Carbohydrates

Element composition of carbohydrates.

Element composition of carbohydrates.

Carbon (C) Hydrogen (H) Oxygen (O)

Photosynthesis

The process by which green plants trap sunlight energy and use this energy to chemically convert carbon dioxide and water into glucose and oxygen

Glucose formula

C6H12O6

Classification of carbohydrates

Monosaccharides, Disaccharides, Polysaccharides

Monosaccharides

C6H12O6, simple sugar, hexagonal ring structure, Fructose-Honey Glucose-Fruit Galactose-Milk

Disaccharides

C12H22O11, Two simple sugars join together with the loss of H2O, Sucrose- Table sugar Lactose-Milk Maltose-Barley

Polysaccharides

(C6H10O5)n, N is the number of monosaccharides linked together, Three or more sugar units join together, Branched straight, Pectin-Fruit Glycogen-Meat, Non-Starch; Pectin-Fruit Cellulose-Skins of fruit Gums-Seaweed, plant

Properties of sugar

Sweetness, Solubility, Maillard reaction, Assists aeration, Caramelisation, Crystallisation, Inversion, Hydrolysis

Sweetness

Sweet white crystalline solid with varying degrees of sweetness giving flavour to food, sweetens beverages, cakes, desserts

Maillard reaction

Causes non-enzymic browning of food, Sugar + an amino acid + dry heat = browning of food. Roast potatoes, toast, shortbread biscuits

Assists aeration

Sugar denatures egg protein which allows aeration to occur, whisking an egg with sugar causes egg protein chains to unfold and trap air, heat is generated which begins to set the egg albumin forming a temporary foam. Meringues, sponge cakes

Caramelisation

When dry heat is applied, sugar melts and caramelises, temp range from 104OC to 177OC, if overheated the caramel will carbonise or brown. Crème brûlée, caramel squares

Crystallisation

Occurs when water has dissolved as much sugar as it can and the solution becomes saturated. Crystals form when the mixture cools down. Confectionary, boiled sweets, fudge

Inversion

When sugar reacts with water in the presence of an acid or an enzyme (invertase) it converts disaccharides into monosaccharides. Jam making

Hydrolysis

Disaccharides react with water to produce monosaccharides, Enzymes can speed up the reaction, Hydrolysis is the reverse of the condensation reaction

Properties of starch

Solubility, Flavour, Hydroscopic, Gelatinisation, Dry heat, Dextrinisation, Gel formation

Solubility (S)

Insoluble in cold water

Flavour (S)

Starch lacks flavour

Gelatinisation (S)

When starch is heated in the presence of water, starch grains swell, burst, absorb water and form a sauce (Sol), on cooling the mixture forms a gel. Roux sauce, Lemon curd

Dry heat (S)

With dry heat starch grains burst and absorb fat. Pastry’s, Popcorn

Dextrinisation (S)

Short chains of polysaccharides (dextrins) change starch foods to brown when heated (prodextrins). Toast

Gel formation (S)

The long polysaccharide chains in pectin when heated form a 3D network that traps water, When cooled the mixture forms a gel. Jam making

Chlorophyll

The pigment present in green plants traps the sunlight energy which is then used to convert, water absorbed from the roots and CO2 absorbed at the leaves, into the carbohydrate glucose and oxygen