The antioxidant capacity of spring and winter rapeseed cultivars was determined by two different analytical methods: 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and 2,2′-diphenyl-1-picrylhydrazyl (DPPH). Effects of three independent variables, sonication time (t), volume of methanol-to-rapeseed weight ratio (V/m), and concentration of methanol (c) on the antioxidant capacity of rapeseed varieties, were studied by response surface methodology (RSM). Box–Behnken design (BBD) was used to obtain the optimal conditions of the UAE. The optimal UAE conditions were evaluated with an extraction time of 13.8 min, a solvent-to-material ratio of 26.2 mL/g and a solvent concentration of 50.3 % for antioxidant capacity of spring rapeseed cultivar (ABTS = 62.7 mmol Trolox equivalent (TE)/100 g, DPPH = 38.3 mmol TE/100 g), whereas the predicted optimum t = 13.3 min, V/m = 29.5 mL/g, and c = 38.3 % resulted in ABTS = 62.0 mmol TE/100 g, DPPH = 48.6 mmol TE/100 g for a winter rapeseed cultivar. Results of ABTS and DPPH determinations correlate with the predicted values (R 2 = 0.9435 and 0.9796 for the spring rapeseed variety and 0.9952, 0.9252 for the winter rapeseed variety).