Determination of Williams-Landel-Ferry constants for a food polymer system: Effect of water activity and moisture content

The Williams-Landel-Ferry (WLF) equation is a useful tool in the prediction of temperature-induced physical changes in foods that are exposed to speci fic food processing and storage conditions, because so many deteriorative p rocesses are diffusion controlled. In food polymers, viscoelastic propertie s are a strong function of the key plasticizers present in foods, such as w ater. However, WLF constants as a function of water content and water activ ity are not available in the food literature. In this research, we investig ated the WLF properties of soy flour as a function of water activity and el ucidated the effect of water on the magnitude of WLF constants. Based on a time-temperature superposition principle, shift factors (a(T)) were obtaine d, which were used to estimate WLF constants. WLF constants for soy flour w ere shown to be material specific and different from the "universal values. " (C) 2001 The Society of Rheology.