Relative humidity equilibrium

Norrish, R.S. 1966. An equation for the activity coefficients and equilibrium relative humidities of water in confectionery syrups. J. Food Technol. 1, 25-39. 

The effects of fungal fermentation on the moisture adsorption and retention properties of defatted peanut flour have been reported (28). At 8 and 21OC, little difference was noted between the moisture contents of freeze-dried ferments and untreated samples equilibrated at relative humidities ranging from 14 to 75%. However, marked changes were noted above 75% equilibrium relative humidity (ERH), where the control samples did not adsorb as much moisture as did the ferments. These differences were attributed to an increased ratio of exposed hydrophilic to hydrophobic groups resulting from fermentation. 

For a food system in equilibrium with a gaseous atmosphere (i.e. no net gain or loss of moisture to or from the system caused by differences in the vapour pressure of water), the equilibrium relative humidity (ERH) is related to aw by ... 

Snavely, M.J., Price, J.C., and Jun, H.W. 1990. A comparison of three equilibrium relative humidity measuring devices. Drug Dev. Industrial Pharm. 16 1399-1409. 

Water activity, a thermodynamic property, is defined as the ratio of the vapor pressure of water in a system to the vapor pressure of pure water at equal temperature, or the equilibrium relative humidity of the air surrounding the system at equal temperature. 

Smith, PR. 1971. The determination of equilibrium relative humidity or water activity in foods A literature review. The British Food Manufacturing Industries Research Association, U.K. Stekelenburg, F.K. and Labots, H. 1991. Measurement of water activity with an electric hygrometer. Ini. J. Food Sci. Technol. 26 111-116. Stoloff, L. 1978. Calibration of water activity measuring instruments and devices Collaborative study. J. AOAC 61 1166-1178. 

ERH. see Equilibrium relative humidity ESI. see Electrospray ionization Essence oils, see specific listings Esterases, comparison to lipases, 371 Esters... 

ERH equilibrium relative humidity ESI electro spray ionization FAB/MS fast atom bombardment mass spectrometry... 

Equilibrium relative humidity studies have shown that cardamom dried and maintained at or below 10% moisture retains its original colour and avoids mould growth (Govindarajan et al., 1982). If black polyethylene is used, the effect of light is further minimized and safe storage is possible for... 

The extent to which a solute reduces aw is a function of the chemical nature of the solute. The equilibrium relative humidity (ERH) in percentage is ERH/100. ERH is defined as ... 

There are some foods where the equilibrium relative humidity is above that of the external climatic conditions. The packaging material then serves the purpose of protecting the product from moisture loss. This is the case with processed cheese and baked goods. 

Intermediate moisture foods are in the aw range of 0.90 to 0.60. They can achieve stability by a combination of aw with other factors, such as pH, heat, preservatives, and Eh (equilibrium relative humidity). 

Microorganisms and enzymes need water in order to be active preservation of foods can be sought by reducing their moisture content to a point where the food-spoilage of pathogenic microorganisms are inhibited. Scott [ 1,2] called the equilibrium relative humidity (ERH), which is the availability of water in a food medium. Water Activity (a, ). a, is defined as the ratio of vapour pressure (p) of solution to the vapour pressure (Po) of the solvent, usually water ... 

In the solid-state fermentation process, the water activity is variable because of evaporation and metabolism. In order to keep the water activity constant, the humidity of the supplied air should be controlled or a humidifier should be installed in the fermentor. The relationship between the water activity within the solid substrate and the equilibrium relative humidity (ERH) of the surrounding air can be expressed as ... 

Lourdin, D., Coignard, L., Bizot, H., and Colonna, P. Influence of equilibrium relative humidity and plasticizer concentration on the water content and glass transition of starch materials. Polymer, 38, 5401,1997. 

Gerhards (1998) characterized instant coffee agglomerates at different equilibrium relative humidities. Dry agglomerates (aw = 0.11) had a highly jagged relationship typical of brittle materials, while moist agglomerates (aw = 0.69) had a smooth, concave upward curve characteristic of a... 

Aspergillus sp. are common allergens (hay fever, asthma, pneumonitis, etc.). Water requirement on a substrate depends on species, and typically varies between 71 and 94%. This is often described as Aw index, that is, available water index. Aw refers to a range of minimum water requirements, and is expressed as Aw = ERH/100 (air), where ERH is equilibrium relative humidity. Eor Aspergillus species Aw =... 

Relative humidity has been defined by Aguilera and Stanley (1990) using the equation RH (%) = F/po X 100%, where P is the partial water vapor pressure in an atmosphere and po equals the water vapor pressure of pure water at the same temperature. Thus, the water activity of a food can be determined by the prevalent relative humidity in the atmosphere surrounding the food when in an equilibrium state. It can be expressed by the equation a = F/po = RH% X 1/100 (in equilibrium state) = ERH% X 1/100, where ERH is an expression of equilibrium relative humidity (Watson and Harper, 1987). 

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