Estimation of effective diffusivities and glass transition temperature of polydextrose as a function of moisture content

Abstract

The glass transition temperature ( T g) of polydextrose was determined by differential scanning calorimetry as a function of moisture content, and was fitted to the Gordon–Taylor equation. T g decreased with an increase in moisture content, confirming the plasticizing effect of water on polydextrose. The effective diffusivity of water in polydextrose ( D), which increased with an increase in storage water activity ( a w), was estimated at room temperature both above and below the glass transition by applying the method of slopes [Effective water diffusivity in starch materials, MS Thesis, Rutgers University (1987); Effect of gelatinization and sugars on the effective moisture diffusivity in starch materials, MS Thesis, Rutgers University (1988)] to the experimental data. D showed a sharp increase in regions close to the glass transition, where polydextrose changed from the glassy to the rubbery state due to increased mobility. D was also correlated to a model [The effect of water activity on moisture diffusivity in soy flour as determined from a free volume based approach (2002)] based on the free volume theory [J. Appl. Polym. Sci. 22 (1978) 2325; AIChE J. 38 (1992) 405], which captured the change in diffusion mechanism as a function of glass transition.