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Optimization of Ultrasonic Extraction of Total Flavonoids from Litchi (Litchi chinensis Sonn.) Seed by Response Surface Methodology

The ultrasonic technology was applied to optimize the processing parameters of extraction of flavonoids from litchi seed using the response surface methodology. The Box–Behnken design was used to analyze the effect of independent variables including extraction temperature (X1), methanol concentration (X2) and extraction time (X3) on the yield of total flavonoids as the dependent variable(Y). The analysis of variance (ANOVA) indicated that three independent variables, their quadratic terms and interaction terms showed a significant effect on yield of total flavonoids (YTF) except the interaction between X1 and X2. A mathematical model with high determination coefficient was constructed, according to which the optimal extraction conditions were determined as follows: extraction temperature 70°C, methanol concentration 68%, extraction time 70 min. Under the above-mentioned condition, the experimental value of YTF was 3.55 g catechin equivalent per 100 g of dry (g CE/100 g ), which agreed with the predicted value perfectly, demonstrating the response surface model was suitable in optimizing the extraction of flavonoids from litchi seed.