GC STUDY OF THE EFFECT OF SPECIFIC-HEAT TREATMENT ON WATER SORPTION BY WHEAT AND SOY FLOUR

The water sorption isotherms of wheat and soy flour were constructed a t 30-degrees-C using the computerized inverse gas chromatographic tech nique. Wheat flour showed a higher sorptive capacity than soy flour. T his was attributed to the higher sorptive capacity of starch, the main constituent of wheat flour as compared to that of protein, the main c onstituent of soy flour. Subsequently the flour samples were heat-trea ted at 150-degrees-C for 3, 6, 12, and 24 h in the dry state. Sorption data showed a reduced water uptake both for wheat and soy flour for a ll heating periods ranging between 7.1 and 21.7% for wheat flour and b etween 7.9 and 31.6% for soy flour. The higher reduction in water upta ke of the soy flour was correlated with the stronger effect of heat, t reatment on proteins than that on carbohydrates. Sorption data were fi tted to the (Brunauer, Emmett, Teller) isotherm model and the heat of hydration of the flours was calculated.