响应面法优化甜叶菊残渣中总黄酮提取工艺及抗氧化活性

研究甜叶菊残渣中总黄酮的提取工艺，同时测定甜叶菊残渣中总黄酮的抗氧化活性。首先以乙醇体积分数、超声功率和超声时间为因素进行单因素试验，找到每个因素的较优水平，然后在此基础上采用Box-Behnken法进行试验设计，并进行响应面分析，得到提取工艺的数学模型，预测出最佳提取工艺及最高总黄酮浸提量。结果显示：甜叶菊残渣中总黄酮物质的最佳提取工艺为乙醇体积分数70%、超声功率420 W、超声时间42 min，此时总黄酮浸提量为5.928 mg/g，与由数学模型得到的理论值5.949 mg/g基本符合。抗氧化实验结果表明，甜叶菊残渣中总黄酮具有很强的清除1,1-二苯基-2-三硝基苯肼自由基和·OH的能力，其半抑制浓度（EC50）相应为7.096、22.065 μg/mL，分别是VC的1.37、1.61 倍，表明甜叶菊残渣中黄酮类化合物有很好的抗氧化能力。

Total Flavonoids from Stevia rebaudiana Residue: Optimization of Extraction Process by Response Surface Methodology and Antioxidant Activity Evaluation

In this experiment, we optimized the conditions for extracting total flavonoids from stevia (Stevia rebaudiana)
residue left after stevioside extraction and determined the antioxidant activity of the total flavonoids. Firstly, we selected
ethanol concentration, ultrasound power, and ultrasound treatment time as factors to conduct single factor investigations for
the purpose of establishing the appropriate levels for each of these factors. Then, we developed a predictive mathematical
model of the yield of total flavonoids using Box-Behnken experimental design for the optimization of extraction conditions
by response surface analysis. The optimal extraction conditions were determined as follows: ethanol concentration, 70%;
ultrasound power, 420 W; and ultrasound treatment time, 42 min. Experiments conducted under these conditions gave the
maximum yield of total flavonoids of 5.928 mg/g, which was close to the predicted value of 5.949 mg/g. Moreover, antioxidant
experiments showed that total flavonoids from stevia residue left after stevioside had very strong scavenging capabilities for DPPH
and hydroxyl radicals with EC50 values of 7.096 and 22.065 μg/mL, respectively, which were approximately 1.37 and 1.61 times
that of vitamin C, respectively. Therefore, the total flavonoids had strong antioxidant capacity.