Food | Standards
The preparation of processed foods is a complex science, which requires an understanding of complex chemical interactions as well as culinary expertise. Shelf life can be extended by dehydration and addition of preservatives, however, these will affect the texture and taste of the food. A careful balance of ingredients and preparation techniques can produce a tasty food with a long shelf life. The interaction of the food and additives with water is an important factor in optimizing food processing. Measurement of the amount of water in the food, how rapidly it adsorbs or loses water, and the effect of water on the interaction of the ensemble of ingredients is key to the control of the process. |
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Water ActivityWater Activity (Aw) is defined as the ratio of the partial vapor pressure of water in a substance to the vapor pressure of pure water at the same temperature (i.e. P/P0). Since high Aw supports the growth of microorganisms, controlling the Aw is important to the shelf life a foods. The “out of the box” water activity of foods can be measured by placing the food in a closed container allowing it to come to equilibrium and measuring the relative humidity in the chamber. In this case Aw = RH/100. The Aquadyne DVS has the capability to measure the relative humidity in a thermostatically controlled chamber. Although the chamber is not hermetically sealed, since it is designed as a dynamic system, it is sufficient to establish equilibrium and determine the water activity. |
Food | Standards
More important than the static water activity is the rate at which a food gains or loses water. Over time, unless hermetically sealed, a food will either gain or lose moisture to achieve equilibrium with its environment. Design of packaging is critical in slowing this exchange of water, but once the package is opened it is desirable for the food to gain or lose water as slowly as possibly. Measuring the rates of water sorption under various humidity conditions can help food designers to optimize the formulations and increase the length of time a food remains fresh after opening. The Aquadyne DVS can control the temperature and relative humidity, while continuously measuring the mass change (due to gain or loss of water) over time. This kinetic information can also be obtained using the VSTAR vacuum-volumetric vapor analyzer. Vacuum-volumetric (manometric) analyzers are typically faster than gravimetric analyzers, since in gravimetric analyzers the water has to compete with the carrier gas to reach the surface and diffuse into the sample. However, gravimetric systems more closely simulate “real world” conditions of food handling and storage.
Relevant Tech Notes:
#44 - Water Vapor Sorption by Milk Powders.
#45 - Kinetics of Water Vapor Sorption by Apple.
Food | Standards
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Food | Standards
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Food | Standards
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