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ABSTRACT

Antioxidants are chemical compounds that bind to free oxygen radicals and break the chain of free radicals formation. It is used in effective defense mechanisms, which reduce the oxidation rate, balance the harmful ROS system, and preventing cell damage. Natural antioxidants are becoming famous in the nutraceuticals and pharmaceuticals industries nowadays. Seaweeds are the potential free radical reducing marine resources decreasing the health risk and boost oxidative stability. They are producing different kinds of antioxidant compounds as their secondary metabolites which are responsible for biological properties such as antioxidant, antimicrobial, anticancer, and antiviral activity to promote the health status of humans. Consuming the natural antioxidants provides additional benefits due to their zero side effects.

Keywords: Seaweeds, Antioxidant, Free radicals

Cite this article as: 

 

Chellamanimegalai, Iburahim, and Deshmukhe (2021)The antioxidant potentials of seaweed resources. Food and Scientific Reports. 2 (10): 14-18.

 

Seaweeds play an essential role in the food chain and the ecological stability of the intertidal ecosystem. Most of the marine organisms such as macroalgae, coral reefs, sponges and their associated organisms, are well-known for their secondary metabolites production and their bioactive compounds that increase their value towards many industries like food, neutraceuticals and pharmaceuticals etc. Among these, seaweeds have a significant role provides many phytochemicals that are responsible for antioxidant, antimicrobial, anticancer, and antiviral activity to promote the health condition (Ngo et al., 2012). There are more than 20,000 species recorded worldwide. It has been used as sea vegetables in south Asian countries like China, Japan and Korea. Since, 841 species have been recorded from India, which includes 434, 191, and 216 species of red, brown, and green seaweeds, respectively (Oza and Zaidi, 2001). Based on the analysis from Web of Science database search using keywords Seaweed or seaweeds which yielded total of 16,275 publications between 1991-2020. 

                The research output related to Seaweeds in the past 3 decades (1991 to 2020) are increasing with the tremendous growth rate in various fields from several top countries  (Fig1& 2). At present, seaweed`s antioxidant property is a widely concerned topic due to the occurrence of various diseases caused by oxidative stress. Demand for antioxidants in the food and pharmaceutical industry has been succeeded by the usage of synthetic antioxidants such as butylated hydroxytoluene (BHT), tetra-butyl hydroquinone (TBHQ), and butylated hydroxyanisole (BHA). However, natural antioxidants have irreplaceable health benefits. This article will be exclusively discussed the potential antioxidant activity of various seaweeds to increase their utilization.

 Secondary metabolites of seaweeds

                Seaweeds are a complex and heterogeneous macroalgal group. It is characterized as red, green and brown algae based on their primary photosynthetic pigments. These groups are widely dispersed and extended their distribution from temperate to tropical regions by tolerating diverse environmental conditions. Since, many types of seaweed are accidentally introduced into different places from their native, through the exchange of ballast water during the shipping activity. In that case, they need to face a sudden change in their newly entered environment such as the alteration of temperature, salinity and other water quality parameters. Most marine organisms, including seaweeds, are secreting secondary metabolites when there is a minor fluctuation in the marine environment due to the seasonal changes and climate changes etc. that makes the response to any stress factors. Antioxidant compounds are important metabolites that served as protective agents from various stress factors like temperature, UV radiations, desiccation, and pollutants (Bhattacharjee and Islam, 2014). These secondary metabolite products (phytochemicals) are accumulated in the cells, which helps to improve their adaptation to survive in the new environment, provides potential bioactive properties, help in protecting them from their competitors and predators. Tropical seaweeds have possible bioactive complexes as well as antioxidant properties than those reported from higher latitudes (Vasconcelos et al., 2019).

The role of Antioxidants

                Several health issues have been occurred due to the disintegration of cells, damage of membrane protein, DNA mutation. The primary reason behind this is an oxidation process caused by free radicals or reactive oxygen species (ROS). These reactions are indirectly promotes ageing and also generates the diseases like diabetes, liver injury, skin inflammation, coronary diseases, arthritis, arteriosclerosis, and cancer in human (Bhattacharjee and Islam, 2014). The oxidation process can be stopped by the use of antioxidant compounds that reaction is given as follows. Free radicals consist of one or more unpaired electrons in their outer layer, which needs to absorb electrons from other substances to accomplish neutrality. Altogether, another free radical or ROS is formed in the process, resulting in the chain reaction (Dontha, 2016). Reactive Oxygen species is an array of metabolites made from molecular oxygen (O2). When the concentration of ROS exceeds their limit, there will be an imbalance condition between the production of free radicals and reactive metabolites, known as "Oxidative stress". This harms the cell structure, including lipids, membrane, protein, and nucleic acids (Balakrishnan et al., 2014). Antioxidants are chemical compounds that bind to free oxygen radicals and break the chain of free radicals formation. It is used in effective defence mechanisms, which reduces the oxidation rate, balances the harmful ROS system, and preventing cell damage. For example, α-tocopherol, ascorbic acid, phenolic acids (trans-cinnamic acid, benzoic acid, and hydroxycinnamic acid), coumarins, lignans, flavonoids, isoflavonoids, and tannins (phenolic polymers) are the effective antioxidants.

 Methodology

Assessment of antioxidant activity

The antioxidant activity of seaweeds can be determined by quantifying the free radical reducing ability of seaweeds. There are several antioxidant assays used in the assessment. These assays are broadly classified into two types based on the chemical reaction that occurred between the antioxidant compounds and the free radicals (Dontha, 2016).

 

1. Hydrogen atom transfer reaction-based assays (HAT assays)

2. Electron transfer reaction-based assays (ET assays)

                HAT based assays measure the Hydrogen atom donating ability and the chain breaking ability of the antioxidant compounds. Here the reaction between the synthetic-free radical generator, oxidisable molecular probe and an oxidant to be evaluated. HAT based assays include oxygen radical absorbance capacity (ORAC), ABTS radical scavenging method, TRAP assay, Hydroxyl radical scavenging activity and β-carotene linoleic acid assay etc.

                ET based assays quantify the reducing ability of antioxidant compounds. This is the simple redox reaction that takes place when the free radicals are reduced by antioxidant compounds and get themselves oxidized. Here the colour change of the reagent is taken as the endpoint. DPPH free radical scavenging assay, superoxide anion radical scavenging assay, Ferric ion reducing antioxidant power assay (FRAP), TEAC using ABTS, CUPRAC assay and Folin-Ciocalteu reagent assay are coming under this ET based assays category. Among those free radical scavenging methods, two methods are much popular.

 1. DPPH method is simple and inexpensive when compared to other methods.

2. ABTS assay can be used for both hydrophilic and lipophilic antioxidants. 

 Phytochemicals of seaweeds for reducing free radicals

                Phytochemical compounds are the primary group of natural antioxidants in seaweeds having a significant bioactive property which includes total phenolic, flavonoid, terpenoids, polysaccharides, anthocyanin, carotenoid, peptides, halogenated ketone, alkanes, sterols and sulphur-nitrogen heterocyclics (Ling et al., 2015). The major antioxidant compounds derived from seaweeds and their biological properties are given in (table 1). Phenolic compounds such as phlorotannins, fucoxanthin, polyphenols and phylopheophylin, are the primary complex that determines the efficiency of antioxidant activity in seaweeds. Many studies reported the direct relationship between total phenolic content and free radical scavenging activity. The different methods are being followed for extracting the phenolic compounds in which the soxhlet method and methanol solvent are more effective than the conventional extraction methods (Foon et al., 2013). 

Table 1: Antioxidant compounds from macroalgal sources and their bioactive properties

Source: Bhattacharjee and Islam, 2014

                Carotenoids have been identified as the central part to reduce oxidative stress (Vasconcelos et al., 2019). Polyphenols are the kind of phytochemicals distributed deeply in all plants including marine floras which responsible for the antioxidant activity and stabilization of lipid peroxidation. These polyphenols are a significant contributor to scavenging activity than carotenoids compounds (Vijayabaskar and Shiyamala, 2012). The polyphenols present in green seaweeds are classified as catechin, epicatechin, epigalloctechin and gallic acids (Vinayak et al., 2011). Phlorotannins are phenolic compounds, consists of eight rings in their structure that exhibits the highest antioxidant activity than terrestrial plants of four rings building. These are abundantly found in some brown algal families such as Fucaceae, Alariaceae and Sargassaceae. The isolation of phlorotannins from Cystoseira trinodis has been obtained for the first time, revealed that the identification of particular compounds is essential for effective utilization (Sathya et al., 2017). Phlorotannins were also responsible for other bioactivities like antibacterial, chemopreventive, UV-protective, and antiproliferative effects (Balakrishnan et al., 2014).

                Polysaccharides compounds from various seaweeds have been reported with potential antioxidant activity (Mahendran and Saravanan, 2013). These polysaccharides are occurring in different forms in each macroalgal group; carrageenans and agar from red algae, fucoidans, laminarian and alginates from brown algae and galactans, mannans and xylans from green algae (Venkatesan et al., 2019). Carrageenans (kappa, iota and lambda type), fucoidans (homofucans) and fucans (heterofucans) are examples of the sulfated polysaccharides which can be obtained from Gigartina acicularis (lambda type), G. pisillata (lambda type), Euchema cottonii (kappa type), and E. spinosa (iota type). Fucus vesiculosus (fucoidans) and Padina gymnospora (fucans). Among those, fucoidans and lambda carrageenan has been observed with the highest antioxidant activity (de Souza et al., 2007).

 Antioxidant activity of different seaweeds

                Antioxidant activity of some important seaweed is given below (Reference: Roy, 2020).

Benefits of antioxidants

                Phytochemicals compounds contain several capabilities such as radical scavenging capacity, lipid peroxidation inhibition, metal ion chelating capacity, and reducing the power of tissue or drug that accountable for antibacterial, antifungal, antiprotozoal, antifertility, antiviral, anticancer and antimalarial activities (Vinayak et al., 2011).

Also, Seaweeds have a lot of biological properties such as anticoagulants, antioxidants, antitumors and immunomodulatory effects. Some of them are used as mosquitocidal agents. These natural antioxidants have no side effects that can be served as the best alternatives to synthetic antioxidants like BHA, PG, PHT and TBHQ (Mahendran and Saravanan, 2013). Seaweeds are used as neutraceuticals supplements, which prevent chronic diseases in humans by preventing oxidative damages (Dontha, 2016). The advantages of antioxidants are given below:

·   Support kidney function

·   Improve reproductive function

·   Maintain good dental health

·   Improve nervous system function

·   Have an anti-ageing effect

·   Protect the liver

·   Support the immune system

·   Improve the defence power of the body

·   Reduce obesity

·   Offer protection against the digestive disorder

·   Maintain healthy vision

·   Improve the quality of sleep

·   Support respiratory system

Conclusion

                Seaweeds have owned for the potential free radical reducing abilities provide a lot of benefits to humans by preventing cell damage in the oxidation process. The antioxidant compounds derived from seaweeds are purely natural and non-toxic that should be commercialized in the neutraceuticals industry (like FucoXanThin supplements) for effective consumption. We should concentrate on making functional foods enriched in natural antioxidant compounds to increase the health status of consumers. In that case, more awareness needs to be created among the local people and the pharmaceutical industries.

References

 

Balakrishnan, D., Kandasamy, D. and Nithyanand, P., (2014). A review on antioxidant activity of marine organisms. Int. J. Chem. Tech. Res, 6(7), pp.3431-3436.

Bhattacharjee, S. and Islam, G.M.R., (2014). Seaweed antioxidants as novel ingredients for better health and food quality: bangladesh prospective. Proc Pak Acad Sci, 51, pp.215-233.

de Souza, M.C.R., Marques, C.T., Dore, C.M.G., da Silva, F.R.F., Rocha, H.A.O. and Leite, E.L., (2007). Antioxidant activities of sulfated polysaccharides from brown and red seaweeds. Journal of applied phycology, 19(2), pp.153-160.

Dontha, S., (2016). A review on antioxidant methods. Asian J. Pharm. Clin. Res, 9(2), pp.14-32.

Foon, T.S., Ai, L.A., Kuppusamy, P., Yusoff, M.M. and Govindan, N., (2013). Studies on in-vitro antioxidant activity of marine edible seaweeds from the east coastal region of Peninsular Malaysia using different extraction methods. Journal of Coastal Life Medicine, 1(3), pp.193-198.

Ling, A.L.M., Yasir, S., Matanjun, P. and Bakar, M.F.A.,(2015). Effect of different drying techniques on the phytochemical content and antioxidant activity of Kappaphycus alvarezii. Journal of Applied Phycology, 27(4), pp.1717-1723.

Mahendran, S. and Saravanan, S., (2013). Purification and in vitro antioxidant activity of polysaccharide isolated from green seaweed Caulerpa racemosa. Int J Pharm Bio Sci, 4(4), pp.1214-1227.

Ngo, D. H., Vo, T. S., Ngo, D. N., Wijesekara, I., and Kim, S. K. (2012). Biological activities and potential health benefits of bioactive peptides derived from marine organisms. Int. J. Biol. Macromol. 51, 378–383. doi: 10.1016/j.ijbiomac.2012.06.001

Oza R.M. & Zaidi S.H., (2001). A Revised checklist of Indian marine algae. Central Salt and Marine Chemicals Research Institute, Bhavnagar, 296 pp.

Sathya, R., Kanaga, N., Sankar, P. and Jeeva, S., 2017. Antioxidant properties of phlorotannins from brown seaweed Cystoseira trinodis (Forsskål) C. Agardh. Arabian Journal of Chemistry, 10, pp.S2608-S2614.

Roy, S., (2020). Screening and Partial Characterization of Natural Antioxidants from Seaweeds Collected From, Rameshwaram Southeast Coast of India, Journal of Marine Science Research and Oceanography. 3(1), pp. 1-12.

Vasconcelos, J.B., de Vasconcelos, E.R., Urrea-Victoria, V., Bezerra, P.S., Reis, T.N., Cocentino, A.L., Navarro, D.M., Chow, F., Areces, A.J. and Fujii, M.T., (2019). Antioxidant activity of three seaweeds from tropical reefs of Brazil: potential sources for bioprospecting. Journal of Applied Phycology, 31(2), pp.835-846.

Venkatesan, M., Arumugam, V., Pugalendi, R., Ramachandran, K., Sengodan, K., Vijayan, S.R., Sundaresan, U., Ramachandran, S. and Pugazhendhi, A., (2019). Antioxidant, anticoagulant and mosquitocidal properties of water soluble polysaccharides (WSPs) from Indian seaweeds. Process Biochemistry, 84, pp.196-204.

Vijayabaskar, P. and Shiyamala, V., (2012). Antioxidant properties of seaweed polyphenol from Turbinaria ornata (Turner) J. Agardh, 1848. Asian Pacific Journal of Tropical Biomedicine, 2(1), pp.S90-S98.

Vinayak, R.C., Sabu, A.S. and Chatterji, A. (2011). Bio-prospecting of a few brown seaweeds for their cytotoxic and antioxidant activities. Evidence-based complementary and alternative medicine, 2011.

 

 

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