Moisture Sorption Characteristics of Selected Commercial Flours (Wheat, Rice and Corn) of Bangladesh

Moisture sorption isotherms of commercial wheat flour, rice flour and corn flour were determined within the water activity range of 0.11-0.93 at different temperatures (5°C, 30°C and 55°C) using the static gravimetric method. The moisture sorption isotherm of all flours exhibited type II characteristics according to BET classification. It was found that corn flour had a higher sorption capacity than wheat and rice flour. Temperature influence on sorption behavior was found that, for wheat and corn flour, the sorption capacity decreased with the increase of temperature, while for the rice flour an opposite behavior was observed at water activity value higher than 0.75. The Clausius–Clapeyron equation was used to calculate the net isosteric heat of sorptions. For all flours, the heat of sorption decreased with the increase of EMC.