食品质量控制中水分活度重要性检测方案(水活度分析仪)

novasinaThe Art of Precision MeasurementNovasina/ZIC 09.2005 Water activity and the importance in food Water is an important basic element in foods. For a long time， the industry has known howimportant it is to check free water. The water activity (aw) measurement forms the basis ofthis and provides important information about the quality of a product. Finally it providesinformation regarding the possibility of microbiological growth on the surface. Only with thisconclusions can be made about the stability and durability of a sample Definition of water activity Water activity is defined as the current volume and availability of "free"water in a sample andshould not be directly compared with the water content (g water/ g substance). The wateractivity is given as the aw- value and range between 0 (absolute dryness) and 1 (condensedhumidity). Only this component takes an active part in the exchange with the ambienthumidity and can possibly form the ideal medium for microbiological growth on the surfacewhich influences the microbiological stability. The water activity also has an important effecton the chemical reactions in food. The relative humidity is measured in % rH and relates to the aw -value as follows： The influence of water activity in foods The relative equilibrium humidity of a product， which is ascertained through its partialpressure of water vapour on the surface， depends on the following factors： Chemical compound Temperature T●Water contentStorage environment (T/RH) Absolute pressure Packing “Free” water in products is jointly responsible for the growth of undesirable organisms suchas bacteria or fungi， which produce“toxins”or other harmful substances. But alsochemical/biochemical reactions (e.g. the Maillard reaction) increasingly take place andpossibly change the following factors of a product： ·Microbiological stability (growth) ·Chemical stability (see table) ·Content of proteins and vitamins ·Colour， taste and nutritional value ·Stability of the compound and durability ·Storage and packing ·Solubility and texture The variation of oxydation， browning， enzyme activity， The optimisation and stabilisation of the product properties require a partially narrow upperas well as lower aw value margin. The aw- value of a product can be changed by adding ofso called Humectans. Nowadays the measurement of water activity in the food industry isestablished in research， development， quality control and production. Indirect water content determination With the new water activity instrument of Novasina the determination of the water contentvia the so-called“sorption isotherm” is possible. The sorption isotherm shows the relationbetween water content and water activity at a given temperature. With this process， thesample is not destroyed and can correspondingly be stored for future checks. SI， Sorption Isotherm of potatoes Water is an important basic element in foods. For a long time, the industry has known howimportant it is to check free water. The water activity (aw) measurement forms the basis ofthis and provides important information about the quality of a product. Finally it providesinformation regarding the possibility of microbiological growth on the surface. Only with thisconclusions can be made about the stability and durability of a sample