‘Carbohydrate’ literally means ‘carbon hydrate,’ which is reflected in the basic building block unit of simple carbohydrates, i.e. (CH2O)n. Carbohydrates make up the majority of organic mass on earth having the biologically important roles of energy storage (e.g. plant starch, animal glycogen), energy transmission (e.g. ATP, many metabolic intermediates), structural components (e.g. plant cellulose, arthropod chitin), and intra- and extracellular communication (e.g. egg-sperm binding, immune system recognition).
Critical for the food industry, carbohydrates serve as the primary nutritive energy sources from foods like grains, fruits and vegetables, as well as being important ingredients for many formulated or processed foods. Carbohydrates are used to sweeten, gel, emulsify, encapsulate or bind flavours, can be altered to produce colour and flavour via various browning reactions, and are used to control humidity and water activity.
Structures The basic unit of a carbohydrate is a monosaccharide; 2 monosaccharides bound together are called a disaccharide; 3 are called a trisaccharide, 2–10 monosaccharides in a chain are termed an oligosaccharide, and 10 or more are termed a polysaccharide. The simplest food-related carbohydrates, monosaccharides, are glucose, mannose, galactose and fructose. Carbohydrate structures contain several hydroxyl groups (–OH) per molecule, a structural feature that imparts a high capacity for hydrogen bonding, making them very hydrophilic.
This property allows them to serve as a means of moisture control in foods. The ability of a substance to bind water is termed humectancy, one of the most important properties of carbohydrates in foods. Maltose and lactose (discussed later) have relatively low humectancies; therefore, they allow for sweetness while resisting adsorption of environmental moisture. Hygroscopic (water absorbing) sugars like corn syrup and invert sugar (hydrolysed table sugar) help prevent water loss, e.g. in baked goods. In addition to the presence of hydroxyl groups, humectancy is also dependent on the overall structures of carbohydrates, e.g. fructose binds more water than glucose.