Evaluation of the antioxidant potential of brown seaweeds extracted by different solvents and characterization of their phenolic compounds by LC-ESI-QTOF-MS/MS.

Seaweeds, serving as valuable natural sources of phenolic compounds (PCs), offer various health benefits like antioxidant, anti-inflammatory properties, and potential anticancer effects. The efficient extraction of PCs from seaweed is essential to harness their further applications. This study compares the effectiveness of different solvents (ethanol, methanol, water, acetone, and ethyl acetate) for extracting PCs from four seaweed species: Ascophyllum sp., Fucus sp., Ecklonia sp., and Sargassum sp. Among them, the ethanol extract of Sargassum sp. had the highest content of total phenolics (25.33 ± 1.45 mg GAE/g) and demonstrated potent scavenging activity against the 2,2-diphenyl-1-picrylhydrazyl radical (33.65 ± 0.03 mg TE/g) and phosphomolybdate reduction (52.98 ± 0.47 mg TE/g). Ecklonia sp. had the highest content of total flavonoids (0.40 ± 0.02 mg QE/g) in its methanol extract, whereas its ethyl acetate extract contained the highest content of total condensed tannins (8.09 ± 0.12 mg CE/g). Fucus sp. demonstrated relatively strong antioxidant activity, with methanolic extracts exhibiting a scavenging ability against 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical (54.41 ± 0.24 mg TE/g) and water extracts showing ferric-reducing antioxidant power of 36.24 ± 0.06 mg TE/g. Likewise, liquid chromatography-mass spectrometry identified 61 individual PCs, including 17 phenolic acids, 32 flavonoids, and 12 other polyphenols. Ecklonia sp., particularly in the ethanol extract, exhibited the most diverse composition. These findings underscore the importance of selecting appropriate solvents based on the specific seaweed species and desired compounds, further providing valuable guidance in the pharmaceutical, nutraceutical, and cosmetic industries. PRACTICAL APPLICATION: The PCs, which are secondary metabolites present in terrestrial plants and marine organisms, have garnered considerable attention due to their potential health advantages and diverse biological effects. Using various organic/inorganic solvents during the extraction process makes it possible to selectively isolate different types of PCs from seaweed species. The distinct polarity and solubility properties of each solvent enable the extraction of specific compounds, facilitating a comprehensive assessment of the phenolic composition found in the seaweed samples and guiding industrial production.

Extraction and characterization of phenolic compounds and their potential antioxidant activities.

For thousands of years, plant has been widely applied in the medical area and is an important part of human diet. A high content of nutrients could be found in all kinds of plants, and the most outstanding group of nutrients that attracts scientists' attention is the high level of phenolic compounds. Due to the relationship between high phenolic compound content and high antioxidant capacity, plant extracts are expected to become a potential treatment for oxidation stress diseases including diabetes and cancer. However, according to the instability of phenolic compounds to light and oxygen, there are certain difficulties in the extraction of such compounds. But after many years of development, the extraction technology of phenolic compounds has been quite stable, and the only problem is how to obtain high-quality extracts with high efficiency. To further enhance the value of plant extracts, concentration and separation methods are often applied, and when detailed analysis is required, characterization methods including HPLC and LC/GC-MS will be applied to evaluate the number and type of phenolic compounds. A series of antioxidant assays are widely performed in numerous studies to test the antioxidant capacity of the plant extracts, which is also an important basis for evaluating value of extracts. This paper intends to provide a view of a variety of methods used in plants' phenolic compound extraction, separation, and characterization. Furthermore, this review presents the advantages and disadvantages of techniques involved in phenolic compound research and provides selected representative bibliographic examples.

LC-ESI-QTOF-MS/MS characterization of phenolic compounds from Pyracantha coccinea M.Roem. and their antioxidant capacity.

Pyracantha coccinea M.Roem. is considered as an important medicinal plant contributing remarkably to health and medicinal benefits. This is attributed to the presence of abundant polyphenols with powerful antioxidant properties. However, little research has been studied on the comprehensive identification and characterization of the phenolic compounds in areal parts of P. coccinea.  This study aimed to investigate, characterize, and quantify the phenolic profiles of P. coccinea through liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS/MS) and high-performance liquid chromatography-photodiode array (HPLC-PDA. Further, it showed a significantly higher value in total phenolic content (TPC) than that of total flavonoids (TFC) and tannins (TTC). As for antioxidant capacities, P. coccinea presented the highest activity in ABTS (7.12 ± 0.25 mg AAE/g dw) compared with DPPH, FRAP, and TAC assays. The LC-ESI-QTOF-MS/MS analysis detected 28 phenolic compounds, including phenolic acids (12), flavonoids (13), other polyphenols (2), and lignans (1) in P. coccinea samples. The results from HPLC-PDA indicated the chlorogenic acid (11.49 ± 1.89 mg/g) was the most abundant phenolic acid, while kaempferol (14.67 ± 2.17 mg/g) was the predominant flavonoid in P. coccinea. This research confirms the benefits of the P. coccinea plant as a potential source of natural antioxidants for the food and pharmaceutical industries.