Simple lipids: Waxes

Lipids are heterogeneous compounds related to fatty acids. They are insoluble in water. Lipids are divided into:
*Saponifiable lipids - contain esters, which can undergo saponification
*Nonsaponifiable lipids - — do not contain ester groups, and cannot be saponified

Saponifiable lipids can also be divided into groups:
*Simple lipids — contain two types of components (a fatty acid and an alcohol)
*Complex lipids — contain more than two components (fatty acids, an alcohol, and other components)

The main simple lipids are triglycerides (also known as triacylglycerols), steryl esters, and wax esters.

Waxes are simple lipids. Structurally, they are considered as esters of long-chain (C14-C36) saturated and unsaturated fatty acids with long-chain (C16-C30) alcohols.

Waxes are insoluble in water, and not as easily hydrolyzed as fats and oils. They are solid at room temperature. The most important waxes in human body are cholesterol esters, which are present in blood and other tissues. They often occur in nature as protective coatings on feathers, fur, skin, leaves, and fruits.

The leaves of plants like rhododendrons, poison ivy and several tropical plants are shiny in appearance due to wax coating on them. This prevents excess evaporation of water and provides protection from the parasites.

Sebum, secreted by the sebaceous glands of the skin, contains waxes that help to keep skin soft and prevent dehydration.

Wax esters may accumulate in considerable amounts in some biological tissues and this class comprises the main constituent of beeswax and jojoba oil.
Simple lipids: Waxes

Steroids: Derived lipids

Lipids are biological molecules that are insoluble in water but soluble in nonpolar solvents. Lipids are widely distributed in nature and present in both plants and animals. There are four main groups of lipids include:
*Fatty acids (saturated and unsaturated)
*Glycerides (glycerol-containing lipids)
*Nonglyceride lipids (sphingolipids, steroids, waxes)
*Complex lipids (lipoproteins, glycolipids)

Steroids are classified as lipids because they are soluble in nonpolar solvents, but they are nonsaponifiable because the components are not held together by ester linkages.

Some common steroids are:
*Cholesterol, ergosterol: present in plants and yeast, a precursor of vitamin D
*Coprosterol: occurs in feces, derived in the intestine by bacterial action on dietary cholesterol
*Lanosterol: It is a major constituent of wool fat and is also present in minor quantities in liver and yeast
*Terpenes: Among the non-saponifiable lipids found in plants

Cholesterol is the most abundant steroid in the body. It is an essential component of cell membranes, and is a precursor for other steroids, such as the bile salts, sex hormones, vitamin D, and the adrenocorticoid hormones.
Steroids: Derived lipids

Lipids in seafood

Lipids are known to be the building blocks of the fats or fatty substances found in animals and plants. They are microscopic layered spheres of oil which, in animals are composed mainly of fats and oils, waxes, phospholipids, steroids (like cholesterol), and some other related compounds.

The amount of lipids and fatty acid composition in seafood is known to be influenced by various factors in different species or within a species, such as geographical region, season, feeding habits and diet, age, sex, spawning period etc.

Seafood lipids encompass important healthy nutrients, such as n-3 polyunsaturated fatty acids (n-3 PUFAs), which may have a significant effect on human cardiovascular health and needs to be supplied by the human diet.

Among these fatty acids, n-3 PUFAs represent a large share. Particularly, eicosapentaenoic acid (EPA; 20:5 n-3) and docosahexaenoic acid (DHA; 22:6 n-3) are the most abundant n-3 PUFA present in seafood.

Fish consumption satisfies nutritional requirements for essential n-3 fatty acids, primarily eicosapentaenoic and docosahexaenoic acids, which are two long chain polyunsaturated fatty acids mainly present in fish.

DHA is mainly found in the brain and the retina, and it plays a key role for the development and maintenance of the visual and cognitive systems.

DHA is essential for normal fetal brain and cognitive development as the formation of neuron synapses in the brain depends strongly on the integration of this fatty acid into growing neurons. Meanwhile, EPA serves as a precursor of eicosanoids which are hormonelike substances such as prostaglandins, thromboxanes and leucotriens.

Consumption of large amounts of n-3 PUFA exerts a positive effect on a wide array of cardiovascular health concerns ranging from hypertension and atherosclerosis to myocardial infarction and stroke. In fact, animal studies indicate that n-3 PUFAs play a bioactive cardiovascular protective role.
Lipids in seafood

Fatty acids

Fats, oils and lipids consist of a large number of organic compounds, including fatty acids (FA), monoacylglycerols (MG), diacylglycerols (DG), triacylglycerols (TG), phospholipids (PL), eicosanoids, resolvins, docosanoids, sterols, sterol esters, carotenoids, vitamins A and E, fatty alcohols, hydrocarbons and wax esters. Classically, lipids were defined as substances that are soluble in organic solvents.

Fatty acids, both free and as part of complex lipids, play a number of key roles in metabolism – major metabolic fuel (storage and transport of energy), as essential components of all membranes, and as gene regulators.

In addition, dietary lipids provide polyunsaturated fatty acids (PUFAs) that are precursors of powerful locally acting metabolites, i.e. the eicosanoids. As part of complex lipids, fatty acids are also important for thermal and electrical insulation, and for mechanical protection.

Most of fatty acids are obtained form the hydrolysis of hard animal fats (tallow), coconut, palm kernel and soybean oils and from the fractional distillation of crude tall oil. Over the years, the production of edible oil fats and oils has soared, with vegetable sources now dominating the filed formally held by butter and lard.

The most common fats (solid) or oils (liquid) are glycerolipids, which are essentially composed of triacylglycerols. The triacylglycerols are accompanied by minor amounts of phospholipids, monoacylglycerols, diacylglycerols and sterols/sterol esters. Fatty acids constitute the main components of these lipid entities and are required in human nutrition as a source of energy, and for metabolic and structural activities.

Fatty acids are carbon chains with a methyl group at one end of the molecule (designated omega, ω) and a carboxyl group at the other end. The carbon atom next to the carboxyl group is called the α carbon, and the subsequent one the β carbon.

Fatty acids are classified according to the presence and number of double bonds in their carbon chain:

Saturated fatty acids
Saturated fatty acids are ‘filled’ (saturated) with hydrogen. Most saturated fatty acids are straight hydrocarbon chains with an even number of carbon atoms. The most common fatty acids contain 12–22 carbon atoms.

Unsaturated fatty acids
Monounsaturated fatty acids have one carbon–carbon double bond, which can occur in different positions. The most common monoenes have a chain length of 16–22 and a double bond with the cis configuration. This means that the hydrogen atoms on either side of the double bond are oriented in the same direction.

Physically, most of the fatty acids are liquid at room temperature. The different properties are to a large extend related to saturation or unsaturation presence. Generally, solid fats are indicated by a dominance of saturated fatty acids and liquid oils are evidence of a high level of unsaturated fatty acids.
Fatty acids