Water Requirements of Microorganisms

Microorganisms grow only in aqueous solution. All the microorganisms require water, although some need more than others.

Water is a vital chemical constituent of living cells and it provides an environment for those organisms that live in water.

It is generally accepted that the water requirements of microorganisms should be described in terms of the water activity (Aw) in the environment.

The term is applied to all food, the ordinary fresh type food having an water activity of about 0.99-0.96 at ambient temperature.

Every microorganisms has limiting water activity values below which it will not grow, form spores, or produce toxic metabolites.

Low water activities, which limit the growth of microorganisms in foods, may be brought about the addition of salt or sugar, as well as removal of water by drying.

Solutes (sugar, salts etc.) dissolved in water have an affinity for water and this is therefore unavailable to microorganisms.

Therefore the more dissolved salts, the less likely it is that bacteria will survive.

Under such conditions, the remaining water has been tied up by chemical compounds added top of concentrated in the food or bound to some food component such as protein.
Water Requirements of Microorganisms