3.3.1. Role of Fatty Acids in Medicine

There is an increasing need to assess new food sources that do not involve overexploitation of terrestrial ecosystems [133]. Seaweeds have a lipid output of 0.61% to 4.15% dry weight (DW) on average. Some seaweed species, on the other hand, can have greater levels since they are a strong source of unsaturated fatty acids. Although seaweed has lower lipid content than marine fish, their abundance in coastal areas makes it a viable source of functional lipid. Recent studies indicated that the levels of total lipid (TL) or omega-polyunsaturated fatty acids in seaweeds vary seasonally, reaching up to 15% TL per DW or more than 40% omega-3 PUFAs per total fatty acids [134]. Brown seaweed lipids, on the other hand, contain up to 5% fucoxanthin. Anti-obesity activities of fucoxanthin have been demonstrated. It also reduces insulin resistance and lowers blood glucose levels significantly. Brown seaweed lipids are found in brown seaweed, according to a study. Excess fat builds up in abdomen white adipose tissue (WAT) is dramatically decreased, or glucose levels are regained to average limits in obesity/diabetes model mice due to presence of fucoxanthin in lipids [135].

On the other hand, the group of lipid bioactive chemicals known as sterols is another appealing lipid bioactive substance found in marine sources. Sterols extracted from macroor microalgae, as well as other marine invertebrates, were researched extensively by [136]. Previously, it was discovered that sterols and several of their derivatives have a key role in decreasing low-density lipoproteins (LDL) cholesterol levels in vivo. Anti-inflammatory and antiaterogenic action are two further bioactivities linked to sterols. Phytosterols (C28 and C29 sterols) are also key precursors of a wide range of chemicals, including vitamins. Ergosterol, for example, is a precursor to vitamin D2 and cortisone [137].

Omega-3 (eicosapentaenoic acid, docosahexanoic acid, stearidonic acid, -linolenic acid) and omega-6 (arachidonic acid, -linoleic acid, -linoleic acid) are the most common polyunsaturated fatty acids (PUFAs) [1]. Essential fatty acids (EFAs) are nutraceuticals that are combined with nutritional supplements or used as part of healthy food [41]. Food and Drug Administration (FDA) declared in 2004 which foods including PUFA omega-3 substances are medicinally essential, as they provide therapeutic properties byregulating blood pressure, membrane fluidity, or blood clotting; (ii) lowering risk of cardiovascular disease, osteoporosis, or diabetes; (iii) correcting brain or nervous system development and function [138]. Marine algae were found to have elevated high levels from PUFAs (α-linolenic acid, γ-linoleic, α-linoleic acid, stearidonic acid, arachidonic acid, and icosapentaenoic acid) [1]. Moreover, a previous study asserted that green seaweeds such as *Ulva pertusa* possess a high concentration of hexadecatetraenoic, oleic, and palmitic acids [139]. Additionally, *Undaria pinnatifida* contains significant levels of eicosapentaenoic acid, docosahexanoic acid, and monounsaturated fatty acids (C12:1 (lauroleic acid), C14:1 (myristoleic acid), C16:1 (palmitoleic acid), C17:1 (cis-10-heptadecenoic acid), and C18:1 (cis-10-hepta (oleic acid) [140].

Upwards of 200 phytosterols (662–2320 mg/g dry weight) were discovered through marine algae. Phytosterol derivatives are abundant in brown algae such as *Laminaria japonica*, *Agarum cribosum*, or *Undaria pinnatifida* (for example, fucosterol, which accounts for 83–97 percent of total phytosterol content) [141,142]. Phospholipids in seaweed contain about 10–20% total lipids which seem to be more resistant to oxidation and contain elevated concentration from FAs such as eicosapentaenoic or docosahexanoic acid [43]. Glycolipids make up more than half of all algal material and are characterized by high levels of n-3 PUFAs (e.g., monogalactosyldiacylglycerides, digalactosyldiacylglycerides or sulfoquinovosyldiacylglycerides) [41]. Carotenoids are a group of lipophilic colorful chemicals found in nature that include lutein, lycopene, canthaxanthin, β-carotene, or astaxanthin [143]. Furthermore, these properties make algal lipids more bioavailable or provide a variety of health benefits to people or animals [109].

## 3.3.2. Role of Fatty Acids in Foods

Microalgae have a high PUFA content. They are fatty acids with many double bonds in the carbon chain and have numerous useful qualities. Microalgae may produce members of the PUFAs ω-6 family, such as linoleic acid (LA), γ-linolenic acid (GLA), and arachidonic acid (ARA), as well as members of the PUFAs ω-6 family, such as α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) [144,145]. Many microalgae manufacture the long chain of -3 PUFAs, with yields exceeding 20% of total lipids. The microalgae most commonly employed for the formation of algal oil rich in ω-3 and biomass are marine members of the Thraustochytriacea and Crythecodiniacea families [146].

Because of their obvious benefits to tissue integrity and health, they are vital ingredients for food additives and feeds. Microalgae such as *Chlorella vulgaris*, *Arthrospira platensis*, *Haematococcus pluvialis*, and *Dunaliella salina* have been identified as safe or permitted as human and animal food additives. *Scenedesmus almeriensis* and *Nannocholoropsis* sp. are two more species that have been investigated but have not yet been commercialized [147].

*Crypthecodinium*, *Schizochytrium*, *Thraustochytrids*, and *Ulkenia* microalgal species are employed in the manufacture important fatty acids [148]. DHA-rich oil derived from *Crypthecodinium cohnii* is commercially accessible and contains 40–50% DHA with no EPA or other longchain PUFAs [149]. Schizochytrium species that synthesize DHA and EPA are currently employed as an adult dietary supplement in food and drinks, health foods, animal feeds, and foodstuffs products such as cheeses, yogurts, spreads and sauces, and breakfast cereals. This microalga's essential fatty acids are used as supplements in diets for pregnant and nursing women, as well as cardiovascular patients [149].
