Moisture Vs Water activity in 60 seconds скачать в хорошем качестве

Moisture Vs Water activity in 60 seconds

Water activity is the amount of unbound water present in the sample. In other words part of the water is normally chained to chemical groups in the sample and can not move freely to be used for example by bacteria which would cause food spoilage. Water activity is based on a scale of 0 to 1.0 with pure water having a value of 1.00. It is defined as the vapour pressure of water in a sample divided by the vapour pressure of pure water at the sample temperature. As the chemically bound water can not escape only the free water will exert vapour pressure and therefore this characteristic can be used to determine microbial spoilage, chemical stability, and physical stability. For example in the majority of food samples a water activity of 0.5 will mean the likelihood of microbial growth is very low. Moisture and water activity have a unique relationship for each product. This relationship is referred to as the moisture adsorption isotherm and it must be determined experimentally by measuring water content at several water activity values. Once the isotherm has been generated, it can be used to indirectly determine moisture content based on a water activity measurement or vice versa. Visit us at Better-engineers.com for more our our video magazine.