Optimization of ultrasound-assisted extraction of phenolic antioxidants from turkey berry (Solanum torvum Sw) fruits using response surface methodology

Abstract

The extraction of phenolic antioxidants from turkey berry fruits (TBF) was evaluated using ultrasound-assisted extraction (UAE) technique. Box-Behnken design was used to optimize the extraction variables (ethanol concentration, extraction temperature, time, and solvent-solid ratio), to maximize total phenolic content (TPC), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activities of the extracts. The model significantly explained the responses and the phenolic contents and antioxidant activity were significantly influenced by ethanol concentration, extraction temperature, and solvent-solid ratio. The optimum UAE conditions for achieving maximum TPC (192.3 mg GAE/g), DPPH (47.4 μg AA/g) and ABTS (116.2 μmol TE/g) scavenging activity were 56.7% ethanol concentration, 80 °C, extraction temperature, 17.3 min extraction time, and 49.7 mL/g solvent-solid ratio. The experimental values of TPC and radical scavenging activity obtained were in agreement with the predicted values. Also, the results confirmed that UAE can recover higher phenolic antioxidants from TBF in shorter time than the conventional solvent extraction (CSE) process. Furthermore, the main phenolic compounds found in the TBF extract were catechin, kaempferol, quercetin, rutin and syringic acid. Consequently, this study revealed the aptness of UAE and RSM in improving the extraction conditions of phenolic antioxidants from TBF.