Measurement of Resistant Starch Content in Polished Rice and Processed Rice Products

The resistant starch (RS) content in polished rice and processed rice products (boiled rice and rice crackers) was measured by the Prosky method, the RS-kit method, and the artificial digestion method (ADM). The RS content of rice crackers and cooked rice measured by the Prosky method was 0,65 or less. There are some differences in the conditions of the Prosky method and in the human digestive tract. Therefore, it is difficult to compare the effects of different processing methods and of different varieties of rice on RS content. For measurement by the RS-kit method, RS content of milled rice was about 20%, while the largest value was about 2% in boiled rice or rice crackers, and measurement by RS-kit method corresponded to RS content in a narrow sense. For measurement by the ADM, RS content of the milled rice was about 80016, while the largest value for boiled rice and rice crackers was about 20%. Thus, ADM seems to also be suitable for making comparisons among processed rice products which undergo cooking processes and also reflects the actual digestibility in the human body. Based on the results of comparison testing among various rice cultivars, RS content was shown to decrease after cooking processes, although it did not differ among milled rice samples of different cultivars as measured by the RS-kit method and ADM. The RS of processed rice products prepared from high amylose rice remained higher compared with that from low amylose rice. These findings indicate that RS content can be adjusted through conditions of heating and cooking, because RS differs with different processing methods.