Cleaner production of baicalein by novel high-temperature-little-acid hydrolysis of baicalin

ABSTRACT

Baicalein, usually obtained after the removal of 7-O-β-D-glucuronic acid from baicalin, has strong pharmacological activity. In this study, a novel strategy for efficient and eco-friendly preparation of baicalein was established by high-temperature-little-acid hydrolysis of baicalin. The effects of inorganic acids, solvents, solid–liquid ratio, HCl concentration and hydrolysis duration on the yield of baicalein were investigated by one-factor-at-a-time experiment. Then, an orthogonal experiment design was conducted for the optimal hydrolysis conditions, namely, baicalin was boiled in n-BuOH solution containing 0.50% HCl (w/v) at 130°C for 2.0 h with solid–liquid ratio at 1:25 (g/mL). In the 60-fold scale-up experiment, the yield of baicalein was achieved at 83.5% ± 6.3%, and its purity was increased from 74.2% to 98.7% after purification. Compared with reported methods, acid consumption per unit product of the newly developed strategy was approximately 80 times lower than that of conventional acid hydrolysis, and time consumption was substantially reduced. Overall, the novel strategy showed great prospects for a cleaner large-scale production of baicalein, which provides a new alternative desirable for the preparation of natural products with high efficiency and low consumption in the pharmaceutical industry.

GRAPHICAL ABSTRACT

KEYWORDS:

• Baicalein
• baicalin
• acid hydrolysis
• high-temperature-little-acid hydrolysis

1. Introduction

Scutellariae Radix is the dried root of Scutellaria baicalensis Georgi (Fam. Lamiaceae), which is native to China, Russia, Mongolia, North Korea, and Japan and is widely distributed in these regions nowadays [1,2]. It is one of frequently used herbal medicines for treating colds, fever, diarrhea, jaundice, headache, abdominal pain, and drenching, etc. in clinical practices [3]. Scutellariae Radix is well-known for its functions to clear away heat and dampness, as well as purge fire and detoxify, and this herb has been recorded in the prevailing ‘Chinese Pharmacopoeia (2020 edition),’ ‘British Pharmacopoeia (2023 edition),’ ‘European Pharmacopoeia (11.0 edition)' and ‘Japanese Pharmacopoeia (18th edition)' as an essential herbal medicine [1,4–6].

Flavonoids are the main active constituents of S. baicalensis, which have been widely studied in recent decades [7]. In particular, more than thirty flavonol glycosides have been isolated, including baicalin (CAS: 19057-67-1), wogonoside (CAS: 51059-44-0), scutellarin (CAS: 27740-01-8) and oroxylin A-7-O-glucuronide (CAS: 36948-76-2) [2,8,9]. Among them, baicalin has a much higher content than others and possesses various beneficial effects, including anti-inflammatory [10–12], antioxidant [13–15], antibacterial [16], antiviral [17], anticancer [18–20], and antidepressant activities [21].

In 1922, a trace amount of baicalein (CAS: 491-67-8) was isolated from S. baicalensis for the first time [22]. Further research has shown that baicalein has various pharmacological properties, including neuroprotective [23,24], hepatoprotective [25], antiviral [26] and anti-asthmatic [27] effects. According to recent investigations, baicalein could relieve myocardial injury by suppressing harmful changes caused by lipid peroxidation in cardiomyocytes [28]. However, the content of baicalein in S. baicalensis is extremely low, ranging from only 0.04% to 0.28% naturally, and its yield from raw material by direct extraction was very limited [29–31].

Baicalein can be derived from baicalin by the removal of one glucuronic acid after hydrolysis. The conversion to baicalein largely enhanced its lipid solubility and hydrophobicity, which made it easier to cross gastric mucosa [32,33]. It should be noted that baicalin can only be absorbed in the lower part of the intestine after hydrolysis to baicalein, whereas baicalein showed a broader absorption range throughout the gastrointestinal tract [34,35]. Additionally, baicalein exhibited superior pharmacological activities compared with its original glycoside baicalin [36–39]. On the other hand, baicalin is the most abundant flavonol glycoside in S. baicalensis with a content exceeding 9% (w/w) as required by the prevailing China Pharmacopoeia (2020 edition), the European Pharmacopoeia (11.0 edition) and the British Pharmacopoeia (2023 edition), and even not less than 10% (w/w) by the Japanese Pharmacopoeia (18th edition) [1,4–6]. Furthermore, it was well recognized that a complete hydrolysis of baicalin can help greatly increase the yield of baicalein and reduce production costs [29].

Conventional approaches have been studied for the effective conversion of baicalin or other natural products, including thermal cracking, microbial transformation, enzymatic hydrolysis, and acid hydrolysis. For instance, thermal cracking offered a fast reaction rate, however, accurate temperature manipulation was a challenging operation while the reaction was taking place in a muffle furnace. Consequently, poor experimental reproducibility and large experimental errors have been caused and difficulties in industrialization were to be resolved [40]. Microbial transformation, despite its relatively high specificity and eco-friendliness, usually requires a large time consumption, typically ranging from 5 to 8 days [41,42]. Meanwhile, the purification step of the desired product is always complicated and tedious. Enzymatic hydrolysis, known for its mild reaction conditions and high product quality, suffers from slow reaction rates and relatively high production costs, which much hindered its industrial-scale implementation [43–48]. In addition, conventional acid hydrolysis adopted an aqueous solution of an inorganic acid as the solvent, and a high acid concentration was usually required due to the low boiling point (ca. 100°C) of the reaction system. As a result, significant environmental pollution could be caused unless the acidic liquid waste has been carefully handled [49]. Moreover, strong acids substantially degraded the chemical structure of baicalin, often leading to a low yield [40, 50].

To address these challenges, a novel acidic hydrolysis system has been proposed in the current study. The novelty lies in that an organic solvent of high boiling point was used as the solvent instead of water to increase reaction temperature and consequently only a little of inorganic acid was needed as the catalyst. This approach aimed to reduce the consumption of acids in large-scale production processes and achieve efficient conversion, paving a sustainable way to obtain bioactive flavonoid aglycones with high efficiency and low consumption in the pharmaceutical industry.

2. Materials and methods

2.1. Materials and reagents

Baicalin (purity was 92.0% by HPLC-UV, B/N: 21050603) was offered by Chengdu Pufei De Biotech Co., Ltd. (Chengdu, China). Baicalein (purity ≥ 98.9% by HPLC-UV, B/N: C06M11Y112461) was purchased from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). HPLC-grade methanol (MeOH, B/N: 220151019M08) was obtained from OmniGene LLC (United States). n-Butanol (n-BuOH, B/N: F2130089) of analytical grade was supplied by Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Hydrochloric acid (HCl, B/N: 20160719), sulfuric acid (H₂SO₄, B/N: 20180223), 1-pentanol (B/N: 20220607), ethanol absolute (EtOH, B/N: 20220414) and phosphoric acid (H₃PO₄, B/N: 20130503) were of analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Two macroporous resins D101 and DM130 were bought from Sunresin New Materials Co., Ltd. (Xi’an, China). Ultrapure water (>18.2 MΩ·cm⁻¹) was prepared using a HealForce water purification system (China).

2.2. HPLC conditions

An Agilent 1100 HPLC chromatograph equipped with G1313A autosampler, G1312A pump, G1316A column oven, G1315A diode array detector, and G1322A degasser was used for chromatographic analysis. Data acquisition and post-run processing were performed using HP ChemStation software (Rev.A.07.01[682]). The HPLC analysis was conducted according to the reported conditions with minor modifications [51].

A Waters SunFire C18 column (150 mm L. × 4.6 mm I.D., 5 μm) was used for separation of analytes in HPLC analysis. The injection volume was 5 μL, and the flow rate was set at 1.0 mL/min constantly. Column temperature was maintained at 35°C throughout the analysis, and UV wavelength at 280 nm was employed to monitor HPLC profile. Mobile phases consisted of MeOH (A) and 0.10% H₃PO₄ aqueous solution (B). Gradient elution program was as follows: 0 min, 57%A: 43%B → 10 min, 57%A: 43%B → 13 min, 70%A: 30%B → 23 min, 90%A: 10%B → 25 min, 90%A: 10% B→ 27 min, 57%A: 43%B → 30 min, 57%A: 43%B.

2.3. Preparation of standard solution

Twenty milligrams of baicalein reference were dissolved in MeOH to be 10 mL, then a stock solution with a concentration of 2.000 mg/mL was prepared. Subsequently, a series of dilutions were performed to obtain standard solutions with concentrations of 3.906 × 10⁻³, 7.812 × 10⁻³, 1.562 × 10⁻², 3.125 × 10⁻², 6.250 × 10⁻², 1.250 × 10⁻¹, 2.500 × 10⁻¹, 5.000 × 10⁻¹, and 1.000 mg/mL.

2.4. Preparation of sample solutions by high-temperature-little-acid hydrolysis

To prepare the sample solutions, 4 g of baicalin was accurately weighed and transferred in a round-bottomed flask. Then, 100 mL of acidic n-BuOH solution containing 0.50% HCl (w/v) was added. A heating bowl was heated to 130°C, and then a gentle boiling of the reaction system was observed. After being refluxed for 2.0 h, the system was cooled to ambient temperature. Prior to injection for HPLC analysis, a small portion of the resulting solution was filtered through a 0.22 μm syringe membrane. Determination of baicalein was conducted according to the method described as aforementioned.

2.5. Condition optimization for baicalein preparation

2.5.1. One-factor-at-a-time experiment

One-factor-at-a-time (OFAT) experiment was employed, in which the effects of five variables were investigated, namely inorganic acid (HCl or H₂SO₄), solvent (n-BuOH, 1-pentanol, pure water), solid–liquid ratio (1:50, 1:25, 1:16, 1:12, 1:10, 1:8, g/mL), HCl concentration (0.10%, 0.50%, 1.00%, 3.00%, w/v), and hydrolysis duration (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, h). Each experiment was performed in triplicate, and the yield of baicalein and its average were calculated. The results from the OFAT experiments were used for the subsequent orthogonal design.

2.5.2. Orthogonal experimental design

Based on the results of OFAT experiments, three factors, namely solid–liquid ratio, HCl concentration and hydrolysis duration, were selected to design a four-factor, three-level L₉(3⁴) orthogonal experiment (Table 1) to further optimize and investigate the significance of these factors on the yield of baicalein by means of range analysis and analysis of variance (ANOVA) through IBM® SPSS statistical software (version 23, IBM SPSS, Armonk, NY, U.S.A.).

Table 1. Factors and levels of L₉(3⁴) orthogonal experiment design.

Level	Factors
	Solid–liquid ratio (g/mL)	HCl concentration (%, w/v)	Hydrolysis duration (h)
1	1:25	0.10	1.5
2	1:16	0.50	2.0
3	1:12	1.00	2.5

2.6. Scale-up experiments

To further investigate the applicability of this newly developed technique in the pharmaceutical industry, a scale-up experiment was further performed for a 60-fold increase in the reaction volume from 100 mL to 6 L.

In the scale-up experiments, 240 g of baicalin was accurately weighed in round-bottom flasks, and 6 L of n-BuOH solution containing 0.50% HCl (w/v) was added and mixed. The mixture was heated to 130°C to a slight boiling state and then refluxed for 2.0 h. After cooling to room temperature, n-BuOH in the reaction solution was recycled under reduced pressure at 50°C. After suction filtration on filter paper, crude baicalein was washed with distilled water and then dried at 50°C for 20 h.

2.7. Purification of baicalein

Fifty grams of crude baicalein were dissolved in 30% EtOH (v/v). 150 mL of the sample solution was then loaded onto a glass column packed with DM130 resin. Gradient elution was performed using 30%, 40%, 60%, and 80% EtOH (v/v) (4 BV for each). Its effluent was concentrated and loaded onto another column filled with D101 resin. Elution was performed using 70% EtOH (v/v) at a constant flow rate (2 mL/min). The collected effluent was analyzed by HPLC-UV, and the fractions containing baicalein was lyophilized.

2.8. Identification of baicalein

The purified product was subjected to ESI ⁺-MS, ¹H-NMR, and ¹³C-NMR for structure identification. The NMR analysis was conducted on a Bruker Advance II 400 MHz spectrometer. The solution of the product was injected into a Shim-pack UFLC SHIMADZU CBM30A system in tandem with ESI-QQQ detector for MS data acquisition.

2.9. Calculations

The baicalein concentration (C, mg/mL) of the sample solution was calculated using the calibration curve based on its peak area. The yield of baicalein (Y, %) was calculated using the following equations: (1) $Y\text{\%}={\displaystyle \frac{C\times V\times D\times M}{m\times \omega \times M\times 1000}\times 100}$(1) In the equations, V represents the volume of the reaction system in mL, D represents the dilution factor of sample solution, m represents the mass of baicalin added in acid hydrolysis in grams, ω represents the purity of baicalin (92.0%), M represents the molar mass of baicalein (M: 270.237 g/mol), and M" represents the molar mass of baicalin (M": 446.361 g/mol).

3. Results and discussion

3.1. One-factor-at-a-time experiment

3.1.1. Inorganic acid

The solid–liquid ratio of baicalin to n-BuOH in the reaction system was 1:25 (g/mL), with an acid concentration of 0.50% (w/v) and a hydrolysis duration of 2.0 h. The effect of inorganic acid (HCl or H₂SO₄) on the yield of baicalein was investigated. As shown in Figure 1(a), the yield of baicalein was negligible when no acid was added to the reaction with n-BuOH, which confirms the necessity of acid usage during hydrolysis. The average yield of baicalein using HCl and H₂SO₄ as catalysts was 70.4% ± 3.3% and 62.0% ± 1.0%, respectively. The yield of baicalein with HCl as a catalyst was significantly higher than that of baicalein with H₂SO₄ as a catalyst (13.5%; P < 0.05). Therefore, HCl was selected as the catalyst to construct the novel high-temperature-low-acid hydrolysis system. In this reaction system, HCl provided an acidic environment, the 7-position glycosidic bond atom of baicalin was protonated, and the glycosidic bond was broken to form the aglycone baicalein and the cationic carbon ion intermediate of glucuronic acid, which was solvated in the solvent n-BuOH and then removes hydrogen ions to form glucuronic acid [52,53].

Figure 1. Effects of five parameters on the yield of baicalein. (a) inorganic acid; (b) solvent; (c) solid–liquid ratio; (d) HCl concentration; and (e) hydrolysis duration. Different letters indicate significant differences (p < 0.05), the yield of baicalein was presented as M ± SD (n = 3).

3.1.2. Solvent

n-BuOH or 1-pentanol containing HCl was used as the reaction solvent to reach a higher temperature than acidic aqueous solution, and the yield of baicalein was investigated and compared. As shown in Figure 1(b), the yield of baicalein was only 1.5% ± 0.4% when pure water was used as the solvent with a low HCl concentration at 0.50%. Instead, when n-BuOH and 1-pentanol were used as reaction solvents, the average yield of baicalein was greatly increased to 67.8% ± 1.6% and 74.0% ± 6.5%, respectively. As the boiling point of n-BuOH (ca. 118°C) and 1-pentanol (ca. 137°C) is much higher than that of water, the reaction system composed of either one achieved a greater temperature, which largely promoted the hydrolysis of baicalin. Although the yield of baicalein was slightly higher when 1-pentanol was used as the reaction solvent other than n-BuOH, there was no significant difference between them (P > 0.05). Given the economical aspect, n-BuOH is more cost-effective than 1-pentanol as a reaction solvent.

3.1.3. Solid–liquid ratio

To optimize the solid–liquid ratio, various amounts of baicalin were mixed with 100 mL of acidic n-BuOH solution for hydrolysis and the results are shown in Figure 1(c). When the solid–liquid ratio of baicalin to n-BuOH was changed from 1:50 to 1:25 or 1:16 (g/mL), the yield of baicalein slightly varied around 60% without significance (P > 0.05). A sufficient n-BuOH solution could have made the substrate baicalin dissolved fully, which ensured its complete and efficient hydrolysis. When the solid–liquid ratio was further reduced to 1:12 (g/mL) or less, the yield of baicalein tended to dramatically decline to 34.1% ± 4.0% at 1:8 (g/mL). Due to the limited solubility of baicalin in the reaction system, a large amount of baicalin could not be dissolved in the solvent even if the temperature had reached a high level, which prevented the hydrolysis from accomplishment. Hence, to save the amount of n-BuOH and increase the efficiency of the reaction, the solid–liquid ratio of 1:16 was selected in the optimal hydrolysis conditions.

3.1.4. HCl concentration

When the ratio of baicalin to n-BuOH was 1:16 (g/mL) and the hydrolysis duration was 2.0 h, the effect of HCl concentration on the yield of baicalein was investigated and the results were shown in Figure 1(d). With the increase of HCl concentration from 0.10% to 0.50%, the yield of baicalein increased significantly (P < 0.01) to the point where insufficient acid did not result in a desired full hydrolysis. However, when HCl concentration was further increased to 3.00%, the yield has been decreased to 45.5% ± 5.4%. The resulting baicalein could be extensively converted to byproducts due to the presence of excess acid in the reaction system. The yield of baicalein was the highest (P < 0.05) when the HCl concentration was 0.50%, which was then chosen for subsequent hydrolysis.

3.1.5. Hydrolysis duration

The acid hydrolysis was then performed under the optimum conditions defined above for various durations. As shown in Figure 1(e), the yield of baicalein increased rapidly from 32.5% ± 4.3% to 76.5% ± 7.7% as the hydrolysis lasted from 0.5 h to 2.5 h (P < 0.01). The highest yield of baicalein was obtained at a hydrolysis duration of 2.5 h, indicating the best performance in the conversion of baicalin to baicalein which was required to consume sufficient time. However, the yield was decreased moderately when an additional half an hour was spent to hydrolyze the substrate baicalin (P > 0.05). This could be because 0.50% HCl (w/v) was completely consumed within 2.0 h, which negatively affected baicalein production.

3.2. Orthogonal experimental design

The results of the L₉(3)⁴ orthogonal experiment were presented in Table 2, and range analysis was performed using the yield of baicalein as the index. The R-values of the three factors, namely solid–liquid ratio (A), HCl concentration (B), and hydrolysis duration (C), indicated that the influence on the yield of baicalein followed the order of B > A > C. The results of variance analysis, as presented in Table 3, revealed that all three factors had a significant impact on the yield of baicalein. The best conditions for high-temperature-little-acid hydrolysis were determined to be B₂A₁C₂, which corresponded to a solid–liquid ratio of 1:25, HCl concentration of 0.50%, and hydrolysis duration of 2.0 h.

Table 2. Results and analysis of L₉(3)⁴ orthogonal experiment.

No.	A (g/mL)	B (%, w/v)	C (h)	D (blank)	Yield (%)
1	1:25	0.10	1.5	1	35.3
2	1:25	0.50	2.5	2	70.3
3	1:25	1.00	2.0	3	62.6
4	1:16	0.10	2.5	3	37.9
5	1:16	0.50	2.0	1	63.9
6	1:16	1.00	1.5	2	40.4
7	1:12	0.10	2.0	2	33.3
8	1:12	0.50	1.5	3	44.3
9	1:12	1.00	2.5	1	49.7
K1	1.682	1.065	1.200	1.489
K2	1.423	1.785	1.598	1.440
K3	1.272	1.527	1.579	1.448
k1	0.561	0.355	0.400	0.496
k2	0.474	0.595	0.533	0.480
k3	0.424	0.509	0.526	0.483
R	0.137	0.240	0.133	0.016

Note: R refers to the result of extreme difference.

Table 3. Variance analysis of L₉(3)⁴ orthogonal experiment.

Factors	SS	df	MS	F	P	Significant
Model	0.151^a	6	0.02514	108.556	0.0092	**
Intercept	2.129	1	2.129	9189.69	0.0001	**
Solid–liquid ratio (A)	0.02871	2	0.01435	61.9609	0.0159	*
HCl concentration (B)	0.08864	2	0.04432	191.328	0.0052	**
hydrolysis duration (C)	0.03353	2	0.01677	72.3785	0.0136	*
Blank (D)	0.00046	2	0.00023
Total	2.280	9
Cor total	0.15134	8

*Significant (p < 0.05).

**Extremely significant (p < 0.01).

^a R-squared = 0.997 (adjusted R-squared = 0.988).

3.3. Scale-up experiment

The hydrolysis efficiency of high-temperature-little-acid hydrolysis of baicalin was further investigated in a sixty-time scale-up experiment. The results demonstrated that after a 2-h hydrolysis of baicalin, a crude product of baicalein was obtained by the newly proposed approach, and complete hydrolysis of the substrate was observed in a typical HPLC chromatogram (Figure S2). The purity of baicalein in the crude product was determined to be 74.2%, and the yield of baicalein was calculated to be 83.5% ± 6.3%.

3.4. Purification of baicalein

In the subsequent purification of baicalein from a crude product, DM130 and D101 macroporous resins were utilized in sequence according to the routine procedure. As a result, the purity of baicalein was increased from 74.2% to 98.7%, and the resulting product was exhibited as yellow powder (Figure 2). The improved product purity was attributed to the removal of the by-product (glucuronic acid) as well as other impurities caused by butyl esterification of baicalin and additional reaction between baicalein, glucuronic acid and n-BuOH.

Figure 2. Crude baicalein and purified baicalein by macroporous resins. (A) Crude baicalein; (B) baicalein purified by DM130 macroporous resin; (C) baicalein purified by DM130 and D101 macroporous resins.

3.5. Identification of baicalein

After sequential purification by two types of macroporous resin, the fraction containing baicalein was collected and pooled. Its purity was determined to be ≥ 98% by HPLC-UV analysis. Furthermore, to confirm the chemical structure of the resulting baicalein, spectrometric techniques including LC-ESI ⁺-MS, ¹H-NMR, and ¹³C-NMR were employed (Figure S3).

LC-ESI ⁺-MS: m/z 271.10 [M + H]⁺, 269.10 [M-H]; ¹H-NMR (400 MHz, DMSO-d₆) δ: 12.66 (1H, s, 5-OH), 10.58 (1H, s, 7-OH), 8.82 (1H, s, 6-OH), 8.06 (2H, dd, J = 8.0, 1.5 Hz, H-1′, 6′), 7.68–7.45 (3H, m, H-3′, 4′, 5′), 6.93 (1H, s, H-3), 6.63 (1H, s, H-8); ¹³C-NMR (100 MHz, DMSO-d₆) δ: 182.40 (CO), 163.18 (C-2), 153.91 (C-7), 150.11 (C-9), 147.25 (C-5), 132.10 (C-4′), 131.25 (C-1′), 129.60 (C-6), 129.39 (C-3′), 126.58 (C-2′), 104.76 (C-3), 104.56 (C-10), 94.29 (C-8). The above data were consistent with references [54–56], and accordingly the compound was identified as baicalein.

3.6. Comparison between the novel strategy and reported methods

To validate the applicability of the new strategy proposed in this study, it was compared with reported methods for the preparation of baicalein from baicalin. The results of the comparison are summarized in Table 4. Compared with the conventional acid hydrolysis, the yield of baicalein by the newly proposed strategy was 83.5% ± 6.3%, and the amount of acid consumed per gram of baicalein was only 0.6683 mL, which was approximately 80 times lower than that of the conventional acid hydrolysis [50]. In addition, a complete conversion of baicalin was not achieved even after 20-h enzymatic hydrolysis or 7-d fermentation [57,58], whereas the conversion rate of the new method reached 100% in 2.0 h. Therefore, the method newly developed in this study was much more efficient and environmentally friendly. In recent decades, many comprehensive utilization approach of natural resources have been developed to reduce environmental pollution and make value-added products, meeting the principles of green chemistry [59–61]. In future studies, efforts could be put into the recovery of free glucuronic acid released from high-temperature-little-acid hydrolysis of baicalin.

Table 4. Verification experiments and comparison with other methods.

Methods	Hydrolysis duration	Acid consumption/1 g baicalein	Conversion rate of baicalin	Yield of baicalein	References
Conventional acid hydrolysis	1.5 h	54.00 mL	–	89.9% ± 4.38%	[50]
Enzymatic hydrolysis	20∼24 h	–	88.4%	–	[57]
Fermentation	7 d	–	96.5%	–	[58]
Newly proposed strategy	2.0 h	0.6683 mL	100%	83.5% ± 6.3%	This work

4. Conclusion

In this study, high-temperature-little-acid hydrolysis of baicalin has been proposed to minimize acid usage for efficient preparation of baicalein. The reaction system was composed of n-BuOH instead of water to achieve a high temperature and only a little HCl was added as catalyst. The reaction time of the newly developed strategy was significantly shorter than enzymatic hydrolysis and fermentation. In addition, the acid consumption per gram of baicalein was approximately 80-fold reduction in comparison with conventional acid hydrolysis. The novel strategy established in this study can reduce the amount of acid and complete the conversion reaction in a short time, which is very suitable for the large-scale preparation of natural active ingredients in the pharmaceutical industry.

Acknowledgements

Lingling Tang: Investigation, Validation, Writing – Original draft preparation. Jiali Shao: Methodology, Visualization. Hanxue Zheng: Investigation, Formal analysis. Jixuan Chen: Data Curation. Guohua Xia: Resources, Funding acquisition. Huan Yang: Supervision, Resources. Yaya Yang: Project administration, Writing – Review & Editing. Yuping Shen: Conceptualization, Supervision, Writing – Review & Editing, Funding acquisition. All the authors gave their final approval for publication.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [grant number 81873196], and the Science and Technology Project of Changzhou City [grant number CJ20220161].