Functions of food
Carbohydrate in food
Carbohydrate covers a wide range of natural compounds, such as starches and sugars.
The term carbohydrate covers a wide range of natural compounds including:
- starch;
- sugar;
- fibre or non starch polysaccharides (NSP).
Dextrinistaion
This is due to a reaction involving protein and a reducing sugar. These polymerise to form complex brown coloured compounds called dextrins. These compounds contribute to the colour and flavour of many foods such as toast, bread and croissants. This is known as non-enzymatic browning (Maillard reaction).
Parts of amino acid and sugar molecules in food combine, when heated, to form brown compounds which change its colour, odour and flavour.
Caramelisation
When sucrose (sugar) is heated above its melting point it undergoes a physical change to produce caramel. This happens more readily without water, however syrups will caramelise with rapid heating. This process is used extensively in the production of confectionary. Overheating will cause the substance to become bitter and dark.
Gelatinisation
When starch is mixed with water and heated, the starch granules swell and eventually rupture, absorbing liquid which thickens the mixture.
On cooling, if enough starch is used, a gel forms. This process is used in the production of blancmange.
Flavouring
Sugar, e.g. sucrose, may be used to flavour many products such as drinks, cakes, tomato sauce and confectionary. It supplies sweetness and mouth feel.
Preservative
Sugar in high concentrations prevents the growth of micro-organism.
It is used extensively in the production of jam, marmalade and some canned fruit. Sugar is an important ingredient in determining the shelf-life of a product.
Gelation
Some fruits, such as apples and blackcurrants, are rich sources of pectin. Pectin is used as a gelling agent in the production of jam.
Protein in food
Protein is made up of chains of small units called amino acids.
There are around 20 different amino acids commonly found in plant and animal proteins.
The protein quality and function varies with the different combination of amino acids.
Protein performs different functions in food products depending on their physical shape and chemical structure. When the bonds between amino acids are altered, e.g. by heat or pH, the protein will change.
Denaturation
This is where the protein structure unfolds due to heat, salts, pH, and mechanical action, e.g. meringue. This change is partially reversible.
Coagulation
This follows denaturation when proteins unfold from their coiled state and form a solid network, or set, e.g. a fried egg. This change is irreversible.
Gluten formation
This is where two proteins in wheat flour form gluten when mixed with water. Gluten is strong, elastic and forms a 3D network in dough e.g. bread.
Gelation
Gelatine is a protein which is extracted from collagen, present in connective tissue in meat. When it is mixed with warm water the gelatine protein molecules start to unwind. Although on cooling a stable network is formed, trapping the liquid. Gelation is reversible.
Fat is made up of fatty acids and glycerol. Fat is often described as saturated or unsaturated, depending on the proportions of the different types of fatty acids it contains.
Fat which is liquid at room temperature is called oil. When fat absorbs oxygen, they spoil and become rancid.
Shortening
Fats coat the flour particles and prevent them from absorbing water. This reduces the formation of gluten development, which would cause the dough to become elastic.
Fats such as pure vegetable fats or lard are suitable for shortening because of their low water content. There are distinctive colours associated with the type of fat used. Margarine produces a golden colour and lard produces a pale yellow. A compromise is sometimes reached by using a combination of the two.
Plasticity
Fat does not melt at fixed temperatures, but over a range. This property is called plasticity. It gives all fats unique character.
The plasticity is due to the mixture of fatty acids, each with its own melting point. Some products are formulated with fats with lower melting points so they can spread when taken out straight from the fridge, e.g. margarine, or melt on the tongue, e.g. chocolate.
Other fats have a higher melting point and are used for cooking.
Aeration
Products such as creamed cakes need air incorporated into the mixture in order to give a well risen texture.
This is achieved by creaming a fat, such as butter or margarine, with caster sugar.
Small bubbles of air are incorporated and form a stable foam.
Flakiness
Flaky and puff pastry use fat to help separate layers of gluten and starch formed in the dough. The fat melts during cooking, leaving minute layers.
The liquid present produces steam which evaporates and causes the layers to rise. The fat prevents the layers sticking together.
Retention of moisture
Some fats can help retain a bakery product’s moisture and increase its shelf-life. They may also be used to baste food being cooked by dry heat.
Glaze
Placed on hot vegetables, some fats, e.g. butter or margarine, give glossy appearance.
Fats also add shine to sauces.
Sensory attributes
All fats and oils have unique flavours and odours. Some are more suited for particular purposes than others, e.g. olive oil for salad dressing (for flavour) and lard for pastry (due to its blandness).
They can also contribute to the texture of the food, for example increasing succulence.
The information provided is provided under the Open Government Licence. Terms can be found at: This resource was developed for the DfE Teach Food Technology programme.