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HQT can be derived from several Scutellaria species. S. baicalensis is the most extensively cultivated, with a significant biomass in its aerial parts. Consequently, the primary source of HQT is the aerial part of S. baicalensis, and research focused on these aerial parts is also the most extensive.
The aerial part and the root of S. baicalensis share similarities in their primary constituents, notably the significant presence of flavonoids, which are regarded as the main active components. However, there are specific chemical differences between the above-ground and underground parts of S. baicalensis. Our preliminary experiments have revealed the disparities in chemical composition between these two parts[18]. Notably, the root of S. baicalensis finds its primary use in medicinal applications, characterized by notably higher expression levels of specific 4′-deoxyflavones compared to the aerial organs. In contrast, the above-ground parts of the plant are employed to prepare tea. This differentiation in utilizing these plant components reflects the accumulated wisdom of generations cultivated through extensive periods of tasting and experience.
This section provided an in-depth review of the chemical composition of the plant from which HQT is derived. Additionally, a specific emphasis on reviewing the aerial parts of S. baicalensis, which serve as the primary source of HQT has been placed.
Flavonoids
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In the 1970s, researchers began to study the chemical composition of the aerial parts of S. baicalensis. The flavonoids are the most abundant chemical components in the aerial parts (flowers, stems, and leaves), and about 54 flavonoid compounds were identified (Table 1, Fig. 2). Most of them are flavonoids, dihydro flavonoids, and glycosides. The main glycoside-forming sugars are arabinose, glucose, and glucuronide, with the most abundant glucuronide glycosides. The optimization of extraction processes can yield a remarkable total flavonoid content of up to 5% in the stems and leaves of S. baicalensis[19].
Table 1. Flavonoids of HQT.
Number Name Formula Species Ref. 1 2',5-Dihydroxy-3',6,7,8-tetramethoxyflavone C19H18O8 S. baicalensis [17] 2 2',6-Dihydroxyflavone C15H10O4 S. baicalensis [16] 3 3',4',5,5',7-Pentamethoxyflavone C20H20O7 S. baicalensis [16] 4 4',5-Dihydroxy-3',5',6,7-tetramethoxyflavone C19H18O8 S. baicalensis [22,27] 5 4',5-Dihydroxy-7-methoxyflavanone C16H14O5 S. baicalensis [16] 6 5,4′-Dihydroxy-6,7,8,3′-tetramethoxyflavone C19H18O8 S. baicalensis [17] 7 5,2′-Dihydroxy-6,7,8-trimethoxyflavone C18H16O7 S. baicalensis [17] 8 5,2′-Dihydroxy-6,7,8,3′-tetramethoxyflavone C19H18O8 S. baicalensis [17] 9 5,2′-Dihydroxy-7,8-dimethoxyflavone C17H14O6 S. baicalensis [17] 10 5,2′-Dihydroxy-7,8,6′-trimethoxyflavone C18H16O7 S. baicalensis [17] 11 5,6,7,3',4'-Pentahydroxyflavone-7-O-glucuronide C21H20O13 S. baicalensis [13] 12 5,6,7,4'-Tetrahydroxydihydroflavone C15H12O6 S. baicalensis [17] 13 5,6,7-Trihydroxy-4'-methoxyflavone C16H12O6 S. baicalensis [15] 14 5,7-Dihydroxy-6-methoxyflavanon C16H14O5 S. baicalensis [17] 15 5,7,4′-Trihydroxy-6-methoxyflavanone C16H14O6 S. baicalensis [22] 16 5,7,4'-Trihydroxyflavanone C15H12O6 S. baicalensis [13] 17 (2S)-5,7,8,4'-Tetrahydroxyflavanone 7-O-β-D-glucuronopyranoside C21H20O12 S. baicalensis [21] 18 (2S)-5,6,7,4'-Tetrahydroxyflavanone 7-O-β-D-glucuronopyranoside C21H20O12 S. baicalensis [21] 19 6-Hydroxyluteolin-7-O-glucuronide C21H18O13 S. baicalensis [13] 20 7-Methoxychrysin C16H14O4 S. baicalensis [16] 21 Apigenin C15H10O5 S. baicalensis, S. amoena,
S. scordifolia, S. viscidula[17,21−25] 22 Apigenin-4'-glucopyranside C21H20O10 S. baicalensis [17] 23 Apigenin-6-C-glucoside-8-C-arabinoside C26H28O14 S. baicalensis [13] 24 Apigenin-7-O-β-D-glucopyranside C21H20O10 S. baicalensis [17] 25 Apigenin-7-O-β-D-glucuronide C21H18O11 S. baicalensis, S. amoena,
S. scordifolia[13,23,24] 26 Apigenin-7-O-methylglucuronide C22H20O11 S. baicalensis [28] 27 Baicalein C15H10O5 S. baicalensis, S. amoena,
S. scordifolia, S. viscidula[22−25] 28 Baicalein-7-O-D-glucopyranside C21H20O10 S. baicalensis [22] 29 Baicalin C21H18O11 S. baicalensis, S. amoena,
S. scordifolia, S. viscidula[16,23−25] 30 Carthamidin C15H12O6 S. baicalensis [13,20] 31 Carthamidin-7-O-β-D-glucuronide C21H20O12 S. baicalensis [22] 32 Chrysin C15H10O4 S. baicalensis, S. amoena,
S. scordifolia[13,21−24] 33 Chrysin-7-O-β-D-glucuronide C21H20O9 S. baicalensis, S. amoena [23,29] 34 Dihydrobaicalin C21H20O11 S. baicalensis [22,28] 35 Dihydrooroxylin A C21H20O11 S. baicalensis [13] 36 Genkwanin C16H12O5 S. baicalensis [16] 37 Isocarthamidin C15H10O6 S. baicalensis [20,28] 38 Isocarthamidin-7-O-β-D-glucuronide C21H20O12 S. baicalensis [28] 39 Isoschaftside C26H28O14 S. baicalensis [13,16] 40 Isoscutellarein C15H10O6 S. baicalensis [21,30] 41 Isoscutellarein 8-O-β-D-glucuronide C21H18O12 S. baicalensis [21] 42 Kaempferol 3-O-β-D-glucopyranoside C21H20O11 S. baicalensis [13,28] 43 Luteolin C15H10O6 S. baicalensis [22,30] 44 Norwogonin-7-O-glucuronide C21H18O12 S. baicalensis, S. amoena [13,17,23] 45 Oroxylin A C16H12O5 S. baicalensis, S. amoena [17,23] 46 Oroxylin A-7-O-D-glucopyranside C22H22O10 S. baicalensis [22,28] 47 Oroxylin A-7-O-β-D-glucuronide C22H20O11 S. baicalensis, S. amoena [13,23] 48 Pinocembrin C16H12O5 S. baicalensis [13] 49 Pinocembrin-7-O-glucuronide C21H20O11 S. baicalensis [13,16,22] 50 Salvigenin C18H16O6 S. baicalensis [21] 51 Scutellarein C15H10O6 S. baicalensis [28] 52 Scutellarin C21H18O12 S. baicalensis, S. amoena,
S. scordifolia, S. viscidula[23−25,29] 53 Wogonin C16H12O5 S. baicalensis, S. amoena,
S. scordifolia, S. viscidula[21−25] 54 Wogonoside C22H20O11 S. baicalensis, S. viscidula [13,25] In 1976, Takido et al.[20] isolated two flavanone derivatives, carthamidin and isocarthamidin, for the first time as natural products from the leaves of S. baicalensis. Later, Yukinori et al.[21] identified two new flavanones, (2S)-5,7,8,4'-tetrahydroxyflavanone 7-O-β-D-glucuronopyranoside and (2S)-5,6,7,4'-tetrahydroxyflavanone 7-O-β-D-glucuronopyranoside), in the leaves of S. baicalensis. Eight compounds of chrysin, wogonin, apigenin, salvigenin, scutellarein, isoscutellarein, apigenin 7-O-glucuronide, and isoscutellarein 8-O-glucuronide were also isolated. Wang et al.[15] used column chromatography to isolate seven flavonoids (wogonin, chrysin, 5,6,7-trihydroxy-4'-methoxyflavone, carthamindin, isocarthamidin, scutellarein, and chrysin 7-O-β-D-glucuronide) from a water extract of the leaves of S. baicalensis. Liu et al.[13] identified 21 flavonoids in the stems and leaves of S. baicalensis by HPLC-UV/MS and NMR, and found one flavonone (5,6,7,3',4'-Pentahydroxyflavone-7-O-glucuronide) was a new compound. Zhao[17] firstly isolated 5,6,7,4′-tetrahydroxyflavanone 7,5,7-dihydroxy-6-methoxyflavanone, oroxylin A, 5,4′-dihydroxy-6,7,8,3′-tetramethoxyflavone, 5,2′-dihydroxy-6,7,8,3′-tetramethoxyflavone, 5,2′-dihydroxy-7,8,6′-trimethoxyflavone, 5,2′-dihydroxy-7,8-dimethoxyflavone, 5,2′-dihydroxy-6,7,8-trimethoxyflavone, apigenin 4'-β-D-glucopyranoside, and apigenin-7-β-D-glucopyranoside from the aerial parts of S. baicalensis. Ma[22] firstly isolated 5,7,4'-trihydroxy-6-methoxyflavone, 5,4'-dihydroxy-6,7,3',5'-tetramethoxyflavone, from stems and leaves of S. baicalensis. Wang et al.[16] isolated 5,4'-dihydroxy-7-methoxyflavanone, genkwanin, 7-methoxychrysin, 3',4',5,5',7-pentamethoxyflavone from 60% ethanol extracts for stems and leaves of S. baicalensis for the first time. Also, the compounds of carthamidin-7-O-β-D-glucuronide, oroxylin A-7-O-β-D--glucuronide, and chrysin were isolated from this plant for the first time.
The concentration of these chemical components in HQT varies depending on the plant part utilized. Employing the HPLC-DAD method, Shen et al.[18] established that the aerial parts (stems, leaves, and flowers) of S. baicalensis are rich in flavonoids, resembling the roots in composition but exhibiting significant disparities in content. The contents of isocarthamidin-7-O-β-D-glucuronide (106.66 ± 22.68 mg/g), carthamidin-7-O-β-D-glucuronide (19.82 ± 11.17 mg/g), and isoscutellarein-8-O-β-D-glucuronide (3.10 ±1.73 mg/g) were the highest in leaves. The content of apigenin-7-O-β-D-glucopyranoside (18.1 ± 4.85 mg/g) and chrysin-7-O-β-D-glucuronide (9.82 ± 5.51 mg/g) were the highest in flowers. HQT has a high content proportion of flavone glycosides, which is closely related to the activity of HQT. The concentrations of the nine main flavonoids in HQT infusions were measured using HPLC. The content of isocarthamidin-7-O-β-D-glucuronide (52.19 ± 29.81 mg/g) was the highest; carthamidin-7-O-β-D-glucuronide (31.48 ± 6.82 mg/g), chrysin-7-O-β-D-glucuronide (10.65 ± 0.40 mg/g) and apigenin-7-O-β-D-glucopyranside (5.39 ± 0.92 mg/g) were found at moderate levels in HQT samples. As for flavone aglycones, scutellarin (12.77 ± 1.14 mg/g), baicalin (1.88 ± 0.48 mg/g), isoscutellarein-8-O-β-D-glucuronide (2.84 ± 0.60 mg/g), wogonoside (0.23 ± 0.02 mg/g) and chrysin (0.03 ± 0.01 mg/g) has lower content in HQT[6].
Although there are few studies on the chemical constituents of the aerial parts of S. amoena, S. scordifolia, and S. viscidula it has been shown that the compounds of the aerial parts are similar to S. baicalensis. The aerial parts of S. amoena contain the compounds of baicalein, baicalin, oroxylin A, oroxylin A-7-O-β-D-glucuronide, wogonin, chrysin, chrysin-7-O-β-D-glucuronide, norwogonin, 5,7-dihydroxy-6,8-dimethoxyflavone, scutellarin[23]. Zhang et al.[24] identified compounds of chrysin, wogonin, baicalein, apigenin, apigenin-7-O-β-D-glucoside, baicalin, and scutellarin in whole plants of S. scordifolia. The stems and leaves of S. viscidula all contain compounds of wogonoside, apigenin, baicalein, wogonin, baicalin, and scutellarin. The contents of baicalein, wogonoside, wogonin, and apigenin in the stem of S. viscidula were higher than those in the stem of S. baicalensis. In the leaves of the two species, the content of scutellarin was higher, while the content of other compounds was lower[25]. The content of scutellarin in S. viscidula was stem (2.30%) > leaf (1.78%) > flowers (0.38%)[26].
Essential oils
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The aerial parts of S. baicalensis are rich in essential oils, and the taste of HQT is closely related to this. The flowers of S. baicalensis are thought to have a Concord grape aroma, while HQT has a bitter flavor with distinctive herbal notes. Extensive analysis has identified 145 components in the essential oil obtained from the aerial parts of S. baicalensis. These components span various chemical classes, such as alkanes, carboxylic acids, fatty acids, monoterpenes/oxygenated monoterpenes, sesquiterpenes triterpenoids and Vitamins (Supplemental Table S1), which have demonstrated their efficacy in combatting bacteria, reducing inflammation and inhibiting tumor growth[27−31]. Among these, major constituents include germacrene D (5.4%−39.3%), β-caryophyllene (29.0%), caryophyllene (18.9%), eugenol (18.4%), caryophyllene (15.2%), caryophyllene oxide (13.9%), (E)-β-caryophyllene (11.6%), 5-en-3-stigmasterol (11.3%), carvacrol (9.3%), thymol (7.5%), vitamin E (7.4%), neophytadiene (7.3%), γ-elemene (6.2%), 1-octen-3-ol (6.1%), allyl alcohol (5.5%), bicyclogermacrene (4.8%), myristicin (4.7%), acetophenone (4.6%), α-amyrin (4.6%), β-amyrin (4.4%), germacrene d-4-ol (4.3%), spathulenol (4.2%), β-pinene (4.1%), α-humulen (4.0%), 1-vinyl-1-methyl-2-(1-methylvinyl)-4-(1-methylethylidene)-cyclohexane (4.0%) are found in the aerial parts of S. baicalensis from different places[27−31].
Takeoka et al.[27] identified 64 components in volatile components of S. baicalensis flowers by solid-phase microextraction and analyzed them by GC and GC-MS. These flowers were collected at San Francisco State University (USA). Among the flower volatiles, the content of β-caryophyllene, germacrene D, δ-cadinene, γ-muurolene, and γ-cadinene were more than 3%. The essential oil obtained from the stem of S. baicalensis is mainly composed of diphenylamine, 2,2-methylenebis (6-tert-butyl-4-methylphenol), bornyl acetate, β-caryophyllene, germacrene D and 1-octen-3-ol.[32]. Gong et al.[28] analyzed and identified the specific chemical constituents of the aerial parts of S. baicalensis by using GC-MS technology and identified 37 compounds in total, such as allyl alcohol, acetophenone, caryophyllene, α-humulene, germacrene D, and γ-elemene. The plant material was collected in the Qinling Mountains in China. Lu et al.[29] found a big difference in essential oil components between the aerial and root of S. baicalensis from Kunming Botanical Garden, Yunnan Province (China). The aerial part of S. baicalensis mainly contained enols and sterols such as neophytadiene and vitamin E. However, it has the same compounds as the roots, such as nerolidol, hexadecanoic acid, 1,2-benzenedicarboxylic acid, squalene, stigmast-4-en-3-one, and partial alkanes. Recently, Wang et al.[31] found the essential oil level of the aerial parts of S. baicalensis was 0.09% (v/w, based on fresh weight) while its density was 0.93 g/mL, and obtained 31 components accounting for 97.64% of the crude essential oil, including sesquiterpenoid, monoterpenoids, phenylpropanoids, and others. It is also reported that the major components of the essential oil from the aerial parts of S. baicalensis were myristicin, eugenol, caryophyllene, caryophyllene oxide, germacrene D, spathulenol, and β-pinene, with eugenol as the most abundant. The sample of the aerial parts were harvested from Tangshan City (China). The composition of S. baicalensis essential oils varies according to the plant part used, geographical location, and growing conditions.
Others
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Zgórka & Hajnos[33] identified the phenolic acid compounds of aerial parts of S. baicalensis by solid-phase extraction and high-speed countercurrent chromatography: p-coumaric acid, ferulic acid, p-hydroxybenzoic acid, and caffeic acid. Chirikova & Olennikov[34] found that the aerial part of S. baicalensis contains 11 kinds of saturated fatty acids and nine kinds of unsaturated fatty acids, among which the palmitic acid content is the highest. Chlorogenic acid, fernlic acid, protocatechuic acid, vanillic acid, rosmarinic acid, caffeic acid, p-hydroxybenzoic acid, and p-coumaric acid were also detected.
Zhao [17] isolated four sterol compounds: β-sitosterol-3-O-β-D-glucoside, α-apinasterol, β-sitosterol, and four ester compounds: methoxyphaeophorbide, p-hydroxybenethyl ethanol hexadecanoic methyl ester, ethoxyphaeophorbide, and n-octadecanol, lutein from the aerial parts of S. baicalensis.
It is reported that flavonoids and diterpenes are the two main groups of active constituents in the genus Scutellaria. However, only one diterpene (scutebaicalin) was identified in the stems and leaves of S. baicalensis[35].
By atomic absorption spectrophotometry, Yuan et al.[36] determined the contents of 11 metal elements in different parts of S. baicalensis. It was found that the leaves and stems of S. baicalensis were rich in Mg, K, Cr, Ni, Co, Fe, Mn, and Pb. Meanwhile, Yan et al.[37] developed an inductively coupled plasma mass spectrometry method and determined 23 kinds of inorganic elements in the stems and leaves of S. baicalensis from eight regions. Although there were no differences in the types of inorganic elements in the stems and leaves of S. baicalensis from the different areas, the content of these elements varied significantly. Among these elements, Fe, Zn, Cu, Mn, Cr, Co, Ni, Sr, B, and Ni were essential human body elements. The content of Al (516.83 μg/g) and Fe (700.62 μg/g) was the highest, while the content of B (31.54 μg/g), Ti (23.10 μg/g), Mn (65.64 μg/g), Sr (62.27 μg/g), and Ba (89.68 μg/g) was relatively high.
Olennikov et al.[38] studied the water-soluble polysaccharides from the aerial parts of S. baicalensis from Russia and found that the polysaccharides from S. baicalensis gradually accumulated before flowering and progressively decreased after flowering.
Yan et al.[39] found that the stems and leaves of S. baicalensis were rich in amino acids, and there was no difference in the kinds of amino acids among different producing areas, but there was a significant difference in the contents of amino acids. The content of proline, threonine, glutamic acid, lysine, glutamine, and arginine was higher, and the content of methionine, hydroxyproline, and citrulline was low.
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The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
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About this article
Cite this article
Quan Y, Li Z, Meng X, Li P, Wang Y, et al. 2023. A comprehensive review of Huangqin (Scutellaria baicalensis Georgi) tea: chemical composition, functional properties and safety aspects. Beverage Plant Research 3:31 doi: 10.48130/BPR-2023-0031
A comprehensive review of Huangqin (Scutellaria baicalensis Georgi) tea: chemical composition, functional properties and safety aspects
- Received: 22 August 2023
- Revised: 11 October 2023
- Accepted: 13 October 2023
- Published online: 04 December 2023
Abstract: Huangqin tea (HQT), derived from the aerial parts of various Scutellaria species, in particular S. baicalensis Georgi, has a long history of traditional use in China. Its significance has grown in recent years due to its potential anti-aging, colon cancer chemopreventive, and cardiovascular protective properties. Huangqin tea source plants have identified over 295 chemical constituents, including flavonoids, essential oils, phenolic acids, sterols, diterpenes, polysaccharides, and amino acids. Pharmacological research has underscored the diverse beneficial effects of Huangqin tea and flavonoid extracts. These effects encompass anti-inflammatory, antiviral, anti-bacterial, antipyretic, and analgesic properties, along with neuroprotective effects and protection against cardiovascular and cerebrovascular diseases. Safety studies indicate that HQT is generally safe within recommended dosages and historical use. HQT presents multifaceted potential health benefits, though comprehensive research is necessary to ensure its effectiveness and safety in human applications.
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Key words:
- Bioactivity /
- Chemical composition /
- Huangqin tea /
- Safety /
- Scutellaria