Some fruits, seeds and nuts are rich in oils that can be extracted.The plant material is crushed and the oil removed by pressing or insome cases by distillation. Water and other impurities are removed.
Vegetable oils are important foods and fuels as they provide a lotof energy. They also provide us with nutrients.Vegetable oils have higher boiling points than water and so can beused to cook foods at higher temperatures than by boiling. Thisproduces quicker cooking and different flavours but increases theenergy that the food releases when it is eaten.
Oils do not dissolve inwater.They can be used toproduce emulsions.Emulsions are thickerthan oil or water andhave many uses thatdepend on their specialproperties. They providebetter texture, coatingability and appearance,for example in saladdressings, ice creams,cosmetics (such as facecreams, body lotions andlipsticks) and paints.
Emulsifiers have hydrophilic heads and hydrophobic tails, whichare charged.The tails ‘hate’ water but the heads ‘love’ it. They stop the oil andwater in an emulsion separating out into layers.The tails dissolve in oil making tiny droplets. The surface of eachdroplet is made up of the heads – the heads are charged and sowill be repelled by other droplets.In this way they keep the droplets apart and stop them forminginto two layers.
Vegetable oils that are unsaturated contain doublecarbon–carbon bonds (C=C). These can be detected byreacting with bromine water. The coloured bromine waterwill decolourise if the oils are unsaturated.
Vegetable oils that are unsaturated can be hardened by reacting them with hydrogen in the presence of a nickel catalyst at about 60 °C. Hydrogen adds to the carbon–carbon double bonds.The hydrogenated oils have higher melting points so they are solidsat room temperature, making them useful as spreads and in cakesand pastries. This process is known as hardening.