Modelling and Analysis of Moisture Sorption Isotherm of Raw and Pregelatinized Rice Flour and Its Crystalline Status Prediction

Moisture sorption behaviour of pregelatinized rice flour, in comparison to raw rice flour was studied. Empirical modelling, analysis of moisture adsorption behaviour and biophysical properties were considered to understand the mechanism of the high moisture sorption behaviour followed by the prediction of crystalline status of flour samples. Type II sorption characteristic was found for both raw and pregelatinized rice flour samples. Monolayer moisture content of 0.0581 and 0.0419 g/g (db), respectively, was obtained for raw and pregelatinized rice flour. BET surface area (S (BET) m(2)/g) of pregelatinized rice flour was found to be less than raw rice flour. Further, a single parameter empirical model was derived to explain the moisture sorption behaviour of rice flour. In the derived model, the model parameter (K) was considered as the crystalline status. Evidently, X-ray diffraction study was used as the confirmatory tool to justify the explanation given for the model term (K). Lower K value obtained for pregelatinized rice flour was indicative of lower crystalline order and higher affinity to absorb moisture. The result obtained out of this work provides a new insight into the high water sorption behaviour of pregelatinized starch. In addition, the empirical model can also be useful for prediction of crystalline status of starchy materials.