###### Abstract  
Seaweeds are becoming a viable source of biologically active composites with a hopeful application as mutraceuticalicals, functional food components, and medicinal agents. In the present study, the antioxidant capacity and biochemical compositions of four seaweeds; _Polycladia indica_ and _Turbinaria ornata_ (Phaeophyceae) and _Laurencia obtusa_ and _Sarconema scinaoides_ (Rhodophyceae), were estimated. The results indicated that _T. ornata_ showed the maximum value of total phenolic compound (TPC), flavonoid content, \(\beta\)-carotene, carbohydrate and has maximum percentage of DPPH radical scavenging capacity, total antioxidant capacity (TAC), and total reducing capacity (TRC) (72.48%, 15.02%, and 53.24% inhibition, respectively), while the highest contents of ascorbic acid, lipid, calcium, and zinc were observed in _L. obtusa. P. indica_ showed the highest protein contents, dietary fibers, sodium, potassium, magnesium, and total amino acids. Glutamic, aspartic, proline, and methionine were the most frequent amino acids in the four selected seaweeds. Brown seaweeds (_T. ornata_ and _P. indica_) attained the highest percent of the total polyunsaturated (u\(\delta\)6 and u\(\delta\)3) essential fatty acids. The biochemical content of these seaweed species, as well as their antioxidant properties, make them interesting candidates for nutritional, pharmacological, and therapeutic applications. seaweeds; biochemical composition; the total antioxidant capacity; fatty acids +
Footnote †: journal: Medical Engineering  
1 Botany and Microbiology Department, Faculty of Science, South Valley University, Qena 83523, Egypt; [EMAIL_ADDRESS]  
2 Biological Sciences Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jedda 21589, Saudi Arabia; [EMAIL_ADDRESS]  
2 Botany and Microbiology Department, Faculty of Science, South Valley University, Qena 83523, Egypt; [EMAIL_ADDRESS]  
2 Biological Sciences Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jedda 21589, Saudi Arabia; [EMAIL_ADDRESS]  
2 Botanyin the prevention of cardiovascular disease, osteoarthritis, and diabetes [6]. Furthermore, macroalgae contain most macroelements and trace elements required for human nutrition and development [7]. These elements are necessary for biological processes such as growth, reproduction, hormone metabolism, and antioxidant defense. Vitamins found in seaweed are important not only for their biochemical functions and antioxidant activity but also for other health benefits such as lowering blood pressure (vitamin C), preventing cardiovascular disease (\(\beta\)-carotene), and lowering cancer risk (vitamins E, C, and carotenoids) [8]. Antioxidant activity refers to the ability of a molecule compound to suppress or avoid the oxidation of a substrate at low doses [9]. The oxidation process in materials for animal and human use and cosmetic preparations can destroy the product. The use of antioxidants aims to prevent oxidation so that these foods and cosmetics do not cause poisoning or disease [10]. Seaweeds have antioxidant substances that act as an endogenous defense mechanism against oxidative stress caused by extreme environmental conditions [11]. Polyphenols have recently been classified as antioxidant compounds (phenolic acid, flavonoid, and tannins). These compounds have been shown to have strong antioxidant properties as anticancer, antibacterial, antiallergic, antidiabetes, antiagin, anti-inflammatory, and anti-HIV activities [12]. Phenolic and flavonoid compounds were detected in abundance in seaweeds under extreme climatic conditions, suggesting their critical role in chelating metal ions, decreasing radical generation, and strengthening the internal antioxidant system. These functions contribute to the prevention of diseases caused by reactive oxygen species (ROS) [13]. This study aimed to investigate the biochemical compositions of some brown algae (_Polycladia indica_ and _Turbinaria ornata_) and red seaweed (_Sarconema scinaioides_ and _Laurencia obtusa_).