Different extraction pretreatments significantly change the flavonoid contents of Scutellaria baicalensis

Figures & data

Figure 1. Chemical structures of the major flavonoids in S. baicalensis during endogenous enzymatic conversion from glycosides to aglycones. These enzymes likely are β-d-glucuronidase, β-d-glucosidase and other β-d-glycosidases. The lower portion of the figures listed the conversion of five glycosides to three aglycones.

Figure 2. Four kinetics used to evaluate the time curves of the measured four flavonoids in S. baicalensis during pure water pretreatment. (A) Empirical equation, (B) zero-order kinetics, (C) first-order kinetics, and (D) second-order kinetics. Based on Table 1 data, the first-order kinetics was chosen for Figures 3, 4, 5, and 6 observations.

Table 1. Four kinetic equations used in Figure 2.

Kinetics	Equation	Adjusted R^2	Probability (>F)	t0.5 (min)
Empirical model
Baicalin		0.9586	6.14E−4	11.16
Wogonoside		0.9012	1.30E−3	33.13
Baicalein		0.9380	3.45E−5	12.08
Wogonin		0.8884	2.46E−4	35.67
Zero order
Baicalin		0.23976	1.00E−1	86.86
Wogonoside		0.48099	1.50E−2	104.96
Baicalein		0.25019	1.50E−3
Wogonin		0.48768	1.60E−3
First order
Baicalin		0.9955	4.61E−7	11.32
Wogonoside		0.9497	5.57E−5	27.69
Baicalein		0.9796	3.74E−6
Wogonin		0.9368	7.99E−5
Second order
Baicalin		0.9448	2.36E−4	8.03
Wogonoside		0.9005	2.99E−4	24.01
Baicalein		0.9380	3.45E−5
Wogonin		0.8884	2.46E−4

The first-order kinetics was chosen since it showed the most reliable pretreatment time curves based on the values of adjusted R² and probability obtained.

Figure 3. Effects of S. baicalensis pretreatment with different initial temperature and solvent on the four flavonoid content changes. (A) Using 25 °C water for initial soaking. (B) Using 50 °C warm water for initial soaking. (C) Using 90 °C hot water for initial soaking. (D) Using 75% ethanol at 25 °C for initial soaking. After initial soaking at indicated temperature, the mixture was incubated at 50 °C for 240 min.

Figure 4. Effects of S. baicalensis pretreatment with different steady temperature on the four flavonoid content changes. Glycosides are shown in (A) baicalin and (B) wogonoside. Aglycones are shown in (C) baicalein and (D) wogonin.

Figure 5. Effects of S. baicalensis pretreatment with different herb/water (in w/v) ratio on four flavonoid content changes. Glycosides are shown in (A) baicalin and (B) wogonoside. Aglycones are shown in (C) baicalein and (D) wogonin.

Figure 6. Effects of S. baicalensis pretreatment with different pH values on four flavonoid content changes. Glycosides are shown in (A) baicalin and (B) wogonoside. Aglycones are shown in (C) baicalein and (D) wogonin.