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  • Resumen es exacto "Rice is a staple food for more than two thirds of the world’s population. It is composed of carbohydrates, proteins, vitamins and virtually no fat. Whole grain rice yields and process time could be optimized through the study of the drying process. This may result in a larger fraction of the crop entering the human food chain, enhancing the value of the crop, and resulting in a smaller fraction of broken grain, which command a lower market value.
    In this study, several mathematical models have been fitted to experimental data and then compared by means of a meticulous statistical analysis. In this way, equations that can be used to predict the desired information with accuracy were chosen, and relevant parameters were obtained, which can be used by industry workers for future predictions. No data of the drying behaviour of rice IRGA 424, a variety widely used in Argentina, was available before this work.
    Glass transition temperature (Tg) of IRGA 424 was satisfactorily determined by dynamic mechanical analysis tests. Tg was calculated using the peaks of the curves
    of the loss modulus (Tgmidpoint) and the tangent delta (TgEndset) as a function of temperature. A state diagram was obtained, specific for that cultivar. The values found for the rice variety IRGA 424 increased from 42.13 to 104.69 ° C, as the moisture content of the samples decreased from 22.3% to 9.3%. Using statistical estimators, five mathematical models were evaluated to determine their ability to predict the glass transition temperature as a function of the water content of the rice samples: Gordon y Taylor simple and linearilized (Gordon y Taylor 1952); Fox
    (Fox, 1956); Jenkel y Heusch (Jenkel y Heusch, 1953) and Kwei (Kwei, 1984). The best fit was obtained with the linearized Gordon-Taylor equation.
    A new mathematical model was developed to predict the glass transition temperature of IRGA 424, whose statistical evaluation produced satisfactory results.
    In order to preserve the quality of the rice, the gradients of moisture content within the grain and differences in the state of the material to achieve higher rice yields must be minimized. The optimal operating values to achieve this objective are drying temperature equal to 40.0 ° C, temperature time of 40 minutes and initial moisture content at the beginning of the tempering of 18.8%. Under these conditions, the total processing time needed to reach 13% moisture content is 105 minutes.
    Drying and tempering rice IRGA 424 at a temperature of 40 ° C is the best alternative of all studied, since the rice remains in the glassy region throughout the process. The thin-layer drying parameters were calculated from the mathematical fitting of seven drying equations of the literature: Lewis (Lewis, 1921); Page (Page, 1949); Henderson y Pabis (Henderson and Pabis, 1961); Logarithmic (Yaldiz and Ertekin, 2001); Two terms (Henderson, 1974), Midili (Midili et. al. 2002) y Logístico (Chandra and Singh, 1995). The best goodness of fit was obtained with the Page model, whose parameter n, was not affected by drying temperature."
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