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Optimization of the Extraction of Total Phenols from Medicago sativa and Its Antioxidant Capacity

The phenolic compounds from alfalfa (Medicago sativa L.) are used as antioxidants and in native medicine. They play an indispensable role in defense and signal transduction of the plant under stress conditions. This exploration of the optimal extraction parameters of the total phenols from alfalfa by using ultrasonic‐assisted extraction (UAE) was aimed at providing a theoretical basis for better utilization of the total phenols in alfalfa. In this study, the effects of solvent volume fraction (A), extraction time (B), solid‐liquid ratio (C) and extraction temperature (D) on the total phenols content and the total antioxidant capacity of Medicago sativa L. WL363HQ after thrips infestation were determined through single‐factor experiments. Additionally, the extraction conditions of total phenols were optimized by using Box‐Behnken design (BBD) of response surface methodology (RSM). The results showed that the proposed model had a good fitting degree for total phenols extraction (R2=0.9564). The total phenols extraction from WL363HQ had significant relationship with solid‐liquid ratio (C) and extraction temperature (D) (P<0.05). The influence levels of the four factors on total phenols extraction were as follows: extraction temperature (D) > solid‐liquid ratio (C)>acetone volume fraction (A)>extraction time (B). The optimum extraction conditions of total phenols from WL363HQ were 50 % acetone, solid‐liquid ratio of 1 : 20 (g/mL), extraction time of 45 min and extraction temperature of 60 °C. The corresponding content and total antioxidant capacity under the optimized conditions were 15.76 mg g−1 and 28.79 μmol Trolox g−1. These results provided a new extraction method of total phenols from alfalfa.