Iodine Number
The iodine number (or iodine value) determines the number of double bonds of the fatty acids present in a fats, oils and waxes. The iodine number measures the degree of unsaturation in the fats, oils and waxes by reacting with the double bonds via an electrophilic addition reaction, and the amount of iodine consumed indicates the number of double bonds present. Thus, higher the iodine value, more unsaturations are present in the fats, oils and waxes. The iodine number is expressed in iodine which is added to 100 grams of the sample. The iodine number is defined as the mass of iodine in grams that is consumed by 100 grams of a chemical substance.
Iodine value helps to classify oils according to the degree of unsaturation into drying oils. Drying oils have iodine value more than 150, semi-drying oils have iodine value between 125 to 150 and non-drying oils have iodine value less than 125. The iodine value of several common oils and fats are given below in table.
| Fat | Iodine value (gI/ 100g) |
|---|---|
| Beef tallow | 42 – 48 |
| Beeswax | 7 – 16 |
| Butter | 25 – 42 |
| Canola oil | 110 – 126 |
| Castor oil | 81 – 91 |
| Dehydrated castor oil | 127 - 140 |
| Cocoa butter | 32 – 40 |
| Coconut oil | 6 – 11 |
| Cod liver oil | 148 – 183 |
| Corn oil | 107 – 128 |
| Cottonseed oil | 100 – 115 |
| Fish oil | 190 – 205 |
| Grape seed oil | 94 – 157 |
| Hazelnut oil | 83 – 90 |
| Jojoba oil | 80 – 85 |
| Kapok seed oil | 86 – 110 |
| Lard | 52 – 68 |
| Linseed oil | 170 – 204 |
| Olive oil | 75 – 94 |
| Oiticica oil | 139 – 185 |
| Palm kernel oil | 14 – 21 |
| Palm oil | 49 – 55 |
| Peanut oil | 82 – 107 |
| Pecan oil | 77 – 106 |
| Pistachio oil | 86 – 98 |
| Poppyseed oil | 140 – 158 |
| Rapeseed oil | 94 – 120 |
| Rice bran oil | 99 – 108 |
| Safflower oil | 135 – 150 |
| Sesame oil | 100 – 120 |
| Sunflower oil | 110 – 145 |
| Soybean oil | 120 – 139 |
| Tung oil | 160 – 175 |
| Walnut oil | 132 – 162 |
| Wheat germ oil | 115 – 128 |
Data Source: wikipedia
Significance of Iodine Value
Iodine number determine the extent of unsaturation in fats, oils, and waxes. Higher number of iodine value indicates a greater number of double bonds, meaning the substance is more unsaturated. Higher degree of unsaturation leads to greater susceptibility to oxidation and rancidity.
The value of iodine number tells about the stability and drying properties of oils. Higher the iodine value, less stable the oil and used as drying oils in paints.
The iodine number explain the quality and suitability of raw materials for food, paint, and varnish. Drying oils (linseed oil) used in paints have high iodine numbers while non-drying oils (olive oil) have low iodine numbers.
Iodine Value (IV) and Stability Correlation
| Iodine Value (IV) | Degree of Unsaturation | Chemical Stability | Susceptibility to Rancidity | Example |
|---|---|---|---|---|
| Low (< 70) | Low (mostly saturated) | High | Low (long shelf life) | Coconut Oil, Butter |
| Medium (70–125) | Moderate (monounsaturated) | Moderate | Moderate | Olive Oil, Peanut Oil |
| High (> 125) | High (polyunsaturated) | Low | High (short shelf life, requires antioxidants) | Linseed Oil, Cod Liver Oil |
This correlation demonstrates that the Iodine Value is a critical indicator of oil stability and its industrial suitability.