Degree of Gelatinization of Starch during the Cooking Process of Rice

Abstract

Rice is usually eaten as easily digestible form by heating with water. On rice cooking, the amount of water added to rice and heating conditions are extremely important factors to obtain palatable cooked rice. These conditions are more critical compared with other starchy foods. The purpose of this study is to find the best cooking conditions of rice in terms of the gelatinization of starch during the heating process and the palatability of the rice. The degree of gelatinization of starch was determined by BAP method, turbity method, X-ray diffraction and differential scanning calorimetry (DSC). Three different heating conditions were examined, quick heating process which took 8 min to boiling, slow heating process which took 25min to boiling, and two steps of cooking process where rice was held for 20min at 60°C, then heated to boiling in 5min. These experiments lead to the following results. The degrees of gelatinization of starches were almost same by either quick heating or slow heating. The results of sensory analysis showed that the former was hard and the latter was soft in texture. On the other hand, cooked rice obtained by two steps of cooking process showed that starch was sufficiently gelatinized, and the palatability of cooked rice was the best among the samples examined. During the first step where rice grains were held for 20min at 60°C, water could be absorbed into rice grain. Then during the second step where quick heating applied for 5min to boiling, rice starch could completely be gelatinized.