Marine organisms are rich in bioactive substances, which have different molecular structures and biological activities. Due to their high safety, they have become research hotspots in the fields of health food, drugs and cosmetics.

Seaweeds are one of the most important biological resources in the field, whose dietary consumption is associated with a reduced risk of cardiovascular disease, hyperglycemia, and breast cancer. Seaweeds contain new and structurally diverse bioactive substances that differ from land plants, but the potential of seaweed active substances is still largely overlooked by the scientific community.

This paper will review the progress of seaweed polyphenols from the aspects of their source, chemical structure and biological activity.

Brown algae is a kind of relatively advanced large seaweed, commonly known as brown algae because of its main brown color, its large individual, high yield, wide distribution, in China along

The position of sea economic resources is significant. Polyphenolic compounds are found in brown algae, and in the current study, it was found to only exist in brown algae, so the polyphenolic compounds in seaweed phenols are also called brown algae polyphenols. Its structural unit is mesoglucinol, which is generally believed that oligos can be further polymerized to form a higher molecular weight tannin.

Brown algal polyphenols have various biological activities such as antioxidant, anti-inflammatory, anti-cancer and antibacterial activities. At the same time, brown algae polyphenols also have the effect of preventing and controlling obesity, reducing blood fat, protecting the liver and so on. Therefore, the development and utilization of brown algae polyphenols also have a high application value. As the main active substance in seaweed and has various biological activities, seaweed polyphenols are gradually being studied and explored.

Biological activity of seaweed polyphenols

Seaweed polyphenols have various biological activities, including antioxidant, antibacterial, anti-tumor, and anti-obesity, etc. Its biological activities will be summarized below in these several aspects.

1. Antioxidant activity

Scientific research has shown that cancer, aging or other diseases are mostly associated with the production of excessive free radicals. Seaweed polyphenols are natural antioxidants that scavenge free radicals and chelate metal ions. Some scholars have shown that the antioxidant effect of polyphenols is related to its extraction solvent. For example, O'SULLIVAN et al. proved that the total phenolic antioxidant activity of methanol extract from F.vesiculosus (60%) is better than other extracts; LOPEZ and others found that the DPPH clearance of seaweed polyphenols with water as solvent (47.9%) is higher than that of seaweed polyphenols with ethanol as solvent (17.0%).

Because of these antioxidant properties, seaweed polyphenols in pharmaceutical, nutrition, cosmetics and other fields has the great potential to develop new antioxidant products, at the same time studies have been shown that the introduction of seaweed polyphenols extract in food can effectively play the role of rancidity inhibitor / retarder, thus help to improve its shelf life, and become a good candidate for the development of natural food additives.

2. Biostatic activity

Antibiotics have been widely used and resistant bacteria are increasing, and the development of new anti-bacterial drugs has become a global concern. Alweed polyphenols have obvious inhibitory effects on a variety of bacteria, such as bacteria, fungi, yeast, as well as some common pathogenic bacteria. The phenolic hydroxyl group in brown algae polyphenols can promote the passage of polyphenols, enhance the interference of polyphenols on bacterial cell membrane structure and function, and destroy the integrity of bacterial cell membrane, thus exerting antibacterial effect. Using plate growth inhibition method of the polyphenolic compounds, concluded that in a certain concentration range of the components of V. haemolyticus, V. harvei, silkworm, Staphylococcus aureus, E. coli, V. eel, V. alginolyticus and quadruple micrococcus test strains have antibacterial activity.

In addition to the studies on bacteria, other studies have shown the inhibitory effect of brown algae polyphenols on fungi. LEE et al studied the antimicrobial activity of Dieckol polyphenols purified from E. cava and found that it showed effective antifungal activity against Trichoptis rubrum associated with human skin nail infection. Furthermore, it showed potent inhibition of cell membrane integrity as well as cell metabolism in T. rhoorus. Numerous studies have proved that brown algal polyphenols have good antibacterial effect. Although different microorganisms have different sensitivity to brown algae polyphenols, the dosage-effect relationship of bacteria on polyphenols is dose-dependent. Therefore, it can be developed into a highly efficient antibacterial agent.

3. Antitumtumor activity

Tumor refers to the genetic change of cells under the action of carcinogenic factors, and the loss of normal regulation of its growth, leading to dysplasia. Seaweed polyphenols inhibit the growth of tumor cells mainly by scavenging free radicals and inhibiting the gene expression of tumor cells and enhancing immune pathways. However, there are some differences in the inhibitory effect of tumor cells by different seaweed sources. Wang Changxiu et al. studied the antitumor effect of S180 tumor-bearing mice in vivo, and concluded that it had obvious antitumor effect, and speculated that the mechanism might be by improving immune and antioxidant capacity.

Lu Hongyu et al. found that the polyphenol extract of whole sargassum with different polarity and molecular weight had different inhibition effect on thyroid cancer cells (sw 579) and was correlated with concentration; the inhibition rate of large molecular weight extract was higher than that of small molecular weight extract, and the highest inhibition rate could reach more than 90%. A large number of studies have proved that seaweed polyphenols have anti-proliferative effects on liver cancer cell lines, breast cancer cell lines, pancreatic cancer cell line, cervical cancer cell line, lung cancer cell line, colon cancer cell line, etc.

4. Anti-obesity activity

Obesity is considered one of the most common metabolic diseases and constitutes a growing global public health problem for [58]. Obesity occurs when there is an imbalance between energy intake and energy expenditure, and obesity is characterized by the overgrowth and development of adipose tissue. It has been shown that reducing obesity is effective in improving the risk of developing type II diabetes. KO et al. found that Dieckol (brown algae polyphenols extracted from methanol) could effectively inhibit 3T3-L1 preadipocyte generation through the activation of AMPK, proving the anti-obesity activity of seaweed polyphenols.

TADASHI From E.kurome found a new polyphenol extract inhibiting peptidyl prolyl isomerase. 974-B (molecular weight 974Da) can effectively block the differentiation of fibroblasts into adipocytes, and speculated that 974-B could serve as a starting point for the development of drugs for obesity-related diseases, including diabetes, hypertension and non-alcoholic steatohepatitis. AUSTIN And so on studied the inhibitory activity of the polyphenol-rich extract of edible seaweed on lipase, proved that the polyphenol components significantly inhibit lipase in vitro, and suggested that the conclusion that the inhibitory lipase activity may be enhanced when the polyphenol components interact with sugar binding.

5. Other

In addition, brown algae polyphenols can also prevent UV damage by fighting oxidation, inhibiting apoptosis, and inhibiting DNA damage. Ultraviolet light can cause UV damage to human skin through oxidation. Brown algae polyphenols are a natural strong antioxidant and have broad development prospects in anti-UV damage products. Zeng found that the protective and repair effects of polyphenols on fibroblasts irradiated with UV decreased with the increase of polyphenols concentration, with the strongest protective and repair effects at the concentration of 90 μg/mL and 80 μg/mL, respectively. Furthermore, sheep cabbage polyphenols enhanced the activity of superoxide dismutase and glutathione peroxidase and decreased the malondialdehyde content in UV-irradiated mouse fibroblasts.

Seaweed polyphenols rich source, has broad prospects for development, the research status, the present research on the biological activity, in the seaweed polyphenols antioxidant, antibacterial, anticoagulant, anti-inflammatory, anti-tumor, anti-diabetes, anti-obesity, AIDS and enzyme inhibition has achieved certain results. However, due to the complex structure and easy oxidation of seaweed, the research on their structural characteristics is still in the primary stage. The various biological activities of seaweed polyphenols are closely related to the complexity of its structure, but due to the complexity of its structure, the structural information of seaweed polyphenols is still unclear.

In research, most bioactivity studies have been conducted on non-humans, including in vitro and in vivo animal models, but the applicability and safety of seaweed polyphenols as drugs need to be further studied due to the different catalytic centers of enzymes and the complexity of the organisms. The great potential of seaweed polyphenols in biology cannot be ignored and deserves further exploration and research.