Optimization of ultrasound assisted extraction method for phytochemical compounds and in-vitro antioxidant activity of New Zealand and China Asparagus cultivars (officinalis L.) roots extracts

摘要

A two-level Plackett-Burman design with 8 variables was used to evaluate ultrasonic treatment variables influencing the total phenolic content (TPC) extracted from asparagus roots. Steepest ascent method was conducted to identify the significance of parameters such as extraction temperature, stirring speed, intermission time, extraction time, ultrasonic frequency, and ultrasonic power. Ethanol and methanol aqueous solutions were used as extraction solvents and solvent's concentration, extraction time, ultrasonic power and solid: liquid ratio were optimized in this study. A predicted value of TPC (71.1 mg/g) was obtained under the optimum conditions of extraction time 120 min, ultrasonic power 550 W, ethanol concentration of 20% and a solid: liquid ratio of 1:100. Central composite design was employed to further analyse the common interactions between the extraction variables and to further determine the optimal values that would generate the maximum TPC, total flavonoids content, total saponins content, caffeic acid and in vitro antioxidant activities. The optimal variables for ethanol extraction (80 min, 50% of ethanol, 360 W and 1:40) generated higher than methanol (410 W for 114.9 min using 73.7% methanol at 1:24).