Comparative evaluation of maceration and ultrasonic-assisted extraction of phenolic compounds from fresh olives

Ultrasonic-assisted extraction (UAE) and maceration extraction (ME) were optimized using response surface methodology (RSM) for total phenolic compounds (TPC) from fresh olives. The main phenolic compounds and antioxidant activity of TPC were also investigated. The optimized result for UAE was 22 mL/g of liquid-solid ratio, 47 °C of extraction temperature and 30 min of extraction time, 7.01 mg/g of yielding, and for ME was 24 mL/g of liquid-solid ratio, 50 °C of extraction temperature and 4.7 h of extraction time, 5.18 mg/g of yielding. The HPLC analysis revealed that the extracts by UAE and ME possessed 14 main phenolic compounds, and UAE exhibited more amounts of all phenols than ME. The most abundant phenolic compounds in olive extracts were hydroxytyrosol, oleuropein and rutin. Both extracts showed excellent antioxidant activity in a dose-dependent manner. Taken together, UAE could effectively increase the yield of phenolic compounds from olives. In addition these phenolic compounds could be used as a potential source of natural antioxidants.