Moisture sorption profiles of food products have provided useful information to researchers for decades and through automation have become much easier to produce. Automation has also facilitated the production of dynamic moisture curves that eliminate the time consuming equilibration step of traditional sorption methods by directly measuring changes in water activity. The most common method for generating dynamic moisture curves is the Dynamic Dewpoint Isotherm (DDI) method. For DDI, adsorption occurs as saturated wet air is passed over the sample, while desorption is accomplished as desiccated air is passed over the sample. After roughly a 0.01 change in water activity, airflow is stopped and a snapshot of the sorption process is taken by directly measuring the water activity and the weight. The method is dynamic and non-equilibrium because the water activity is constantly changing during the test. The advantages of the DDI method are increased analysis speed (since the sample does not have to wait for equilibration to a known water activity) and an unmatched level of resolution. Research, initiated by scientists working at Decagon Devices, Inc., discovered that the increased data resolution of DDI allows for the visualization of abrupt changes in sorption properties not previously seen with traditional moisture sorption methods. It has been determined that sharp inflections in DDI curves due to drastic changes in moisture sorption properties correspond with changes in the matrix leading to undesirable changes in product stability. The water activity that corresponds with a sharp inflection in the DDI curve has been identified as the critical water activity. In the decade since the development of the patented DDI method, researchers have been able to link the critical water activity from DDI to glass transition, changes in texture, changes in permeability, susceptibility to clumping, and amorphous content. Typically, generating a DDI curve to identify the critical water activity is much easier than the alternative investigation that would be required to track stability changes due to changes in water activity. Researchers around the world now routinely rely on DDI curves to facilitate the identification of optimal water activity specifications and minimize unexpected loss of stability due to moisture interactions in foods.

A decade of work: Developing applications for dynamic moisture sorption curves

255th National Meeting (2018)

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