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Comparatively Speaking: Water Content vs. Water Activity
By: Anthony J. O'Lenick, Jr., Siltech LLC
Posted: December 29, 2010
page 2 of 2
For many years, researchers tried to equate bacterial growth potential with water content but found the values were not universal; rather, they were specific to each food product.
In 1953, W. J. Scott first established that it was water activity, not water content, that correlated with bacterial growth, and it is now firmly established that growth of bacteria is inhibited at specific water activity values. US Food and Drug Administration regulations for intermediate moisture foods are based on these values.
Further, water activity is related to moisture content in a non-linear relationship known as a moisture sorption isotherm curve. These isotherms are substance- and temperature-specific and can be used to help predict product stability over time and under different storage conditions.