Ultrasound-Assisted Extraction of Polyphenols from Laurus nobilis Leaves: Effects of Process Parameters

Due to the increasing demand for herbal supplements, this study investigates the effects of the ultrasound-assisted extraction (UAE) parameters (amplitude, time and temperature) on the extraction of polyphenols from laurel leaves, as this method enables the production of a range of extracts in a shorter time. UAE affects the colour of the extracts when an amplitude of 60, 80 and 100%, a time period of 3, 6 and 9 min and acetone or ethanol (30 and 70%, v/v) are used. The solvent had the greatest influence on the colour of the extract, which was positively related to the parameters b and ΔE (Std. Coeff. = 0.9696 and 0.9354) and negatively related to the values a and L (Std. Coeff. = −0.9741 and −0.5733). The solvent also influenced the recovery of total phenols and flavonoids, as well as most phenolic compounds. The highest levels of phenols and flavonoids were determined for 70% ethanol (28.04 and 10.73 mg/g) and 70% acetone (32.10 and 12.13 mg/g) at an amplitude of 100% for 9 min. Meanwhile, 70% ethanol at an amplitude of 100% for 9 min gave the highest amount of rosmarinic acid, with values of 216.32 mg/L, showing that it dominates among the phenolic compounds.