Optimization of Solid-Liquid Extraction of Antioxidants from Black Mulberry Leaves by Response Surface Methodology

The extraction of active components from natural sources depends on different factors. The knowledge of the effects of different extraction parameters is useful for the optimization of the process, as well for the ability to predict the extraction yield. The aim of this study is to examine the influence of solvent concentration (ethanol/water 40–80 %, by volume), temperature (40–80 °C) and solvent/raw material ratio (10–30 mL/g) on the extraction yield of phenolic compounds, flavonoids and antioxidant activity from black mulberry (Morus nigra L.) leaves. Experimental values of total phenolic content were in the range from 18.6 to 48.7 mg of chlorogenic acid equivalents per g of dried leaves and total flavonoids in the range from 6.0 to 21.4 mg of rutin eqivalents per g of dried leaves. Antioxidant activity expressed as the inhibition concentration at 50 % (IC50 value) was in the range from 0.019 to 0.078 mg of mulberry extract per mL. Response surface methodology (RSM) was used to determine the optimum extraction conditions and to investigate the effect of different variables on the observed properties of mulberry leaf extracts. The results show a good fit to the proposed model (R˄2>0.90). The optimal conditions for obtaining the highest extraction yield of phenolics and flavonoids were within the experimental range. The experimental values agreed with those predicted, thus indicating suitability of the used model and the success of RSM in optimizing the investigated extraction conditions.