Intensification of bioactive compounds extraction from Feijoa (Feijoa sellowiana Berg.) leaves using ultrasonic waves

In this study, ultrasound-assisted extraction (UAE) of bioactive compounds from Feijoa sellowiana leaves was optimized using response surface methodology. Box-Behnken design was applied to evaluate the effects of ultrasonic intensity, duty cycle and extraction temperature on crude extraction yield (CEY) and radical scavenging activity (RSA) in terms of inhibition of DPPH, OH and ABTS+ radicals. The correlation analysis of mathematical-regression models indicated that quadratic polynomial models could be employed to optimize UAE process. Under the optimal conditions (1569.10 W/cm2, 89.00% and 46.00 °C) the predicted values of the CEY and RSA of DPPH, OH and ABTS+ were 53.22 mg g−1, 78.43%, 62.00% and 81.54%, respectively. High-performance liquid chromatography (HPLC) analysis showed that gallic acid, catechin, ferulic acid, quercetin and apigenin are the major phenolic compounds existed in the extracts. The improvement of UAE was investigated by combining pre-leaching stage (PLS) with optimized UAE conditions (PLS-UAE). Spectrophotometric methods and HPLC analysis results revealed that the bioactive phenolic compounds increased using PLS-UAE, where gallic acid had the highest concentration (123.15 ± 0.34 mg g−1). The comparative study results, which has been done between optimized UAE, PLS-UAE and conventional Soxhlet extraction (CSE) revealed that higher CEY (81.11 ± 0.11 mg g−1) could be achieved using CSE even through, the quality of extracts in terms of phenolic compounds and RSA was significantly (p-value < 0.05) higher using optimized UAE and PLS-UAE. Scanning electron microscopy (SEM) images showed that PLS-UAE can significantly damage the structure of vegetal tissues leads to improved extraction of bioactive compounds.