Online Liquid Microextraction Coupled with HPLC-ABTS for Rapid Screening of Natural Antioxidants: Case Study of Three Different Teas

Screening Antioxidant Components in Different Parts of Dandelion Using Online Gradient Pressure Liquid Extraction Coupled with High-Performance Liquid Chromatography Antioxidant Analysis System and Molecular Simulations

Utilizing online gradient pressure liquid extraction (OGPLE) coupled with a high-performance liquid chromatography antioxidant analysis system, we examined the antioxidative active components present in both the aerial parts and roots of dandelion. By optimizing the chromatographic conditions, we identified the ferric reducing-antioxidant power system as the most suitable for online antioxidant reactions in dandelion. Compared to offline ultrasonic extraction, the OGPLE method demonstrated superior efficiency in extracting chemical components with varying polarities from the samples. Liquid chromatography-mass spectrometry revealed twelve compounds within the dandelion samples, with nine demonstrating considerable antioxidant efficacy. Of these, the aerial parts and roots of dandelion contained nine and four antioxidant constituents, respectively. Additionally, molecular docking studies were carried out to investigate the interaction between these nine antioxidants and four proteins associated with oxidative stress (glutathione peroxidase, inducible nitric oxide synthase, superoxide dismutase, and xanthine oxidase). The nine antioxidant compounds displayed notable binding affinities below -5.0 kcal/mol with the selected proteins, suggesting potential receptor-ligand interactions. These findings contribute to enhancing our understanding of dandelion and provide a comprehensive methodology for screening the natural antioxidant components from herbs.

Rapid screening and evaluation of natural antioxidants from leaf, stem, and root of Artemisia argyi by online liquid microextraction combined with HPLC-based antioxidant assay system coupled with calibration quantitative analysis

To reveal the utilization value of leaf, stem, and root of Artemisia argyi, a rapid online liquid microextraction combined with a high-performance liquid chromatography coupled with 2,2-nitrogen-di (3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt antioxidant assay system was established for analysis of antioxidants in the leaf, stem, and root of A. argyi, and a calibration quantitative method of antioxidant activity with equivalent chlorogenic acid was proposed. Thirty-three positive peaks were identified; among them, 12 compounds were found that possess good antioxidant activity including eleven organic acids (components 2-4, 8, 11-14, 17, 19, and 21) and one flavonoids (component 22). The proposed calibration quantitative method avoided the influence of content of compound and compared the extent of radical scavenging capacity of five antioxidant compounds, which were ranked as follow: 3,5-dicaffeoylquinic acid > 3,4-dicaffeoylquinic acid ≈ 4,5-dicaffeoylquinic acid > 1,4-dicaffeoylquinic acid > chlorogenic acid. In conclusion, this study provided composition and biological potential for the future development of the leaf, stem, and root of A. argyi. It is believed that the online liquid microextraction combined with high-performance liquid chromatography based antioxidant assay system can be widely used for the rapid screening of natural antioxidant components in the different parts of natural products.

Characteristics and Relationships between Total Polyphenol and Flavonoid Contents, Antioxidant Capacities, and the Content of Caffeine, Gallic Acid, and Major Catechins in Wild/Ancient and Cultivated Teas in Vietnam

Vietnam has diverse and long-established tea plantations but scientific data on the characteristics of Vietnamese teas are still limited. Chemical and biological properties including total polyphenol and flavonoid contents (TPCs and TFCs), antioxidant activities (DPPH, ABTS, FRAP, and CUPRAC), as well as the contents of caffeine, gallic acid, and major catechins, were evaluated for 28 Vietnamese teas from North and South Vietnam. Higher values of TPCs and TFCs were found for green (non-oxidised) and raw Pu'erh (low-oxidised) teas from wild/ancient tea trees in North Vietnam and green teas from cultivated trees in South Vietnam, as compared to oolong teas (partly oxidised) from South Vietnam and black teas (fully oxidised) from North Vietnam. The caffeine, gallic acid, and major catechin contents depended on the processing, geographical origin, and the tea variety. Several good Pearson's correlations were found (r² > 0.9) between TPCs, TFCs, the four antioxidant capacities, and the content of major catechins such as (-)-epicatechin-3-gallate and (-)-epigallocatechin-3-gallate. Results from principal component analysis showed good discriminations with cumulative variances of the first two principal components varying from 85.3% to 93.7% among non-/low-oxidised and partly/fully oxidised teas, and with respect to the tea origin.

Online Microextraction Coupled with HPLC-ABTS for Rapid Analysis of Antioxidants from the Root of Polygonum bistorta

The root of Polygonum bistorta (PB) is a traditional Chinese medicinal plant material widely used in China. It has been commonly used for the treatment of hemostasis, detumescence, diarrhea, snake bite, and acute gastroenteritis. However, the research on the antioxidant properties and bioactive compounds from PB is inadequate. In the current research, an online microextraction (OLME) coupled with a high-performance liquid chromatography coupled with the 2,2-nitrogen-di (3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt antioxidant assay (HPLC-ABTS) system for rapid analysis of antioxidants from PB was proposed. The PB sample (0.17 mg) was online extracted by mobile phase (acetonitrile and 0.2% acetic acid); a Poroshell 120 SB-Aq column was used for separation; then, an online ABTS assay system was used for screening the antioxidants. Finally, ten components were found in PB, and among them, eight components possessed antioxidant activities. Furthermore, five components (gallic acid, neochlorogenic acid, caffeic acid, chlorogenic acid, and an unknown compound) were proved as major antioxidants when compared with rutin as an antioxidant marker. The results showed that the developed OLME-HPLC-ABTS system was a simple, rapid, green, and efficient instrument for the screening of antioxidants from PB, which provides a powerful tool for the discovery of natural antioxidants in Chinese medicines.

Online pressurized liquid extraction enables directly chemical analysis of herbal medicines: A mini review

Extraction is responsible for transferring components from solid materials into solvent. Tedious extraction procedures are usually involved in liquid chromatography-based chemical analysis of herbal medicines (HMs), resulting in extensive consumptions of organic solvents, time, energy, and materials, as well as the significant chemical degradation risks for those labile compounds. Fortunately, an emerging online pressurized liquid extraction (OLE, also known as online liquid extraction) technique has been developed for the achievement of directly chemical analysis for solid matrices in recent years, and in a short period, this versatile technique has been widely applied for the chemical analysis of HMs. In the present mini-review, we aim to briefly summarize the principles, the instrumentation, along with the application progress of this robust and flexible extraction technique in the latest six years, and the emerging challenges and future prospects are discussed as well. Special attention is paid onto the hyphenation of the versatile OLE module with LC-MS instrument. The described information is expected to introduce a promising OLE approach and to provide the guidance for the achievement of directly chemical analysis of, but not limited to, HMs.

Evaluation of the phytochemicals and antioxidant activity of Lophatherum gracile Brongn based on chemical fingerprinting by HPLC with electrochemical detection

A combinative method using high-performance liquid chromatography-electrochemical detection for fingerprinting and quantitative analysis was developed and successfully applied for the quality evaluation of Lophatherum gracile Brongn leaves collected from 21 geographical locations in China. In the fingerprint analysis, 18 common peaks were observed among the 21 samples, and 10 peaks were identified. Simultaneous quantification of the 10 components was conducted to interpret the variations in these compounds among the L. gracile Brongn leaves originating from different geographical locations. The correlation between the chromatograms and the antioxidant activities of the samples was further studied. The results indicated a linear correlation between the antioxidant activity and the total common peak areas of the fingerprints obtained by high-performance liquid chromatography-electrochemical detection. Importantly, it was found that high-performance liquid chromatography-electrochemical detection fingerprinting can not only determine the quantities of individual components present in such samples but also evaluate the antioxidant activities of the samples. The developed method is a valuable reference for the further study and development of L. gracile Brongn.

A rapid analysis of antioxidants in Sanghuangporus baumii by online extraction-HPLC-ABTS

In the present study, a simple and efficient approach based on the online extraction-high performance liquid chromatography coupled with ABTS antioxidant assay (OLE-HPLC-ABTS) was established to quickly and directly analyze the antioxidants in S. baumii. Through this system, the HPLC mobile phase via a guard column packed with a S. baumii sample was used for online extraction (OLE). The separation was performed on an Agilent Poroshell EC-C18 column with a gradient elution using 0.1% formic acid (A) and 0.1% formic acid-acetonitrile (B) as mobile phase systems and detected at a wavelength of 254 nm. Then, the separated compounds were reacted with the antioxidant solution (ABTS), and the response was recorded at a wavelength of 400 nm. The developed analytical method was successfully applied to S. baumii samples, and eight antioxidants were identified. The established system integrated the online extraction, separation and online antioxidant detection, which is rapid, efficient, and suitable for the rapid screening of antioxidant compounds from solid sample mixtures.

Analysis of antioxidants in Chrysanthemum indici flos by online gradient extraction and HPLC-FRAP

Chrysanthemum indici flos (CIF), a traditional functional beverage, has been used in China for thousands of years. However, research on the antioxidant properties and compounds in CIF is insufficient. In the current study, an online gradient extraction (OGE) coupled with a high performance liquid chromatography-ferric reducing antioxidant power (HPLC-FRAP) system for rapid identification of antioxidants in CIF was proposed. The CIF sample (0.3 mg) was extracted online by a gradient mobile phase (acetonitrile and 0.1% formic acid), separated on a Poroshell 120 SB-Aq column, and then detected for the anti-oxidative activity with the online FRAP assay. 36 peaks were found and 28 compounds were identified. Among them, 18 peaks showed antioxidant activity, six of which were detected in CIF for the first time. The total analytical time was less than 45 min, including sample extraction, separation, and antioxidant identification. The results indicate that the OGE-HPLC-FRAP system is a simple, efficient and rapid tool for screening antioxidants in CIF, which provides the scientific data of CIF's antioxidant research and is helpful to improve the quality evaluation of CIF.