In proximate analysis everyone reports the alcohol solubles in a sample. This fraction contains almost all water insoluble compounds- named lipids. Let me introduce lipids with an anecdote.
Once in one of my biochemistry classes, after finishing Carbohydrates and Proteins which are water soluble components (and thus useful in foods), I started with water insoluble topic, lipids. In the middle of my lecture, one smart boy interrupted me and asked. “Sir, if they are not water soluble why should we need (to study) them?” I fumbled for a moment but regained my composure shortly and said “My dear friend, if we do not have lipids, while bathing you pour water on your head, you will be flowing down through drainage”. Well that explained the importance of lipids around us. It is the lipids that define us, our cells, tissues, organs etc or our shape !!!!
(I am sure that, after a bath, all of you will be thanking your lipids!!)
Lipid is a term defined differently by various workers. But everybody understands lipids as a term denoting all water-insoluble (oil soluble, hydrophobic) compounds of living organisms.Certain biochemists include only fats (oils) and fat-derived compounds in their definition of lipids and exclude terpenoids like steroids. But off late, all terpenoids also are included in this group. In all my books I followed the classification of T.Robinson (1975) in which lipids are classified to 1. Saponifiable lipids (forming soap with alkalies) and 2. Non saponifiable lipids (isoprenoids- do not form soaps with alkalies). This classification gets support from biosynthsynthetic pathways in that saponifiable lipids are all formed by “Acetyl CoA pathway” and Isoprenoids by “Mevalonic acid pathway”.
1.Saponifiable lipids: Acyl lipids
All saponifiable lipids contain fatty acids in common and are esters of fatty acids with an alcohol. When the fatty acids combine with glycerol we get fats and oils. But there are many fats in which phosphate groups (Phospholipids) or sugars (glycolipids) are also added.
A. Fats and oils.(Triacyl glycerols, wrongly named triglycerides). These are the esters in which 3 hydroxyl groups of glycerol get esterified with fatty acids. The main difference between fats and oils is their physical nature in that fats are solids at room temperature and oils are liquids at the same conditions. Fats becomes oils on heating and oils become fats on freezing. Another point of difference is that fats contain mainly saturated fatty acids and oils contain unsaturated fatty acids. Oils on hydrogenation become fats and such fats are known as margarines or “vegetable ghee” (eg. Dalda vanaspati). The importance of avoiding saturated saturated fats and the role in heart problems are much discussed. Here we discuss about some uncommon fats/oils
a. Castor oil: The oil of Ricinus communiscontains ricinoleic acid (12-hydroxy oleic acid) as the fatty acid components and the use of castor oil as a purgative is because of this acid.
b. Chaulmoogra oil, This oil obtained from Hydnocarpus wightiana contains cyclopentene fatty acids hydnocarpic and chaulmoogric acids, whichshow strong bactericidal properties towards Micrococcus of leprosy and so are used for the treatment of leprosy.
Glycolipids: Here one of the hydroxyl groups of triacyl glycerols is esterified with an oligosaccharide. These are seen in mitochondrial membranes.
Indian Jalap, Trivert The resin form Operculina turpethum contains three glycosides turpethin (major component), a-turpethin and b-turpethin. They are gluco–gluco–gluco–rhamnosides of 11–hydroxy palmitic acid (Jalapinolic acid), 3,12–dihydroxy pentadecanoic acid (Operculinolic acid). The drug owes its cathartics and hydragogue action to these compounds.
Phospholipids are triacyl glycerols in which one hydroxyl group of glycerol, normally that of a’- position is esterified with a molecule of phosphoric acid. Lecithins and cephalins contain a nitrogenous compound (choline/ethanolamine) linked as an ester with the phisphate group. These are the best organic emulsifiers used in many liquid medicinal preparations like syrups and tonics. Their role in membranes is well known. They are one of the best natural antioxidants.
Waxes, cutins and suberinsalso are lipids of fatty acids with fatty alcohols. Octacosanol is a fatty alcohol present in sugar cane wax and wheat germ oil used for athletic performance, Parkinson’s disease, atherosclerosis and lowering cholesterol.
Source:
“Useful Herbs of Planet Earth” By M. Daniel (2013) Scientific Publishers, Jodhpur/ New Delhi.
Mammen Daniel
