Determination of the bulk moisture diffusion coefficient for corn starch using an automated water sorption instrument

The bulk moisture diffusion coefficient (D_b) is an important physical parameter of food ingredients and systems. However, the traditional method of measuring D_b using saturated salt solutions is very time-consuming and cumbersome. New automated water sorption instruments, which can be used to conveniently and precisely control both relative humidity and temperature, provide a faster, more robust method for collecting the data needed for determining D_b. Thus, the objectives of this study were to (1) investigate the use of the DVS instrument for collecting the data needed for determining the adsorption (D_ba) and desorption (D_bd) bulk moisture diffusion coefficients for dent corn starch as a function of relative humidity and (2) determine the effect of temperature on D_ba for dent corn starch at a constant relative humidity. Kinetic water sorption profiles of dent corn starch were obtained at eight relative humidity values ranging from 10 to 80% at 10% intervals at 25°C and at five temperatures, 15, 20, 25, 30, and 35°C, at 50% relative humidity using a DVS instrument. D_b was calculated from the kinetic water sorption profiles using the full solution of Fick's second law for the thin slab model, as well as the slope method, a simplification of the full model. The D_ba of dent corn starch at 25°C reached a maximum at intermediate relative humidity values, after which D_ba decreased due to a change in the moisture diffusion mechanism from vapor to liquid diffusion. The D_bd of dent corn starch at 25°C remained nearly constant as a function of relative humidity. The D _ba for dent corn starch increased as temperature increased from 15 to 35°C, with an activation energy of 38.85 ± 0.433 kJ/mol.