Abstract:

The extraction of flavonoids from leaves of Lonicera japonica Thunb. (L. japonica) was optimized by the
combined use of single factor experiments and response surface methodology. For this purpose, a second-order rotation
combination experimental design was conducted using ethanol concentration, extraction temperature, ratio of solvent to
materials and ultrasonic power as the independent variables. The in vitro antioxidant activity of the obtained flavonoids
was studied. Results indicated that the highest yield of flavonoids of 15.67% was achieved when the extraction was carried
out with an ultrasonic power of 250 W using 60% ethanol as the extraction solvent at a solvent/solid ratio of 65:1 (mL/g),
which was in good agreement with the model predicted value. Antioxidant tests showed that the flavonoids extracted from
the leaves of L. japonica possessed strong antioxidant ability, and the superoxide anion free radical scavenging capacity was
negatively correlated with reaction time but positively correlated to their concentration. The IC50 for scavenging hydroxyl
radical was 0.11 mg/mL, a 34-fold increase over that of control.

Key words: Lonicera japonica Thunb. leaves, flavonoid, ultrasonic-assisted extraction, quadratic general rotation combination design, antioxidant capacity