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Antioxidant and alpha-glucosidase inhibitory activities of flavonoids isolated from fermented leaves of Camellia chrysantha (Hu) Tuyama

  • Thi Nhu Hang Tran ORCID logo , Thi Tuyen Tran ORCID logo , Bach Cao Pham ORCID logo , Kim Chi Hoang ORCID logo , Tien Quan Nguyen ORCID logo , Anh Vien Trinh ORCID logo and Van Thi Hong Nguyen ORCID logo EMAIL logo
Published/Copyright: May 23, 2025
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Turkish Journal of Biochemistry
From the journal Turkish Journal of Biochemistry Volume 50 Issue 3

Abstract

Objectives

Microbial fermentation has long been known as a method for processing teas to raise products with novel biological activities. Our study aimed to chemically characterize flavonoid components in fungal mediated biotransformed Camellia chrysantha (Hu) Tuyama leaves.

Methods

The fermented leaves of Camellia chrysantha were prepared by inoculation with an Eurotium cristatum fungal consortium and extracted with ethanol combining ultrasound-assisted technique, before introducing to chemical characterization. Normal and reverse phase C18 column chromatography and thin layer chromatography were applied for fractionation and isolation of compounds from the ethanolic extract. Nuclear magnetic resonance spectra (1H NMR, 13C NMR, HSQC and HMBC) were recorded for structure determination, while in vitro bioassays of free radical scavenging capacity and α-glucosidase inhibition were employed to assess anti-oxidative and anti-diabetic properties of isolated compounds.

Results

Four flavonoids, i.e. quercitrin (1), afzelin (2), (-)-epicatechin (3), and engelitin (4) were isolated from fermented Camellia chrysantha (Hu) Tuyama leaves. Compounds 1 and 3 were found to exhibit scavenging property against both DPPH and ABTS. Compound 2 was noticeably the most effective against α-glucosidase, presenting an IC50 of 78.25 μg/mL.

Conclusions

The investigation on chemical composition of microbial fermented leaves of Camellia chrysantha (Hu) Tuyama brought out flavonoid compounds with significant biological activities, which could serve as a basis for further possible application in manufacturing health protecting natural products.

Keywords: Camellia chrysantha ; fermented leaves; flavonoids; antioxidant; α-glucosidase

Introduction

Camellia chrysantha (Hu) Tuyama (Theaceae), popularly named as “golden camellia”, is an evergreen shrub with predominant distribution in wet forest areas of Vietnam and southern China [1]. The camellia has not only been well known as a valuable ornamental plant but also been acknowledged as a beneficial herbal tea for relieving symptoms of diabetes mellitus, hyperlipidemia and atherosclerosis, as well as controlling blood pressure and cardiovascular disorders [1]. Previous phytochemical investigation emphasized flavonoids as the most antioxidant active components in C. chrysantha leaves [2].

Microbial fermentation is among the most common methods of food preservation and post-harvest treatment. During the process, biochemical transformations occurred and altered the chemical composition, bioactivities and digestibility of the original materials [3]. Notably, the biotransformation may induce structural breakdown of plant cell walls, leading to the liberation and/or the synthesis of antioxidants in the final products [4]. On the other hand, its enhanced antioxidant property was found to be proportional to the increased level of phenolic and flavonoid compounds resulting from microbial hydrolysis reactions [4]. Regarding the importance in defending our bodies against oxidative damage, the alleviation of antioxidants by manufacturing herbal leaves using microbial fermentation may support health with multiple benefits.

In recent years, the dramatical increase of type 2 diabetes mellitus has become a serious medical concern worldwide. One of the most effective treatments against the disorder is to retard the absorption of digestive glucose by inhibiting carbohydrate hydrolyzing enzymes, most importantly α-glucosidase and α-amylase. Typical α-glucosidase inhibitors, i.e. acarbose and voglibose, were reported to associate with side effects, including gastrointestinal disease and kidney issues [5]. Therefore, the need for isolating novel and effective α-glucosidase inhibitors remains enormous. Flavonoids and phenolic compounds from plants as well as their fermented products could be considered the most significant and abundant sources for the exploiting purpose.

The present study focused on the bioactivity guided phytochemical investigation of microbial fermented Camellia chrysantha leaves. Additionally, the effects of the fungal fermentation on tea leaves were aimed to be considered.

Materials and methods

General

The nuclear magnetic resonance (NMR) spectra of compounds were recorded using a Bruker AM600 FT – NMR (1H NMR (CD3OD, 600 MHz) and 13C NMR (CD3OD, 150 MHz)) at the Institute of Chemistry, Vietnam Academy of Science and Technology (VAST). Column chromatography (CC) was performed on normal phase silica gel (60–230 mesh and 230–400 mesh, Merck) or reverse phase C18 (30–50 μm, Merck). Thin layer chromatography (TLC) was conducted on pre-coated silica gel DC-Alufolien 60 F254 (Merck), utilizing an ultraviolet lamp (UV) at 254 and 365 nm, along with a 10 % aqueous H2SO4 solution and heating.

Reagents [(2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis(3-etilbenzotiazolin)-6-sulfonic acid (ABTS))], standards (ascorbic acid, acarbose), enzyme (α-glucosidase from Saccharomyces cerevisiae) and substrate [4-nitrophenyl α-d-glucopyranoside (pNPG)] were purchased from Sigma-Aldrich Co. (St Louis, MO, USA). Methanol, dimethylsufoxide (DMSO) with a purity of over 98 % were purchased from Xilong Scientific Co., Ltd (Guangdong, China).

Plant materials

Fresh leaves of Camellia chrysantha were collected at cultivation area in Bache, Quangninh, Vietnam (21°19′34.2″N 107°06′07.7″E) in May 2022. After plucking, they were washed and spread outdoor to reduce the moisture level. Then, the tea leaves were steamed at 121 °C for 20 min to inactivate endogenous enzymes [polyphenoloxidase (PPO) and peroxidase (POD)].

Followingly, the tea leaves underwent microbial fermentation by inoculating with Eurotium cristatum fungal spores. In detail, 10 mL of fungal suspension (5 × 106 CFU/mL) was added to 100 g of primarily processed leaves, stirred and then incubated in whole (21 days, 25 °C, protected from light).

Extraction and isolation

The fermented leaves of Camellia chrysantha (Hu) Tuyama (3 kg) were extracted with ethanol three times (each 10 L, 2 days) at 50 °C combining a conventional ultrasound-assisted technique, and then the solvent was removed by evaporation in vacuo to yield the total ethanol extract (600 g). The ethanolic extract residue was suspended in water (2.0 L) and successively partitioned with n-hexane and ethyl acetate to yield n-hexane (THV-LM/H, 120 g) and ethyl acetate (THV-LM/E, 250 g) extracts. THV-LM/E was chromatographed on a normal phase silica gel column, eluted with dichloromethane:methanol:water gradient system (4:1:0.05 to 0:100:0, v:v:v) to give three fractions, THV-LM/E1, THV-LM/E2, and THV-LM/E3. The THV-LM/E1 fraction was chromatographed on a normal phase silica gel column, eluted with the gradient solvents of dichloromethane:methanol:water (10:1:0.05, v:v:v) to yield three fractions, THV-LM/E1.1 - THV-LM/E1.3. The TH-LM/E1.2 fraction was chromatographed on a RP-18 column eluting with methanol:water (3:1, v:v) to yield compounds 2 (10 mg), 3 (8 mg) and 4 (7 mg). Compound 1 (10 mg) was obtained from THV-LM/E1.3 fraction using a PR-18 column and eluting with methanol:water (1:1, v:v).

Quercitrin (1): Yellow amorphous powder, 1H NMR (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD); see Table SV-1 and Table SV-2. MW: 448.30, Formula: C20H18O6

Afzelin (2): Yellow amorphous powder, 1H NMR (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD); see Table SV-1 and Table SV-2. MW: 432.38, Formula: C21H20O10 .

(-)-Epicatechin (3): Yellow amorphous powder, 1H NMR (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD); see Table SV-1 and Table SV-2. MW: 290.27, Formula: C15H14O6

Engelitin (4): White amorphous powder, 1H NMR (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD); see Table SV-1 and Table SV-2. MW: 434.39. Formula: C21H22O10

Assessment of biological activites

Antioxidant assays

The antioxidant property of test substances isolated from fermented leaves of Camellia chrysantha was evaluated by scavenging capacity against both DPPH and ABTS free radicals.

In the DPPH radical scavenging assay, 10 μL of dissolved test sample in DMSO was mixed with 190 μL DPPH solution and incubated in the dark for reaction (37 °C, 30 min). The scavenging capacities (SC) of samples were determined by comparison of test samples’ absorbance values with the control value obtained at the wavelength of 515 nm by microplate reader (Tecan F150, Austria) [6], 7].

The ABTS radical cation decolorization assay was performed in 96-well plates as reported by Re et al. (1999). For preparation of ABTS+ radical solution, dissolved ABTS in H2O (7 mM) was mixed with 2.45 mM potassium persulfate (room temperature, 16 h, protected from the light). Subsequently, a reaction mixture of dissolved extract in DMSO (10 μL) and 190 μL of ABTS+ radical solution was composed and incubated in the dark (37 °C, 30 min). The quantification of scavenged blue–green radical cation was monitored spectrophotometrically at 734 nm.

In both assays, DMSO served as the negative control, while ascorbic acid was applied as the positive control. SC50 values of antioxidative test samples were calculated by interpolation from linear regression analysis.

Alpha-glucosidase inhibitory assay

The α-glucosidase inhibitory potential of the test samples was assessed by a method of Tadera et al. on 96-well microplates with minor modifications [8]. In brief, a reaction mixture containing 91.75 μL phosphate buffer (100 mM, pH=6.8), 0.75 μL α-glucosidase (20 U/mL), and 7.5 μL of varying concentrations of crude extracts was preincubated at 37 °C for 15 min. Then, 50 μL of substrate p-NPG (1 mM) was added and further incubated (37 °C, 20 min). The reaction was stopped by adding 50 μL Na2CO3 (0.1 M). The absorbance of the released p-nitrophenol was measured at 405 nm (Tecan F150, Austria). Acarbose was used as a standard. Results were presented as percentages of inhibition, which were calculated using the following formula:

Inhibition  % = 100 × A + − A − − A 1 − A 0 / A + – A −

In this formula, A+ denotes the absorbance of the positive control (Acarbose), A- refers to the absorbance of the negative control, A1 represents the absorbance of the test sample, and A0 is the blank absorbance.

IC50 values of the test samples exhibiting inhibiting potential inhibition were estimated through interpolation from linear regression analysis.

Results

Biological activities of fermented leaves extracts

The n-hexane (THV-LM/H) and ethyl acetate (THV-LM/E) extracts were tested for their antioxidant (Table 1) and α-glucosidase inhibition activities (Table 2). The obtained results indicated more potent free radical scavenging effects of the ethyl acetate extract, while the n-hexane counterpart exhibited more significant inhibition against α-glucosidase. With regard to the antioxidative property, THV-LM/E showed SC50 values of 121.39 ± 0.57 and 45.72 ± 0.28 μg/mL against DPPH and ABTS, respectively, and the ethyl acetate extract was chosen for further study on its chemical constituents.

Table 1:

Scavenging capacities against DPPH and ABTS of fermented leaves extracts.

No Sample Sample conc., μg/mL DPPH assay ABTS assay
SC, % SC50, μg/mL SC, % SC50, μg/mL
1 THV-LM/H 400 47.68 ± 0.41 – 79.25 ± 0.18 273.26 ± 0.23
200 – 35.09 ± 0.25
100 – 12.47 ± 0.27
2 THV-LM/E 400 81.81 ± 0.62 121.39 ± 0.57 90.14 ± 0.27 45.72 ± 0.28
200 73.07 ± 0.48 86.12 ± 0.23
100 42.51 ± 0.41 80.97 ± 0.18
Ascorbic acid 50 87.48 ± 0.38 9.75 ± 0.22 92.18 ± 0.28 7.82 ± 0.11
Table 2:

α-glucosidase inhibitory activities of fermented leaves extracts.

No Sample Sample conc., μg/mL α-glucosidase inhibition
Inhibition, % IC50, μg/mL
1 THV-LM/H 400 84.24 ± 0.35 24.32 ± 0.31
200 80.35 ± 0.28
100 77.62 ± 0.29
2 THV-LM/E 400 78.03 ± 0.72 66.21 ± 0.66
200 75.35 ± 0.6
100 66.43 ± 0.46
Acarbose 50 81.42 ± 0.31 11.61 ± 0.43

Biological activities of fractions

Three fractions (THV-LM/E1→THV-LM/E3) obtained from the ethyl acetate extract was evaluated for their antioxidative and α-glucosidase inhibitory properties. As shown in Table 3, the free radical scavenging capacity of THV-LM/E1 fraction was at a peak with SC50 values of 103.26 ± 0.35 and 25.58 ± 0.15 μg/mL against DPPH and ABTS, respectively.

Table 3:

Antioxidative activity of fractions obtained from the ethyl acetate extract of fermented leaves.

No Sample Sample conc., μg/mL DPPH assay ABTS assay
SC, % SC50, μg/mL SC, % SC50, μg/mL
1 THV-LM/E1 400 75.52 ± 0.42 103.26 ± 0.35 92.12 ± 0.26 25.58 ± 0.15
200 66.35 ± 0.42 87.53 ± 0.31
100 48.13 ± 0.42 79.12 ± 0.22
2 THV-LM/E2 400 77.01 ± 0.6 155.15 ± 0.31 92.28 ± 0.17 43.73 ± 0.23
200 59.14 ± 0.42 81.91 ± 0.25
100 38.52 ± 0.42 69.96 ± 0.16
3 THV-LM/E3 400 41.83 ± 0.91 – 89.94 ± 0.28 131.98 ± 0.11
200 – 72.51 ± 0.22
100 – 37.07 ± 0.15
Ascorbic acid 50 86.72 ± 0.22 10.17 ± 0.24 91.73 ± 0.21 8.14 ± 0.14

Among three fractions, THV-LM/E1 appeared as the most potent α-glucosidase inhibitor with IC50 value of 12.84 ± 0.51 μg/mL (Table 4). In accordance with its antioxidant property (Table 3), this fraction was thus chosen for isolation of pure compounds. The combination of CC and TLC methods led to the isolation of four compounds 1–4 from THV-LM/E1 fraction.

Table 4:

α-glucosidase inhibitory activity of fractions obtained from the ethyl acetate extract of fermented leaves.

No Sample Sample conc., μg/mL α-glucosidase inhibition
Inhibition, % IC50, μg/mL
1 THV-LM/E1 400 91.65 ± 0.21 12.84 ± 0.51
200 88.42 ± 0.38
100 80.16 ± 0.33
2 THV-LM/E2 400 83.16 ± 0.35 36.13 ± 0.48
200 79.28 ± 0.41
100 70.75 ± 0.33
3 THV-LM/E3 400 27.38 ± 0.33 –
200 –
100 –
Acarbose 50 83.02 ± 0.47 10.47 ± 0.73

Isolation and identification of pure compounds

Four compounds (1–4, Figure 1) have been isolated from the most active fraction of the microbial fermented Camellia chrysantha leaves’ ethyl acetate extract. Their chemical structures were elucidated by analysis of 1D and 2D NMR spectroscopy and by comparison with reported data (Table SV-1 and Table SV-2).

Figure 1: The chemical structures of compounds 1–4.
Figure 1:

The chemical structures of compounds 1–4.

Compound 1 was a yellow amorphous powder. The NMR spectra of 1 presented the signals of a flavonoid glycoside, including one rhamnopyranosyl moiety. In comparing the 1H NMR, 13C NMR, HSQC and HMBC spectral data of 1 with those reported [9], compound 1 was identified as quercitrin (quercetin 3-O-α-l-rhamnopyranoside) (Figure 1). As far as we know, this is the first report on the presence of quercitrin in the fermented leaves of C. chrysantha.

Compound 2 was obtained as a yellow amorphous powder. The 1H NMR and 13C NMR spectra of 2 were close to those of 1, suggesting that it was also a flavonoid glycoside. In comparison of the data of 1H NMR, 13C NMR, HSQC and HMBC spectrum of compound 2 with those reported [10], it was identified as afzelin (Figure 1). To the best of our knowledge, this is the first report on the presence of afzelin in C. chrysantha fermented leaves.

Compound 3 was obtained as a yellow amorphous powder. The 1D and 2D NMR spectra of 3 indicated a flavan-3-ol structure. The chemical shift of the H-2 proton in compound 3 appeared as a broad singlet at δ H 4.81, suggesting a cis-2,3 configuration in the flavan structure, which has been known as a characteristic of epicatechin [11]. By comparing 1H NMR, 13C NMR, HSQC and HMBC data of compound 3 with those in the literature [12], the compound was identified as (-)-epicatechin (Figure 1). Previously, epicatechin was repoted as a component of Camellia sinensis, showing antimicrobial, anti-inflammatory, and antioxidant activities [13], [14], [15]. Epicatechin has also been isolated from the leaves of C. chrysantha [16], but the presence of epicatechin in the fermented leaves of this species has not been mentioned elsewhere.

Compound 4 was obtained as a yellow powder. The NMR spectra implied that this compound is a flavonoid glycoside. Comparison with those reported [17], the data of 1H NMR, 13C NMR, HSQC and HMBC spectra indicated that 4 was an engelitin (dihydrokaempferol 3-O-α- l -rhamnopyranoside) (Figure 1). Noteworthy, the presence of engelitin in fermented C. chrysantha leaves has not been reported previously.

Four isolated compounds were then evaluated for their antioxidative activity against DPPH and ABTS, as well as α-glucosidase inhibitory activity in substrate pNPG. The percentage of scavenging capacity and SC50 values of these compounds were determined and recorded in Tables SVI-1 and SVI-2.

As evaluated by DPPH assay, two compounds, i.e. quercitrin (1) and (-)-epicatechin (3) were found to exhibit SC percentages exceeding 50 %, with SC50 values of 52.38 ± 0.4 and 28.74 ± 0.28 μg/mL, respectively. Regarding the ABTS assay’s test result, all tested compounds 1–4 showed scavenging capacity with SC50 values ranging from 8.81 ± 0.21 to 57.54 ± 0.18 μg/mL. Of these compounds, compound 3 possessed the highest scavenging capacity (95.01 ± 0.27 % against ABTS), with SC50 value of 8.81 ± 0.21 μg/mL. As revealed in Table SVI-2, afzelin (2) was the sole exhibiting significant α-glucosidase inhibition with IC50 value of 78.25 ± 0.88 μg/mL.

Discussion

In general, the scavenging capacities as determined by ABTS assay represented a higher variation than in the DPPH assay of approximately 1.5-fold. Diverse scavenging properties resulted from these has been previously reported.

Quecitrin, epicatechin and engelitin as flavonol compounds have been found in plants, playing a crucial role in protecting cells against oxidative stress. Results revealed from our study showed less antioxidative potencies of quecitrin and epicatechin compared to positive control (ascorbic acid). Possibly, extracellular enzymes produced by E. cristatum, were responsible for enhancing the oxidation, degradation, and transformation of phenolic compounds, allowing the stabilization and relocation of unpaired electrons in their structure, thus facilitating the donation of hydrogen atoms and electrons from their hydroxyl groups. During the fermentation, thearubigins (TRs), which may be formed by polyphenols, such as (−)-epigallocatechin gallate (EGCG) and (−)-epicatechin (EC), were considered potential activities that included anti-inflammatory, anticancer, antiobesity, antiosteoporotic, and antimicrobial properties [18].

Afzelin (kaempferol 3-O-rhamnoside) is known as a flavonoid glycoside, found in several plant species and dark teas (i.e., Pu-erh tea, Qingzhuan tea, Liubao tea, Kangzhuan tea) [19]. Previous study of the afzelin biosynthesis pathway revealed a synthesis from kaempferol by kaempferol 3-O-rhamnosyl transferase [20]. Studies indicated diverse bioactivities of afzelin, including antioxidants, anti-inflammatory, neuroprotective, anticancer and α-glucosidase inhibitory. According to Torres-Naranjo et al. (2016), afzelin inhibited α-glucosidase significantly with an IC50 value of 3.56 μM [21]. According to Lee et al. (2018), afzelin possessed α-glucosidase inhibitory activity with an IC50 value of 1.13 μg/mL [22]. However, afzelin in previous studies was reported with origins from endemic plant species (i.e., Lespedeza cuneate, Agrimonia pilosa Ledeb, Muehlenbeckia tamnifolia). In this work, afzelin was isolated for the first time from fermented leaves of C. chrysantha (Bache, Quangninh) which was facilitated by solid-state fermentation with the aid of E. cristatum. Gu et al. (2019) stated that the flavonoids glycosides (e.g., quercetin, kaempferol, and isorhamnetin) contents in herbal leaves fermented by Eurotium sp. increased significantly [23]. After seven days, kaempferol contents in fermented and non-fermented HRL were detected to be 85.24 ± 1.62 and 11.02 ± 0.05 (mg/100 g dry leaf), respectively.

Conclusions

Given the results obtained in this study, four flavonoids, including quercitrin (1), afzelin (2), (-)-epicatechin (3), and engelitin (4) were isolated from fermented leaves of Camellia chrysantha by E. cristatum. It is the first report on the presence of these compounds in the Camellia chrysantha fermented leaves. While all compounds 1–4 exhibited antioxidative activity in ABTS assay, barely compounds 1 and 3 demonstrated scavenging properties against DPPH. Compound (2) was the sole exhibiting α-glucosidase inhibitory capacity. The investigation provides information regarding chemical composition and bioactivities of microbial fermented leaves of C. chrysantha, which may applicable as a promising therapeutic accession to cure oxidative stress and diabetes.

Corresponding author: Van Thi Hong Nguyen, Institute of Natural Products Chemistry (INPC), Vietnam Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Cau Giay, Hanoi 10072, Vietnam; and Graduate University of Science and Technology, Vietnam Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Cau Giay, Hanoi 10072, Vietnam, E-mail:

Funding source: Vietnam Academy of Science and Technology

Award Identifier / Grant number: VAST02.01/22-23

  1. Research ethics: The local Institutional Review Board deemed the study exempt from review.

  2. Informed consent: Informed consent was obtained from all individuals included in this study.

  3. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.

  4. Use of Large Language Models, AI and Machine Learning Tools: None declared.

  5. Conflict of interest: Authors state no conflict of interest.

  6. Research funding: This work was supported by by the Vietnam Academy of Science and Technology (VAST) under grant number VAST02.01/22-23.

  7. Data availability: Not applicable.

References

1. Diep, TT. Yellow camellias: a review of chemical constituents and biological activities. Dalat Univ J Sci 2022:117–44. https://doi.org/10.37569/dalatuniversity.12.3.977(2022).Search in Google Scholar

2. Wei, JB, Li, X, Song, H, Liang, YH, Pan, YZ, Ruan, JX, et al.. Characterization and determination of antioxidant components in the leaves of Camellia chrysantha (Hu) Tuyama based on composition-activity relationship approach. J Food Drug Anal 2015;23:40–8. https://doi.org/10.1016/j.jfda.2014.02.003.Search in Google Scholar PubMed PubMed Central

3. Villarreal-Soto, SA, Beaufort, S, Bouajila, J, Souchard, JP, Taillandier, P. Understanding Kombucha tea fermentation: a review. J Food Sci 2018;83:580–8. https://doi.org/10.1111/1750-3841.14068.Search in Google Scholar PubMed

4. Hur, SJ, Lee, SY, Kim, YC, Choi, I, Kim, GB. Effect of fermentation on the antioxidant activity in plant-based foods. Food Chem 2014;160:346–56. https://doi.org/10.1016/j.foodchem.2014.03.112.Search in Google Scholar PubMed

5. Dabhi, AS, Bhatt, NR, Shah, MJ. Voglibose: an alpha glucosidase inhibitor. J Clin Diagn Res 2013;7:3023–7. https://doi.org/10.7860/JCDR/2013/6373.3838.Search in Google Scholar PubMed PubMed Central

6. Brand-Williams, W, Cuvelier, ME, Berset, CLWT. Use of a free radical method to evaluate antioxidant activity. LWT--Food Sci Technol 1995;28:25–30. https://doi.org/10.1016/s0023-6438(95)80008-5.Search in Google Scholar

7. Chi, HK, Ha, TTH, Hung, TN, Hang, TTN, Tham, TTH, Huong, LM, et al.. Screening of algae collected from Nha Trang bay, Vietnam, for potential cosmeceutical bioproducts. Vietnam J Marine Sci Technol 2022;22:415–22. https://doi.org/10.15625/1859-3097/18020.Search in Google Scholar

8. Tadera, K, Minami, Y, Takamatsu, K, Matsuoka, T. Inhibition of alpha-glucosidase and alpha-amylase by flavonoids. J Nutr Sci Vitaminol 2006;52:149–53. https://doi.org/10.3177/jnsv.52.149.Search in Google Scholar PubMed

9. Zhong, XN, Otsuka, H, Ide, T, Takushi, A, Takeda, Y. Three flavonol glycosides from leaves of Myrsine seguinii. Phytochemistry 1997;46:943–6. https://doi.org/10.1016/s0031-9422(97)00366-x.Search in Google Scholar

10. Chaturvedula, VSP, Prakash, I. Kaempferol glycosides from Siraitia grosvenorii. J Chem Pharm Res 2011;3:799–804.Search in Google Scholar

11. Shen, CC, Chang, YS, Hott, LK. Nuclear magnetic resonance studies of 5,7-dihydroxyflavonoids. Phytochemistry 1993;34:843–5. https://doi.org/10.1016/0031-9422(93)85370-7.Search in Google Scholar

12. Davis, AL, Cai, Y, Davies, AP, Lewis, J. 1H and 13C-NMR assignments of some green tea polyphenols. Magn Reson Chem 1996;34:887–90. https://doi.org/10.1002/(sici)1097-458x(199611)34:11<887::aid-omr995>3.0.co;2-u.10.1002/(SICI)1097-458X(199611)34:11<887::AID-OMR995>3.0.CO;2-USearch in Google Scholar

13. Reygaert, WC. The antimicrobial possibilities of green tea. Front Microbiol 2014;5:434–8. https://doi.org/10.3389/fmicb.2014.00434.Search in Google Scholar

14. Bettaieb, A, Cremonini, E, Kang, H, Kang, J, Haj, FG, Oteiza, PI. Anti-inflammatory actions of (-)-epicatechin in the adipose tissue of obese mice. Int Biochem Cell Biol 2016;81:383–92. https://doi.org/10.1016/j.biocel.2016.08.044.Search in Google Scholar

15. Scott, BC, Butler, J, Halliwell, B, Aruoma, OI. Evaluation of the antioxidant actions of ferulic acid and catechins. Free Radic Res Commun 1993;19:241–53. https://doi.org/10.3109/10715769309056512.Search in Google Scholar

16. Wei, JB, Li, X, Song, H, Liang, YH, Pan, YZ, Ruan, JX, et al.. Characterization and determination of antioxidant components in the leaves of Camellia chrysantha (Hu) Tuyama based on composition-activity relationship approach. J Food Drug Anal 2015;23:40–8. https://doi.org/10.1016/j.jfda.2014.02.003.Search in Google Scholar

17. Choi, J, Cho, JY, Kim, YD, Htwe, KM, Lee, WS, Lee, JC, et al.. Phenolic compounds and triterpenes from the barks of Diospyros burmanica. Nat Prod Sci 2015;21:76–81.Search in Google Scholar

18. Long, PP, Rakariyatham, K, Ho, CT, Zhang, L. Thearubigins: formation, structure, health benefit and sensory property. Trends Food Sci Technol 2023;133:37–48. https://doi.org/10.1016/j.tifs.2023.01.013.Search in Google Scholar

19. Cheng, LZ, Wang, YF, Zhang, JR, Xu, LR, Zhou, H, Wei, K, et al.. Integration of non-targeted metabolomics and E-tongue evaluation reveals the chemical variation and taste characteristics of five typical dark teas. LWT-Food Sci Technol 2021;150:111875. https://doi.org/10.1016/j.lwt.2021.111875.Search in Google Scholar

20. Mediani, A, Hamezah, HS, Rohani, E, Kamal, N, Perumal, V, Salim, F, et al.. Afzelin: advances on resources, biosynthesis pathway, bioavailability, bioactivity, and pharmacology. In: Xiao, J, editor. Handbook of Dietary Flavonoids. Cham: Springer; 2023:1–45 pp.10.1007/978-3-030-94753-8_63-1Search in Google Scholar

21. Torres-Naranjo, M, Suárez, A, Gilardoni, G, Cartuche, L, Flores, P, Morocho, V. Chemical constituents of Muehlenbeckia tamnifolia (Kunth) Meisn (Polygonaceae) and its in vitro α-amilase and α-glucosidase inhibitory activities. Molecules 2016;21:1461. https://doi.org/10.3390/molecules21111461.Search in Google Scholar

22. Lee, J, Lee, DG, Rodriguez, JP, Park, JY, Cho, EJ, Jacinto, SD, et al.. Determination of flavonoids in Acer okamotoanum and their aldose reductase inhibitory activities. Hortic Environ Biotechnol 2018;59:131–7. https://doi.org/10.1007/s13580-018-0014-2.Search in Google Scholar

23. Gu, Q, Duan, G, Yu, X. Bioconversion of flavonoid glycosides from hippophae rhamnoides leaves into flavonoid aglycones by Eurotium amstelodami. Microorganisms 2019;7:122. https://doi.org/10.3390/microorganisms7050122.Search in Google Scholar PubMed PubMed Central

Supplementary Material

This article contains supplementary material (https://doi.org/10.1515/tjb-2024-0198).

Received: 2024-08-21
Accepted: 2024-11-30
Published Online: 2025-05-23

© 2025 the author(s), published by De Gruyter, Berlin/Boston

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/tjb-2024-0198
Keywords for this article
Camellia chrysantha; fermented leaves; flavonoids; antioxidant; α-glucosidase
Creative Commons
BY 4.0

Articles in the same Issue

  1. Frontmatter
  2. Review Article
  3. Unveiling the hidden clinical and economic impact of preanalytical errors
  4. Research Articles
  5. To explore the role of hsa_circ_0053004/hsa-miR-646/CBX2 in diabetic retinopathy based on bioinformatics analysis and experimental verification
  6. Study on the LINC00578/miR-495-3p/RNF8 axis regulating breast cancer progression
  7. Comparison of two different anti-mullerian hormone measurement methods and evaluation of anti-mullerian hormone in polycystic ovary syndrome
  8. The evaluation of the relationship between anti angiotensin type I antibodies in hypertensive patients undergoing kidney transplantation
  9. Evaluation of neopterin, oxidative stress, and immune system in silicosis
  10. Assessment of lipocalin-1, resistin, cathepsin-D, neurokinin A, agmatine, NGF, and BDNF serum levels in children with Autism Spectrum Disorder
  11. Regulatory nexus in inflammation, tissue repair and immune modulation in Crimean-Congo hemorrhagic fever: PTX3, FGF2 and TNFAIP6
  12. Pasteur effect in leukocyte energy metabolism of patients with mild, moderate, and severe COVID-19
  13. Thiol-disulfide homeostasis and ischemia-modified albumin in patients with sepsis
  14. Myotonic dystrophy type 1 and oxidative imbalance: evaluation of ischemia-modified albumin and oxidant stress
  15. Antioxidant and alpha-glucosidase inhibitory activities of flavonoids isolated from fermented leaves of Camellia chrysantha (Hu) Tuyama
  16. Examination of the apelin signaling pathway in acetaminophen-induced hepatotoxicity in rats
  17. Integrating network pharmacology, in silico molecular docking and experimental validation to explain the anticancer, apoptotic, and anti-metastatic effects of cosmosiin natural product against human lung carcinoma
  18. Validation of Protein A chromatography: orthogonal method with size exclusion chromatography validation for mAb titer analysis
  19. The evaluation of the efficiency of Atellica UAS800 in detecting pathogens (rod, cocci) causing urinary tract infection
  20. Case Report
  21. Exploring inherited vitamin B responsive disorders in the Moroccan population: cutting-edge diagnosis via GC-MS profiling
  22. Letter to the Editor
  23. Letter to the Editor: “Gene mining, recombinant expression and enzymatic characterization of N-acetylglucosamine deacetylase”
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