Optimization and comparative evaluation of ultrasound-assisted extraction of bioactive phenolic compounds from feijoa (Feijoa sellowiana) leaves

In this study, the effect of ultrasound-assisted extraction (UAE) process independent variables including ultrasonic intensity (714.00, 1425.50 and 2143.00 w cm-2), duty cycle (50, 75 and 100%) and extraction temperature (30, 45 and 60 °C) on feijoa leaves bioactive phenolic compounds was investigated and optimized using response surface methodology based on Box-Behnken design. The total phenolic content of extracts was measured using Folin- Ciocalteu method. Quadratic polynomial model was obtained for total phenolic compounds using multiple linear regression analysis. The optimal conditions were determined as 1749.34 W cm-2 ultrasonic intensity, 86.39% duty cycle and 32.49 °C extraction temperature. The radical scavenging activity of phenolic compounds obtained under optimized UAE conditions was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2´-Azinobis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) radical scavenging activity methods. Based on results obtained, the total phenolic compound and radical scavenging activity of extract obtained under optimal conditions were 381.20 ± 0.12 mg GAE/g, 81.43 ± 0.10% of DPPH radical inhibition and 86.63 ± 0.26% of ABTS radical inhibition, respectively. The model obtained for prediction of dependent variable has a good closeness with experimental results. The agitated bed extraction technique was investigated to carry out the comparative evaluation. The effect of agitation intensity (50-300 rpm) on total phenolic content of extracts obtained using this technique was studied. Based on results obtained, the highest value of total phenolic content (352.95 ± 0.12 mg GAE/g) could be achieved using 200 rpm agitation intensity. The radical scavenging activity of extract was 73.33 ± 0.16% of DPPH radical inhibition and 82.20 ± 0.12% of ABTS radical inhibition. According to the results obtained it could be stated that ultrasound-assisted extraction is a promising technique to obtain extracts contain more phenolic compounds and higher radical scavenging activity during short extraction time.