Water activity is a dimensionless quantity used to represent the energy status of the water in a system. It is defined as the vapor pressure of water above a sample divided by that of pure water at the same temperature; therefore, pure distilled water has a water activity of exactly one. It is widely used in food science as a simple, straightforward measure of the dryness of food; foods typically have an optimum water activity at which they have the longest shelf life.

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dbpprop:abstract
  • Water activity is a dimensionless quantity used to represent the energy status of the water in a system. It is defined as the vapor pressure of water above a sample divided by that of pure water at the same temperature; therefore, pure distilled water has a water activity of exactly one. It is widely used in food science as a simple, straightforward measure of the dryness of food; foods typically have an optimum water activity at which they have the longest shelf life. It is also used in the pharmaceutical industry and chemicals for moisture sensitive products. There are several factors that determine the water activity of a substance. Colligative effects of dissolved species (e.g. salt or sugar) interact with water through dipole-dipole attraction, ionic bonds and hydrogen bonds. Capillary effects also influence water activity, because the vapor pressure of water above a curved liquid meniscus is less than that of pure water. Surface interactions, in which water interacts directly with chemical groups on undissolved ingredients, can also affect water activity. In this case the interaction can be through ionic bonds, van der Waals forces, hydrophobic interaction and hydrogen bonds. These factors combine to increase the energy required to cause the water to evaporate, and therefore reduce the humidity above the sample at equilibrium. These factors can be grouped under two broad categories: osmotic and matrix effects. Due to varying degrees of osmotic and matrix interactions, water activity describes the continuum of energy states of the water in a system. The water appears “bound” by forces to varying degrees. This is a continuum of energy states rather than a static “boundness”. Water activity is sometimes defined as “free”, “bound”, or “available water” in a system. Although these terms are easier to conceptualize, they fail to adequately define all aspects of the concept of water activity. Water activity is very temperature dependent. Temperature changes water activity due to changes in water binding, dissociation of water, solubility of solutes in water, or the state of the matrix. Although solubility of solutes can be a controlling factor, control is usually from the state of the matrix. Since the state of the matrix (e.g. glassy vs. rubbery state) is dependent on temperature, one should not be surprised that temperature affects the water activity of the food. The temperature dependence of water activity varies between substances. Some substances have increased water activity with increasing temperature, while others show a decrease with increasing temperature. Most high moisture foods have negligible change with temperature. One can therefore not predict even the direction of the change of water activity with temperature, since it depends on how temperature affects the factors that control water activity in the substance. Water activity can be used to predict the direction of water movement - water will show net diffusion from regions of high water activity to regions of low water activity. For example, if honey (aw ≈ 0.6) is exposed to humid air (aw ≈ 0.7) the honey will absorb water from the air. Other examples of this dynamic property of water activity are; moisture migration in multidomain foods (e.g. cracker-cheese sandwich), the movement of water from soil to the leaves of plants, and cell turgor pressure. Since microbial cells consist of high concentrations of solute surrounded by semipermeable membranes, the osmotic effect on the free energy of the water is important for determining microbial water relations and therefore their growth rates. Higher aw substances tend to support more microorganisms. Bacteria usually require at least 0.91, and fungi at least 0.7. See fermentation.
  • Die Wasseraktivität (auch aw-Wert oder Activity of Water) ist ein Maß für frei verfügbares Wasser in einem Material. Sie ist definiert als Quotient des Wasserdampfdrucks über einem Material (p) zu dem Wasserdampfdruck über reinem Wasser (p0) bei einer bestimmten Temperatur: <math>a_{\rm w} = \frac p p_0</math> Der aw-Wert ist ein wichtiges Maß bezüglich der Haltbarkeit von Lebensmitteln, und beeinflusst das Vorkommen der Mikroorganismen, die unterschiedliche Ansprüche an frei verfügbares Wasser haben. Bei Mangel an freiem Wasser werden die Wachstumsprozesse von einigen wasserliebenden Mikroorganismen verlangsamt, empfindliche Organismen können gar abgetötet werden, xerophile Organismen hingegen wachsen bei sinkendendem Wassergehalt besser. Bei den meisten Mikroorganismen liegt das Wachstumsoptimum bei einem aw-Wert von 0,98–1. Es gibt jedoch Mikroorganismen, die eine deutlich niedrigere Wasseraktivität von bis zu 0,6 tolerieren. Beispiele sind osmophile (zuckerliebende) Hefen oder extrem halophile Bakterien. Die Anpassung an niedrige Wasseraktivität erfolgt durch Synthese oder Aufnahme von kompatiblen Soluten.
  • Actividad acuosase define como la relación que existe entre la presión de vapor de un alimento dado en relación con la presión de vapor del agua pura a la misma temperatura. Se denomina por regla general como aw del idioma inglés Water activity, aw). La actividad acuosa es un parámetro estrechamente ligado a la humedad del alimento lo que permite determinar su capacidad de conservación, de propagación microbiana, etc. La actividad acuosa de un alimento se puede reducir aumentando la concentración de solutos en la fase acuosa de los alimentos mediante la extracción del agua o mediante la adición de nuevos solutos. La actividad acuosa junto con la temperatura, el pH y el oxígeno son los factores que más influyen en la estabilidad de los productos alimenticios.
  • L'activité de l'eau (symbole aw pour activity of water) représente la pression de vapeur d'eau d´un produit humide sur la pression de vapeur saturante à la même température. Ce paramètre traduit les interactions de l'eau avec la matrice de l'aliment. L'activité de l'eau est l'un des principaux paramètres influençant la conservation d'un aliment ou d'un produit pharmaceutique. Les micro-organismes ont besoin d'eau "libre" (libre pour les réactions biochimiques) pour se développer. L'activité de l'eau ne représente pas la teneur en eau (ou humidité) mais bien la disponibilité de cette eau. Plus l'aw est élevé, plus la quantité d'eau libre est élevée (1 étant le maximum), plus les micro-organismes se développeront. L'aw joue aussi un rôle sur la texture de l'aliment. Le contrôle de l'aw est maintentant un paramètre définit validé par l'USP 1112. Afin de diminuer cette activité, on peut : Sécher le produit Ajouter un soluté qui va fixer l'eau et la rendre non-utilisable par les micro-organismes : c'est le salage des produits de charcuterie, par exemple, ou le sucrage des confitures. Comment mesurer l'activité de l'eau Mesure de l'Activité de l'eau
  • 水分活性（すいぶんかっせい）とは食品中の自由水の割合を表す数値で食品の保存性の指標とされる。
  • De term Aw-waarde werd in 1953 geïntroduceerd door W.F. Scott. De Aw-waarde (ook wel wateractiviteit of Activity of Water genoemd) is een maat voor de hoeveelheid vrij water die aanwezig is in een product. Per definitie is de Aw-waarde van zuiver water gelijk aan 1. Men meet de relatieve vochtigheid van de lucht rond het product wanneer er een evenwicht is ontstaan tussen het product en de lucht die zich rond het product bevindt. Met andere woorden : men meet de vochtigheid van de lucht wanneer deze geen vocht meer gaat onttrekken aan het product of omgekeerd. De Aw-waarde wordt bepaald met een hygrometer.
  • Vannaktivitet (aw) er avhengig av saltinnholddet og vanninnholdet i stoffet. Om vannaktiviteten er under 0,90 regnes det for så lite vann at de fleste mikrober får problemer med å formere seg. Sopp kan likevel formere seg helt ned til 0,75 aw og 0,6 er satt som en grense for kommersielle tørre produkter som skal oppbevares lengre enn ett år. 1,00 er rent vann, og 0,00 er knusktørt. aw = P/P0 = EHR/100 P = partiellt damptrykk til vann i en matvare ved temperatur T P0 = metnings damptrykk til rent vann ved temperatur T EHR = relativ fuktighet ved T (equilibrium relative humidity) - tar hensym til assosiering av vann med andre komponenter - bedre mål på holdbarhet enn mendge vann.
  • A atividade aquosa (denominada também como atividade da água) define-se como a relação que existe entre a pressão de vapor de um alimento dado em relação com a pressão do vapor de água pura à mesma temperatura e varia de 0 a 1. Denomina-se pela regra geral como Aw . A atividade aquosa é um parâmetro inteiramente ligado à umidade do alimento o que permite determinar sua capacidade de conservação, de propagação microbiana, etc. A atividade aquosa de um alimento pode ser reduzida aumentando a concentração de solutos na fase aquosa dos alimentos mediante a extração da água ou mediante a adição de novos solutos. A atividade aquosa junto a temperatura, o pH e o oxigênio, são os fatores que mais influenciam na estabilidade dos produtos alimentícios.
  • 水活性（Water Activity，又稱水分活度、水活度，簡寫aw）指的是在密閉空間中，某一種食品的平衡蒸氣壓與相同溫度下純水的飽和蒸氣壓的比值。純水的水活性等於1.0。水活性所量度的是食物中的自由水分子，而這些水分子是微生物生殖和存活的必需品。大部份生鮮食品的水活性是0.99，而可以抑止多數細菌增長的水活性大約是0.91。
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  • Water activity is a dimensionless quantity used to represent the energy status of the water in a system. It is defined as the vapor pressure of water above a sample divided by that of pure water at the same temperature; therefore, pure distilled water has a water activity of exactly one. It is widely used in food science as a simple, straightforward measure of the dryness of food; foods typically have an optimum water activity at which they have the longest shelf life.
  • Die Wasseraktivität (auch aw-Wert oder Activity of Water) ist ein Maß für frei verfügbares Wasser in einem Material.
  • Actividad acuosase define como la relación que existe entre la presión de vapor de un alimento dado en relación con la presión de vapor del agua pura a la misma temperatura. Se denomina por regla general como aw del idioma inglés Water activity, aw). La actividad acuosa es un parámetro estrechamente ligado a la humedad del alimento lo que permite determinar su capacidad de conservación, de propagación microbiana, etc.
  • L'activité de l'eau (symbole aw pour activity of water) représente la pression de vapeur d'eau d´un produit humide sur la pression de vapeur saturante à la même température. Ce paramètre traduit les interactions de l'eau avec la matrice de l'aliment. L'activité de l'eau est l'un des principaux paramètres influençant la conservation d'un aliment ou d'un produit pharmaceutique. Les micro-organismes ont besoin d'eau "libre" (libre pour les réactions biochimiques) pour se développer.
  • 水分活性（すいぶんかっせい）とは食品中の自由水の割合を表す数値で食品の保存性の指標とされる。
  • De term Aw-waarde werd in 1953 geïntroduceerd door W.F. Scott. De Aw-waarde (ook wel wateractiviteit of Activity of Water genoemd) is een maat voor de hoeveelheid vrij water die aanwezig is in een product. Per definitie is de Aw-waarde van zuiver water gelijk aan 1. Men meet de relatieve vochtigheid van de lucht rond het product wanneer er een evenwicht is ontstaan tussen het product en de lucht die zich rond het product bevindt.
  • Vannaktivitet (aw) er avhengig av saltinnholddet og vanninnholdet i stoffet. Om vannaktiviteten er under 0,90 regnes det for så lite vann at de fleste mikrober får problemer med å formere seg. Sopp kan likevel formere seg helt ned til 0,75 aw og 0,6 er satt som en grense for kommersielle tørre produkter som skal oppbevares lengre enn ett år. 1,00 er rent vann, og 0,00 er knusktørt.
  • A atividade aquosa (denominada também como atividade da água) define-se como a relação que existe entre a pressão de vapor de um alimento dado em relação com a pressão do vapor de água pura à mesma temperatura e varia de 0 a 1. Denomina-se pela regra geral como Aw . A atividade aquosa é um parâmetro inteiramente ligado à umidade do alimento o que permite determinar sua capacidade de conservação, de propagação microbiana, etc.
  • 水活性（Water Activity，又稱水分活度、水活度，簡寫aw）指的是在密閉空間中，某一種食品的平衡蒸氣壓與相同溫度下純水的飽和蒸氣壓的比值。純水的水活性等於1.0。水活性所量度的是食物中的自由水分子，而這些水分子是微生物生殖和存活的必需品。大部份生鮮食品的水活性是0.99，而可以抑止多數細菌增長的水活性大約是0.91。
rdfs:label
  • Water activity
  • Aw-Wert
  • Actividad acuosa
  • Activité de l'eau
  • 水分活性
  • Aw-waarde
  • Vannaktivitet
  • Atividade aquosa
  • 水活性
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