Optimization of microwave extraction method of phenolic compounds from red onion using response surface methodology and inhibition of lipoprotein low-density oxidation

Abstract

In the present study, we have optimized by surface response methodology (BBD model) phenolic compounds recovery using microwave-assisted extraction (MAE) as an innovative technique. The extraction was carried out under different experimental conditions: ethanol/water (x1, 30–80 %), time (x2, 30–180 s), microwave power (x3, 500–900 W) and solvent to sample ratio (x4, 20:1 40:1, v/w). Total phenolics content (TPC) and antioxidant activities (AA) of onion extract were investigated on 2,2−9-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS+)radical dot, 1,1-diphenyl-2-picrylhydrazyl radical (DPPHradical dot), oxygen radical absorbance capacity (ORAC) tests, and on biological model oxidation, human low-density lipoprotein (LDL). The maximum predicted TPC under the optimal MAE conditions (70 % ethanol), 700 W microwave power, 65 s extraction time and 25 mL g–1 solvent to solid ratio), was 10.90 ± 0.88 mg GAE g–1 DW. The AA of MAE or conventional extraction (CE) extract showed similar activities to neutralize DPPH, ABTS or AAPH derived radicals. The modified Gompertz model has been successfully used to describe CDs production kinetic in LDL Cu2+-mediated oxidation. This allowed the estimation of the lag time (Tlag) and the oxidation propagation rate (Rp) with precision. LDL oxidation assay showed that red onion extract increased significantly Tlag and giving an increased protection ratio at higher concentration (2.95 μmol L−1) of 180 % and 172 % for MAE and CE methods, respectively. However, Rp and CDs production remained constant. Results showed that microwave used for extraction does not affect the composition and antioxidant properties of onion sample. Red onion may be an important source of bioactive compounds and could promote health consumers.