Functional and chemical properties of fats

Lesson objectives By the end of this lesson students should be able to: explain the term shortening explain the term aeration explain the term plasticity explain the term emulsification.

Function of different fats and oils Function and properties of fats Explanation Shortening The process in which fat coats flour particles, preventing absorption of water (to form gluten) resulting in a crumbly texture. Fat coats the flour particles, preventing the absorption of water, resulting in a crumbly mixture. The fat: gives the flour particles a waterproof coating. prevents the flour from absorbing water reduces the development of gluten Gluten would make the dough stretchy and elastic, but because gluten development is reduced a crumbly texture is the result. Aeration  When air is trapped in a mixture   Air needs to be added to a cake mixture in order to give a springy and well risen texture When the fat and sugar are creamed together with a whisk or wooden spoon, they enclose tiny bubbles of air. The tiny bubbles of air make a stable foam which can be baked to give the springy texture.

Function of different fats and oils Function and properties of fats Explanation Plasticity The ability of a solid fat to soften or melt over a range of temperatures   Plasticity describes the ability of a solid fat to soften over a range of temperatures. Plasticity affects the spreading, creaming and shortening ability of the fat. Fat chosen for shortening must have good plasticity – needs to spread over a large area of flour and coat it with a film of oil. Too hard – poor spreading. Liquid (oil) - will clump rather than make a coating. Emulsification When two unmixable/ immiscible liquids are forced together   An emulsion is a special type of liquid where tiny droplets of one liquid, like oil, spreads throughout the other, such as water. Emulsions should last and not separate out – sometimes if allowed to stand for some time oil or water will separate out from mixture Formation of an emulsion depends on presence of an emulsifier – a substance that will allow two immiscible/unmixable substances to be held together.

Two types of emulsion There are two types of emulsions: An oil-in-water emulsion. This forms when the amount of water is more than the amount of oil. Tiny oil droplets are spread throughout the water. Milk is a good example of this type of emulsion, it contains about 4% fat and 96% water. The small droplets of fat are spread throughout the milk. A water-in-oil emulsion. This forms when the amount of oil or fat is more than the amount of water. Tiny water droplets of water are spread through the fat or oil. Butter and fat spreads are water-in-oil emulsions.

Emulsifiers A substance that will allow two immiscible/unmixable substances to be held together. How does it work? An emulsifier consists of two parts: water-loving part which we describe as hydrophilic water-hating part which we describe as hydrophobic One part of the emulsifier attracts the water and one part attracts the oil This combination holds the oil and water together Emulsifiers lowers the surface tension between the two liquids so that they can combine to form a stable emulsion. Emulsifiers are very important in food production. There are numerous artificial emulsifiers used in food processing industry. Food examples: ice cream, mayonnaise, salad dressing. Lecithin is a natural emulsifier found in egg yolk – normally used in making mayonnaise