Determination of the Bulk Moisture Diffusion Coefficient for Corn Starch Using an Automated Water Sorption Instrument

摘要

The bulk moisture diffusion coefficient(Db)is an important physical parameter of food ingredients and systems.However,the traditional method of measuring Db 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.