Optimization of ultrasonic-assisted extraction of phenolic compounds from bovine pennyroyal (Phlomidoschema parviflorum) leaves using response surface methodology

The ultrasound-assisted extraction (UAE) was applied to optimize the experimental conditions for the extraction of phenolic compounds from bovine pennyroyal (Phlomidoschema parviflorum) leaves by response surface methodology (RSM) and to compare its efficiency with maceration extraction (ME). The Box-Behnken design was employed for the optimization of three extraction parameters, including extraction time (X-1, min), temperature (X-2, degrees C) and pH (X-3) for the achievement of high yields of dry matter (DM), total phenolics (TP) and antioxidant activity (AA) measured by the DPPH assay [expressed as 50% effective concentration (EC50)] and the Rancimat method [expressed as induction period (IP)]. The optimum extraction conditions were as follows: extraction time 49.3 min, extraction temperature 41.5 degrees C and pH 6.5. Under these conditions, DM, TP, EC50 and IP were 25,185 mg/kg sample, 15.4 mg GAE/g DM, 0.48 mg/ml and 5.7 h, respectively. The comparison between the UAE and ME methods showed the suitability of UAE for extracting phenolic compounds from bovine pennyroyal plant. The evaluation of antioxidant activity by DPPH assay indicated that the phenolic compounds from bovine pennyroyal plant had significant antioxidant activity. The results of HPLC analysis showed that caffeic acid and quercetin were the predominant phenolic acid and flavonoid in the plant extract, respectively. (C) 2014 Elsevier B.V. All rights reserved.