Simple and rapid procedures for the extraction of bioactive compounds from Guayule leaves

Solid liquid extraction (SLE) and ultrasound-assisted extraction (UAE) using food grade solvents were applied to
Guayule leaves in order to obtain phenolic compound-rich extracts. The influence of solvent composition and
time were evaluated for both techniques reaching the highest phenolic content with UAE using water and 25%
aqueous ethanol (27.0 ± 0.2 and 22 ± 2 mg gallic acid equivalents/g dried leaves, respectively) and with SLE
using water and 50% aqueous ethanol (16 ± 1 and 17 ± 1 mg/g, respectively). Antioxidant and antiradical
activities of the selected extracts were evaluated by means of spectrophotometric procedures. In addition HPLCESI-
QTOF-MS was used to characterize the bioactive compounds in the richest extracts. A variety of phenolic
compounds, mainly phenolic acids and flavonoids, were identified for the first time in Guayule leaves. This study
indicates that conventional extraction techniques, such as SLE and UAE, represent a powerful tool for the fast
isolation of antioxidant compounds from Guayule.