![]() ![]() Water activity is used in many cases as a critical control point for Hazard Analysis and Critical Control Points (HACCP) programs. Food formulators use water activity to predict how much moisture migration affects their product. If raisins of a higher water activity are packaged with bran flakes of a lower water activity, the water from the raisins migrates to the bran flakes over time, making the raisins hard and the bran flakes soggy. Water activity values can also help limit moisture migration within a food product made with different ingredients. If a product is kept below a certain water activity, then mold growth is inhibited. Water activity is an important characteristic for food product design and food safety.įood designers use water activity to formulate shelf-stable food. Lower a w substances tend to support fewer microorganisms since these get desiccated by the water migration. ![]() If salami ( a w ≈ 0.87) is exposed to dry air ( a w ≈ 0.5), the salami dries out, which could preserve it or spoil it. For example, if honey ( a w ≈ 0.6) is exposed to humid air ( a w ≈ 0.7), the honey absorbs water from the air. Water migrates from areas of high a w to areas of low a w. As temperature increases, a w typically increases, except in some products with crystalline salt or sugar. Water activity is the thermodynamic activity of water as solvent and the relative humidity of the surrounding air after equilibration. Using this particular definition, pure distilled water has a water activity of exactly one. In the field of food science, the standard state is most often defined as pure water at the same temperature. Water activity ( a w) is the partial vapor pressure of water in a solution divided by the standard state partial vapor pressure of water. For a more general discussion, see thermodynamic activity. ![]()
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