Modelling and Analysis of Moisture Sorption Isotherm of Raw and Pregelatinized Rice Flour and Its Crystalline Status Pre
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Modelling and Analysis of Moisture Sorption Isotherm of Raw and Pregelatinized Rice Flour and Its Crystalline Status Prediction Soumya Ranjan Purohit 1 & Pavuluri Srinivasa Rao 1
Received: 6 July 2016 / Accepted: 6 December 2016 / Published online: 17 December 2016 # Springer Science+Business Media New York 2016
Abstract 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 (SBET m2/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. Keywords Gelatinization properties . Moisture adsorption isotherm . Rice flour . Surface area . Crystalline status * Soumya Ranjan Purohit [email protected] Pavuluri Srinivasa Rao [email protected] 1
Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India
Introduction Moisture adsorption isotherm illustrates the relationship between moisture content and the water activity (aw) of a material at a definite temperature and pressure. It is also an useful tool to explore the interaction of water in relation to food and its composition (Viollaz and Rovedo 1999). Such an important interaction occurs during gelatinization process, in which starch and water interact with each other. Starch consists of two polymers that contribute to its molecular structure, i.e. amylose, the linear molecule and amylopectin, a highly branched molecule. Both molecules form an alternate crystalline and amorphous structure, where amylopectin forms most of the crystalline part along with some part of amylose. However, the amorphous region is characterized by the presence loosely packed amylose (Resio et al. 2005). As natural phenomena, these amorphous zones are more accessible to water than the crystalline regions. As a result, amylose molecule leached out from the starch matrix during hydrothermal treatments (Beli
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