Sorption equilibrium moisture and isosteric heat of Chinese wheat flours

Abstract

Data on equilibrium moisture content (EMC) for six Chinese wheat flour varieties were collected by a gravimetric method at 11-96% equilibrium relative humidity (ERH) and a temperature range of 10-35 °C. Six models were fitted to the sorption data, with the modified Guggenheim Anderson deBoer equation, modified Henderson equation (MHE), and a polynomial equation being the best fits. At a constant ERH, the EMC was negatively correlated with temperature, whereas there was a strong effect of temperature on the sorption isotherms of the wheat flours. Initially, the isosteric heats of adsorption for the wheat flours decreased rapidly with increasing sample moisture content (MC); however, when MC was higher than 15% of the wet basis, further increases in MC caused a slight decrease in heat adsorption values. The heat of vaporisation of the wheat flours approached the latent heat of pure water at a moisture content of ~17.5% wet basis, which was ~2,500 kJ/kg. The isosteric heat of sorption values of the wheat flo...