Characters of naturally present fatty acids They are usually monocarboxylic acids, R-COOH. The number of carbon atoms is even (4-28). Hydrocarbon chain is not straight but zigzag. They are either saturated or unsaturated (up to 6 double bonds). Naturally present fatty acids are cis non-conjugated. The main functional group is COOH, sometimes fatty acids contain additional functional group other than COOH e.g. OH in hydroxy acids.

Nomenclature and abbreviation of fatty acids The name of fatty acid is derived from the number of carbon atoms. Number + noic (saturated fatty acids). Number + enoic (unsaturated fatty acids with one double bond). Number + dienoic (unsaturated fatty acids with two double bonds). Number + trienoic (unsaturated fatty acids with three double bonds).

Nomenclature and abbreviation of fatty acids Name IUPAC name Abbreviation Stearic acid octadecanoic C18:0 Oleic acid octadecaenoic C18:1C9 Linoleic acid octadecadienoic C18:2C9,12 linolenic acid octadecatrienoic C18:3C9,12,15 12-hydroxyoleic acid (Ricinoleic acid) 12-hydroxy- octadecaenoic C18:1C9 , 12-OH

Common fatty acids I. Saturated Fatty Acids (General Formula : CnH2nO2) Number of carbon Name   Formula Occurance C4:0 Tetranoic Butyric C3H7COOH Butter fat C6:0 Hexanoie Caproic C5H11COOH Butter fat & coconut C8:0 Octanoic Caprylic C7H15COOH C10:0 Decanoic Capric C9H19COOH Cl2:0 Dodecanoic lauric C11H23COOH Palm oil Cl4:0 Tetradecanoic myristic C13H27COOH Palm oil, nutmeg & butter Cl6:0 Hexadecanoic palmitic C15H31COOH Palm oil, c.s.o, olive oil & butter fat Cl8:0 Octadecanoic stearic C17H35COOH milk & animal fats. C20:0 Eicosanoic Arachidic C19H39COOH Arachis oil.

Common fatty acids II- Unsaturated fatty acids [General formula: CnH2n-xO2 (x = d.b x 2)] Number of carbon Name Formula Occurance C18:1C9 Octadecaenoic Oleic C17H33COOH Most oils C18:2c9,12 Octadecadienoic Linoleic C17H31COOH Cotton seed oil & sesame oil C18:3c9,12, 15 Octadecatrienoic Linolenic C17H29COOH Drying oils, e.g. linseed oil

Cyclic Fatty Acids:- Fatty acids containing a carbocyclic unit are most commonly cyclopropene or cyclopentene compounds. The most known cyclopropenyl fatty acids are malvalic and sterculic which are present in high levels in sterculia oils and at lower levels in cottonseed oil. The most common Cyclopentenyl fatty Acids are hydnocarpic acid (16:1), chaulmoogric acid (18:1), and gorlic acid (18:2) which are present in Chaulmoogra oil.

Hydroxy Fatty acids :- These contain hydroxyl groups in their hydrocarbon chains. 12-hydroxyoleic acid or ricinoleic acid, present in castor oil. Essential fatty acids:- They are required for maintenance of normal growth, reproduction and skin permeability. They cannot be synthesized by the cell of the body and must be obtained from external sources, e.g linoleic, linolenic acid.

Physical Examination of oils & fats Melting point The melting point of fat is determined by heating. The fat starts to melt (incipient fusion) & finally become liquid (complete fusion). The difference between incipient and complete fusion is characteristic for individual lipid. Factors affecting melting point 1. The proportion of saturated to unsaturated fatty acids. Saturated fatty acids have a higher melting point. 2. The length of the fatty acid chains. The longer the fatty acid chains, the higher the melting point.

Physical Examination of oils & fats Melting point 3. The geometry of carbon double bonds. Trans fatty acids melt at higher temperatures than cis configuration.  4. The position of the double bonds. The melting point (not greatly) depends on where the double bond is located on the chain.

Physical Examination of oils & fats Titer Test The titer of an oil or fat is the solidifying point of the mixed fatty acid. The titer temperature is characteristic for individual lipid and for assessing the hardness. The lipid is saponified by alcoholic KOH then acidified by HCl to liberate the free F.A. The melted fatty acids are allowed to cool. After the solid begins to separate, the temp rises to certain extent due to the latent heat liberated during solidification. The highest temperature is taken as the titer value.

Physical Examination of oils & fats Maumene test (thermal test) It depends on recording rise in temperature on addition of 1 ml Br2 to 10 ml 10% solution of oil in chloroform (interaction with double bonds). Thermal test gives indication about degree of unsaturation of lipid. Determination of water The moisture content is determined by Karl-Fischer reagent. The reagent consists of I2 + SO2 + anhydrous methanol + anhydrous pyridine. Determination of water content by evaporation is not accurate due to loss of some volatile substances.

Physical Examination of oils & fats Specific gravity Specific gravity (at 25oC) = weight of certain volume of oil weight of the same volume of water The sp. gravity of oils & fats is always less than one. It’s increased by hydrogenation & rancidity due to saturation of the double bonds, in the fatty acids of the oils. It’s measured by pycnometer or westphal balance. Pycnometer Westphal balance

Physical Examination of oils & fats Refractive index (R.I.) Refractive index (at 25oC) = sine the angle of incident light sine the angle of refraction light There are two types of refractometers which are, Abbe refractometer (which reads the true refractive index directly) and Butyro (Bu) refractometer (Which reads arbitrary refractive index). R.I increases with the increase in length of hydrocarbon chain & the number of double bonds.

Physical Examination of oils & fats Viscosity Viscosity is the resistance due to friction between particles. It can be measured by the use of viscometer. Color The color of oil can be measured using lovibond tintometer or the optical density at specified max using spectrophotometer. Color is due to Carotenoids