Single-frequency dielectric relaxation used to characterize the glass transition time of polydextrose

Dielectric relaxation methods are applicable to powdery materials such as carbohydrates. These materials have relaxations that occur in the milli-Hz range while samples are held at fixed temperatures and fixed water activities, aw, (relativity humidity). Under proper conditions these materials undergo physical changes where the initially glassy powder transitions to an amorphous equilibrium state at the glass transition temperature, Tg. Determining this transition involves characterizing the boundary curve (Tg versus aw) which determines Tg and aw conditions where materials are stable with long-shelf life or unstable with very a short shelf-life. This paper serves to illustrate multiple methodologies which can be used to characterize glass transition from frequency-spectra. Three methodologies are described: peak-broadening, peak-shift, and single-frequency. The new single frequency method not only provides results that identical to those of the peak-shift method but increases the data acquisition speeds by a factor of 5. This method is illustrated on polydextrose, a common sugar substitute. The information gathered can then be used to construct the boundary curve which is used to characterize the shelf-life of a material at various conditions.