# Phytosterols in Seaweeds: An Overview on Biosynthesis to Biomedical Applications
## 1 Introduction  
Marine macroalgae (or seaweed) hold immense nutritional value and have constituted an important position in Asian diets since time immemorial. Traditionally, seaweeds _viz., Undaria pimattifida_ (wakame), _Cladosibmono kamuranus_ (mozuku), _Laminaria japonica_ (kombu) and _Gelidium crinale_ (tengusa) are consumed as healthy foods in Japan [1]. _Sargassum fussiforme_, in addition to being one of the edible seaweeds consumed in Korea and China, holds an important position in traditional Chinese medicine due to its anti-atherosclerotic activity [2]. In recent times, the demands for seaweed in other parts of the world, such as North and South America, have also increased due to the migration of traditional seaweed consumers. Moreover, France has recently approved the human consumption of seaweed as conditions and vegetables, which further increases the value of seaweed in the global food market. Although seaweed has been consumed since prehistoric times, its commercial utilization in food, cosmetics, and pharmaceutical industries was recognized later [3]. Seaweed extracts are generally rich in natural growth hormones, nutrients, andtrace minerals. Among several other compounds, the nutritional value of seaweed is mainly attributed to the presence of phytosterols. Phytosterols, as the name implies, are defined as fatty compounds produced by plants, and remarkably contribute as the major lipid constituent of biological membrane of plant cells. Although these plant steroids have similar chemical structures like cholesterol, the differentiation in C\({}_{24}\) side chains makes them metabolically and functionally distinct from each other [4]. Like terrestrial plants, seaweeds as well, exhibit the diversified composition of phytosterol contents with a similar profile of health benefits and their prevalence in this phytoplankton is largely influenced by their evolutionary origin [5; 6]. For instance, brown algae (phaeophyta) predominantly contain phytosterols such as toxosterol and brassicasterol, with a small proportion of plant cholesterol and therefore considered a promising source for phytosterols. In contrast, red algae (rhodophyta) contain cholesterol as their principal sterol content, with a minor quantity of phytosterols such as sitosterol, rlocosterol, chalinsterol and desmosterol. On the other hand, green algae (chlorophyta) vary in their types of sterols, such as ergosterol, chondillasterol, \(\beta\)-sitosterol, 28-isofucosterol, cholesterol and porifearosterol, depending on the species [7; 8]. Furthermore, to date, there have been no studies found to demonstrate the obvious negative effects (in terms of toxicity) of phytosterols on humans. Accordingly, international agencies such as the Food and Drug Administration (FDA) and the European Union Scientific Committee (EUSC) have already approved phytosterols as safe to use [9]. Despite the myriad of research interest in phytosterols, there has been a lacuna in an up-to-date literature survey elucidating their biosynthesis, pharmacological effects and other biomedical applications. Therefore, the goal of this review is to provide an overview of the biosynthesis, extraction, and characterization of phytosterols in seaweed, as well as of their biological properties with biomedical applications, for effective seaweed utilization in the food and pharmaceutical industries.