Abstract
Six bioactive flavonoids, including apigenin, baicalein, baicalin, luteolin, naringenin and wogonin, were extracted from a herbal tea plant, Scutellaria barbata D. Don, using a hyphenated procedure (HUAE) combining heat-reflux extraction (HRE) and ultrasonic-assisted extraction (UAE); the flavonoids were analyzed by high-performance liquid chromatography–mass spectrometry (HPLC/MS). HUAE had the highest flavonoid yield, which was 8.1–9.2% and 18.3–21.1% higher than those of UAE and HRE, respectively, while using shorter extraction times (less than 45 and 165min) and less extraction solvent (less than 100 and 220mL). The enhancement of the extraction efficiency obtained by HUAE was mainly due to the combined cavitation, mechanical and thermal effects caused by the ultrasonic energy. It was further found that the experimental data obtained for the total extract of S. barbata via the HUAE and HRE procedures can achieve excellent correlation using the second-order rate model. The second-order rate constant obtained by the HUAE correlation decreased with increasing temperature, which was completely opposite to that of the HRE procedure. However, the remaining two related parameters (the equilibrium concentration of analytes and the initial extraction rate), whether obtained through HUAE or HRE procedures, increased with increasing temperature. In addition, this study also relied on the evaluation of the extraction activation energy and thermodynamic parameters to explain and demonstrate the superiority of the HUAE procedure for the extraction of S. barbata.
Published Version
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