Ultrasound-assisted extraction of phenolic compounds from avocado leaves (Persea americana Mill. var. Drymifolia): optimization and modeling

Ultrasonic-assisted extraction (UAE) was performed to extract the total phenolic compounds from avocado ( Mill. var. Drymifolia; Lauraceae) leaves with different electric powers (UAE 0%, UAE 60%, and UAE 100%) and extraction times. Ultrasonic extraction parameters were optimized by using a mathematical model made by stepwise regression (SWR) for the determination of the maximum total phenolic content (TPC) and their antioxidant activity. Moreover, TPC extraction was modeled applying heterogeneous models to elucidate the involved mechanisms phenomena that determine the extraction rates. Optimization results found that the maximum value of TPC reached 48,732 mg GAE/100 g D.M. at 84.5% electric power and 29.7 min of extraction, which was superior to 0% electric power UAE. It was also found that the ultrasound causes the degradation of phenolic compounds, whereas the final extraction yield of TPC increases and their antioxidant activity decreased with the increase of ultrasound electric power. Proposed models gave a satisfactory quality of fit data using a second-order reaction for the degradation kinetics of TPC under ultrasound application. The estimated effective diffusivity values were in a range from 1.3889 × 10 m /s to 2.2128 × 10 m /s for the UAE 0% and UAE 100%, respectively. UAE significantly increased the extraction yield through the enhancement of the effective diffusivity, demonstrating that it is a promising technology to extract phenolic substances from avocado leaves.