Evaluation of the ethanolic ultrasound-assisted extraction from clove (Syzygium aromaticum) leaves and chemical characterization of the extracts

•Extraction of clove leaves by ultrasound-assisted method with ethanol.•Evaluation of time, amplitude, solvent/leaves ratio, and temperature on the yield.•Quantification of the eugenol compound in the extracts by HPLC.•Evaluation of total phenolic content and antioxidant activity by DPPH and FRAP.•Ultrasound method increased the yield up to ∼62% in relation to the maceration. In this study, clove leaves (Syzygium aromaticum) were subjected to ultrasound-assisted extraction (UAE) with ethanol as the solvent, following a central composite design to evaluate the effects of time, amplitude, solvent/sample ratio, and temperature on the yield, eugenol content, and antioxidant capacity of the extracts. The results were compared with those obtained using the conventional method of maceration (ME). The optimum conditions for extract yield were achieved with an extraction time of 25 min,amplitude of 85%, solvent/sample ratio of 35 mL g−1, and temperature of 70 °C, and the result (14.63 wt%) was three times higher than that of conventional extraction. Eugenol was detected in the extracts obtained by both methods, with the highest yield of 2.94 g eugenol kg leaves−1obtained in the UAE method, while the ME method achieved 1.36 g eugenol kg leaves−1.In general, the extracts exhibited high antioxidant capacities.