Investigation of Soaking Temperature in Parboiling Process on Gelatinization Temperature of Fajr Rice Starch in Gorgan: A Method for Modelling the Mass diffusion of Water into Grain

 Rice parboiling process, hydrothermal process of paddy and / or brown rice are among the important processes in the rice industry and include three main stages of soaking in water, evaporation and drying. Due to the increased digestibility of grains following gelatinization, achieving a suitable level of gelatinization n the soaking stage is a basic and essential step in parboiling process.

In this study, Fajr rice varieties were collected from agricultural fields in Gorgan and soaked at temperatures of 35, 45, 55 and 60 °C. Sampling was performed at different time. The gelatinization temperature of rice grains was modelled by calculating the mass permeation constant (Def) of paddy water with Fick model. Then, the approximate temperature of grain gelatinization was determined by Arrinius equation.

The data obtained from adsorption had a good fit in terms of dry moisture content under laboratory conditions with Fick equation and this model properly explained the water absorption behaviour of the samples. Soaking at higher temperatures resulted in faster water absorption. The water adsorption behaviour of the seeds showed that at a temperature of 60 ° C, the seeds do not tend to reach equilibrium moisture and a downward trend was observed in their diagram. Also, with increasing temperature, the Def increased. The Def brown grain was 2.7 times that of paddyو while The Def withe grain was 4.1 times that of brown bean. The R 2 and RMSE obtained for each soaking temperature condition showed that Rice peeling until the brown grain reached and then soaking the brown grain (instead of paddy) could be more effective.

 Using graph and Arrhenius equation, the optimal soaking conditions of Fajr grains for 2 hours at 45 °C were determined.