Total polyphenols from Solanum retroflexum Dun. fruit: extraction and optimization by response surface methodology

Total phenolic (TPC), flavonoid (TFC) content and antioxidant activity (AOA) of Solanum retroflexum fruit extracts obtained by conventional extraction with different aqueous ethanol solution (25, 50, 75% v/v), temperatures (20, 40, 60 °C) and extraction time (15, 30 and 45 min) were investigated. The extract obtained by 75% aqueous ethanol at 60 °C after 45 min shows the highest AOA determined by DPPH (EC50 = 60.67 mg/ml) and FRAP (1.55 µmol Fe2+/mg) methods. TPC and TFC were in ranges from 63.50 ± 0.43 to 92.07 ± 1.07 mg of gallic acid/g of dry extract and from 29.17 ± 0.35 to 48.22 ± 0.43 mg of rutin/g of dry extract, respectively. In order to commercialize the extraction of polyphenolic compounds, as the most important group of the plant bioactive compounds, the extraction conditions were optimized by response surface methodology. Under proposed optimum extraction conditions (60 °C, 40.3 min and ethanol concentration of 74.7%) extract with the maximal TPC (92.29 mg gallic acid/g of dry extract) could be obtained. The set of the extraction conditions which gave the maximum TPC while simultaneously minimizing the time, energy and ethanol consumption were also proposed (economic extraction conditions). The results confirm that this insufficiently tested fruit represent a good source of polyphenolic compounds and are worthy of further investigation.