Why measure water activity?
Water activity is defined as the active part or free water of the moisture content of a substance. It affects the physical, mechanical, chemical, and microbiological properties of materials, which include fluidity, cohesion, cohesion, and static phenomena. Food shelf life, color, taste, vitamins, ingredients, aroma stability; mold production and microbial growth characteristics are directly affected by the water activity value. The table on the left shows the minimum water activity required for the growth of some microorganisms. The control of water activity is very important for the shelf life of the product.
If we can measure the activity of water in food, we can predict which microorganism is the potential cause of food breakage and can be detected. Let us consider a cake with a water activity value of 0.81, which has a shelf life of 24 days at 21°C. If the water activity increases to 0.85, these indicators will be reduced to 21 °C for 12 days. This shows that the water activity value determines the microbial growth rate.
Similarly, water activity is also very important for the pharmaceutical industry. The data it provides expresses the following information: the cohesiveness of the tablets, the cohesive power of the powder, the adhesiveness of the coating, and so on.
Water activity and microbial growth
Water activity microorganism
1.00 - 0.91 Most bacteria
0.91 - 0.87 Most yeasts
0.87 - 0.80 Most molds
0.80 - 0.75 most halophilic bacteria
0.75 - 0.65 dry mold
0.65 - 0.60 osmotic pressure resistant yeast
What is water activity?
Water activity is the relative humidity when the hygroscopic substance is in equilibrium with the surrounding space in a small closed container, expressed as 0...1.0 aw. Water activity measurement is mainly used in the food industry and is often used to test the shelf life and quality of the product.
What is equilibrium relative humidity (ERH)?
The equilibrium relative humidity (ERH) refers to the relative humidity when the moisture-absorbing substance and the ambient water vapor exchange reach equilibrium, and is represented by 0...100% RH. Balanced relative humidity is typically used in paper and pharmaceutical applications. The same applies to any moisture-sensitive product.
Water activity and EHR?
Water activity refers to the state in which water exists in a food product, that is, the degree of binding or freeness of the water and the food. The higher the degree of binding, the lower the water activity and the lower the degree of binding, the higher the water activity. The equilibrium relative humidity (ERH) refers to the state of the air around the food. In particular, ROTRONIC products provide users with two units of water activity (aw) and relative humidity (%RH).
What is the moisture content?
Moisture content refers to the percentage of water in solid matter that makes up the total mass.
Relationship between water activity and moisture content?
The higher the moisture content of the food, the greater the water activity; but there is no simple and straightforward relationship between the two. At a constant temperature, the moisture content (%) of the food is plotted against the water activity (Aw) to obtain the moisture sorption isotherms MSI (Moisture Sorption isotherms). As shown in the right figure, the moisture isotherm adsorption line is generally an S-shaped curve. The temperature is fixed. For the same material, this graph is unique and the relationship between the two is corresponding. However, in fact, many natural ingredients and foods may not have the same chemical composition and chemical properties. If you are concerned about the proportion of water, measure the moisture. If you are concerned about the adsorption of water on the substance and its ability to exchange with the outside world, measure the water activity. Our water-active equipment is easy to use, whether on site or in the laboratory.
Why measure water activity?
Water activity is an important parameter in the pharmaceutical and food industry. It refers to the amount of free water in the product and is the basic data for the growth of enzymes and microorganisms.
Water in products, such as food, is limited to different ingredients such as protein, salt, and sugar. These chemically bound waters do not affect the microorganisms. The more moisture binds, the less water vapour it can evaporate. Therefore, more water in the product does not mean that the partial pressure of water vapour on the surface will be high. The equilibrium relative humidity will be large and the microorganisms will be more active.
Water activity has a great influence on the stability of the product (antimicrobial, aroma retention), and has an important influence on the agglomeration of powder, stability of chemicals, and physical properties such as paper size.
Instruments for detecting water activity are generally imported, and the instrument for detecting moisture content is better for Shenzhen Guanya Rapid Moisture Analyzer.
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