10.4 Fats and Oils

The solid or semisolid triglycerides at room temperature are called fats, while the liquid is called oil (Figure 3). Fats are generally obtained from animals, while oils come from plant products. In fats, saturated fatty acid is usually involved in the formation of ester with glycerol, whereas in oils, unsaturated fatty acid is involved. In case of fats, the saturated fatty acid chain can pack closely together causing them to be solids at room temperature. In case of oil, the unsaturated fatty acid chain can not pack tightly together, and therefore, that leads to usually have low melting points.

Figure 3

Polyunsaturated fats and oils are prone to undergo oxidation by O₂ via radical reaction. The allylic H is the one that is easily removed because the resulting radical is resonance stabilized by the p bonds. The oxidation reaction is responsible for the unpleasant taste and smell associated with sour milk and rancid butter.