Microwave-assisted deep eutectic solvent extraction of phenolic antioxidants from onion (Allium cepa L.) peel: a Box-Behnken design approach for optimization

Valorization of onion peel waste, considered to be a rich source of polyphenolic compounds, by employing green extraction techniques is the need of the hour. The aim of the present study was to optimize the microwave-assisted extraction of bioactive phenolic compounds from onion peel wastes employing ChCl:Urea:H2O deep eutectic solvent. Microwave power (100-200-300 W), time (5-15-25 min) and liquid to solid ratio (40:1-50:1-60:1) were studied as the major parameters affecting the extraction efficiency. A Box-Behnken design was adopted including 17 experiments with five centre points. The optimum conditions determined were 100 W microwave power, 15.03 min irradiation time and 54.97 mL g(-1) liquid to solid ratio. Under the MAE optimized conditions, the recovery of TPC and FRAP were 80.45 (mg GAE g(-1) dw) and 636.18 (mu mol AAE g(-1) dw), respectively. Morphology of onion peels before and after DES extraction were also studied to gain an insight in the effect of microwave irradiations on the biomass.