QUANTIFYING THE RELATIONSHIP BETWEEN RICE STARCH GELATINIZATION AND MOISTURE-ELECTRICAL CONDUCTIVITY OF PADDY DURING SOAKING

This study formulates a mathematical relationship correlating the degree of starch gelatinization (DSG) of rice to the paddy moisture-electrical conductivity (EC) of paddy water during the soaking portion of the parboiling process. DSG values of rice were measured using differential scanning calorimetry (DSC). Paddy was parboiled by soaking at 60, 65, 70 and 75C. At each temperature paddy samples were selected at five different soaking times. Optimum soaking times for 60, 65, 70 and 75C were determined to be 240, 180, 120 and 80 min, respectively. Paddy moisture (22.43-34.93%, wet basis), EC of paddy water (1.63-2.71 mS/cm) and DSG of rice (5.38-36.90%) increased with increasing temperature and soaking time. It was found that a linear relationship exists between DSG and EC, as well as between DSG and moisture content during soaking. EC of paddy water correlates well with DSG of rice during soaking. An online measurement system of paddy water EC was manufactured and evaluated. The relationship between DSG and EC can be utilized for quick and simple determination of DSG during soaking and eliminating the need for conventional chemical analysis. PRACTICAL APPLICATIONS Parboiled rice enjoys high popularity because of its high nutritional content. The soaking stage is the most important stage of the parboiling process. Soaking conditions (temperature and time of soaking) largely determine the characteristics of the parboiled product and can be evaluated by DSG. Therefore, from an industrial point of view, it is important to apply the best processing conditions for parboiling rough rice. Hot soaking requires precise control because starch granules are gelatinized during soaking. Determination of DSG is commonly done by DSC instrument. This method is associated with high costs and cannot provide online data. Online measurement of EC values of paddy water during soaking can be used to easily and accurately predict the final time of the soaking stage. This study was developed as a quick and easy method for online determination of DSG values during soaking. The method presented here can be used for monitoring and controlling the soaking stage by measuring paddy water EC via an online system based on DSG values during soaking.