Introduction to Fats and Oils
Fats and oils are lipid esters made of glycerol and fatty acids, forming the basis of many pharmaceutical excipients, ointment bases, and lipid-based drug delivery systems. This unit covers their chemical reactions and the analytical constants used by the pharma and food industry to characterize and control quality.
Syllabus & Topics
- 1Fatty acids: Classification (saturated vs unsaturated), nomenclature (common and IUPAC).
- 2Reactions of fatty acids: Hydrogenation (hardening of oils), Halogenation (addition to double bonds), oxidation.
- 3Hydrolysis of fats and oils: Saponification with alkali (NaOH → hard soap; KOH → soft soap).
- 4Hydrogenation: Conversion of vegetable oils to vanaspati ghee (partial hydrogenation).
- 5Rancidity of oils: Hydrolytic rancidity (free fatty acids released by lipase), Oxidative rancidity (auto-oxidation of unsaturated fatty acids – PUFA), Ketonic rancidity.
- 6Drying oils: Oils with high unsaturation (high Iodine Value >130) that polymerize on exposure to air (e.g., Linseed oil, Tung oil). Used in varnishes and paints.
- 7Analytical Constants of fats and oils:
- 8Acid Value: mg of KOH required to neutralize free fatty acids in 1g of oil. Indicates rancidity. (Standard: <0.5 for edible oils).
- 9Saponification Value: mg of KOH to saponify 1g of fat completely. Indicates average molecular weight of fatty acids. High SV = short-chain fatty acids.
- 10Ester Value: Ester Value = Saponification Value – Acid Value.
- 11Iodine Value: g of Iodine absorbed by 100g of fat. Indicates degree of unsaturation. High IV = highly unsaturated (Linseed oil ~170-190).
- 12Acetyl Value: mg of KOH needed to saponify acetyl groups after acetylation. Indicates free hydroxyl groups in fat.
- 13Reichert Meissl (RM) Value: mL of 0.1N KOH to neutralize volatile water-soluble fatty acids from 5g of fat. Used to detect adulteration in butter (butter has high RM ~26-28; vanaspati has low RM ~0.5-1)
Learning Objectives
Frequently Asked Questions (FAQs)
Q1. What is Saponification Value and what does it indicate?
Saponification Value (SV) is the number of milligrams of KOH required to completely saponify 1 g of fat or oil.
It indicates the average molecular weight of fatty acids present:
High SV → Short-chain fatty acids (low molecular weight)
Low SV → Long-chain fatty acids (high molecular weight)
Examples:
Coconut oil → ~250
Castor oil → ~180
Q2. What is Rancidity in oils?
Rancidity is the spoilage of fats and oils leading to unpleasant odor and taste. It occurs by:
Hydrolytic rancidity – Lipase enzyme or water breaks ester bonds, releasing free fatty acids (e.g., butyric, caproic acid).
Oxidative rancidity – Auto-oxidation of unsaturated fatty acids forms aldehydes and ketones.
Antioxidants like BHA (Butylated Hydroxyanisole) and BHT (Butylated Hydroxytoluene) help prevent oxidative rancidity.
Q3. What is the significance of Iodine Value?
Iodine Value (IV) is the number of grams of iodine absorbed by 100 g of fat or oil.
It measures the degree of unsaturation (number of double bonds):
High IV → More unsaturation → Good drying oil
Low IV → More saturation
Examples:
Linseed oil (IV ~190) → Drying oil
Olive oil (IV ~80) → Non-drying oil
Coconut oil (IV ~10) → Highly saturated
Q4. What are Drying Oils and how do they “dry”?
Drying oils have high iodine value (IV >130) and are rich in polyunsaturated fatty acids (e.g., linolenic acid).
On exposure to air, they polymerize (cross-link) through oxidation.
This is a chemical reaction, not evaporation, resulting in the formation of a hard, tough film.
They are commonly used in paints and varnishes.
Q5. What is the Reichert–Meissl (RM) Value used for?
Reichert–Meissl (RM) Value is the volume (mL) of 0.1N KOH required to neutralize volatile, water-soluble fatty acids obtained from 5 g of fat.
Pure butter → High RM value (~26–28) due to short-chain fatty acids (butyric, caproic).
Adulterated butter or vanaspati → Very low RM value (~0.5–1).
It is an important analytical test for detecting butter adulteration.