Estimating equilibrium moisture content from relatively short sorption experiments

摘要

Experimental determination of the equilibrium moisture (M-E) content of food, especially by the static method at high water activities (a(w)'s) or relative humidities (RH's), can be an issue. Here, we proposed a mathematical method for estimating the M-E value at a given a(w) or RH from data obtained at shorter exposure times than those needed to reach constant weight (or equilibrium). The method, based on a flexible empirical sorption model, requires the initial and two subsequent moisture content determinations. Its applicability has been tested with published moisture sorption data on cassava flour film, casein, freeze-dried apple puree and plantain flour. Moisture contents after 24 h predicted with the model from data obtained in 3-12 h agreed with the reported experimental ones within approximate to 2%. This suggests that ME content estimates can be obtained from static data in 24 h or less, depending on the a(w), or RH. The procedure has been automated and posted online as a freely downloadable interactive Wolfram Demonstration. The concept and method can also be implemented in dynamic methods to shorten their cycle, and/or improve their estimates whenever reaching constant weight is uncertain. It is also shown that, in principle, the method can be used for M-E's estimation in desorption.