Abstract:

In this experiment, the optimal extraction process and antioxidant capacity of total flavonoids from alfalfa (Medicago sativa L.) were studied. Orthogonal experiment was designed based on the single factor experiment, and the optimal extraction process was determined by analysis of variance and multiple comparisons. The in vitro antioxidant activities of total flavonoids were evaluated by measuring scavenging rate of 1,1-dipheny l-2-phenyl-free radical(DPPH·)and reducing force. The optimal extraction conditions were:the ethanol volume fraction 70%,the extraction temperature 60℃,extraction time 30 min and the ultrasonic power was 180 w,total flavonoids yield was 6.43 mg·g^-1. The total flavonoid from alfalfa leaf had obvious antioxidant activity in a certain concentration range, and the antioxidant activity was increased with the increase of mass concentration. The total flavonoids from alfalfa leaf had strong reducing power, the half inhibitory concentration (IC₅₀) of DPPH radical was 0.608 mg·mL^-1. Ultrasonic assisted extraction process of total flavonoids from alfalfa leaves is a highly efficitent way. This optimized process is economical,reasonable and stable.

Key words: Alfalfa leaf, Total flavonoids, Ultrasonic extraction, Antioxidant activity

摘要：

研究紫花苜蓿（Medicago sativa L.）叶总黄酮的最优提取工艺及体外抗氧化能力。在单因素试验的基础上设计正交试验，通过方差分析和多重比较确定最优提取工艺。以1，1-二苯基-2-三硝基苯肼（2，2-diphenyl-1-picrylhydrazyl，DPPH）清除率测定法及还原力测定法评价苜蓿黄酮类化合物体外抗氧化活性。最佳提取工艺条件是：乙醇体积分数70%、提取温度60℃、提取时间30 min、超声功率180 w，总黄酮得率为6.43 mg·g^-1。苜蓿叶总黄酮在一定的质量浓度范围具有较明显的抗氧化活性，并随着质量浓度的增加活性增强。苜蓿叶总黄酮具有较强的还原力，清除DPPH自由基的半数抑制质量浓度（IC₅₀值）为0.608 mg·mL^-1。超声提取是一种高效的提取紫花苜蓿叶总黄酮方法。超声优化的苜蓿叶总黄酮提取工艺经济、稳定、合理可行。

关键词: 紫花苜蓿叶, 总黄酮, 超声波辅助提取, 抗氧化活性