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    Study of pH Changes of Rice and Suitable Condition of Mixed Indicator Solution for Developing a Simple Rice Age Test Kit
    (The Journal of KMUTNB, 2023) Kittisak Wasantiwong; Rungtiwa Wongsagonsup; Dusit Angthararuk; Jeerun Kingkaew
    Rice grains encounter the changes of physicochemical properties along the storage periods, thus affecting the cooking and eating properties. This research aims to study the pH changes of stored rice cultivars during different storage times and to find the suitable condition of mixed indicator solution between Methyl red and Bromothymol blue for developing a simple test kit for age estimation of stored rice. The rice cultivars used were RD 6, Khao Dawk Mali 105, and Phitsanulok 2, which were stored for 0–12 months at room temperature. The results showed that for rice with increasing storage time, pH value of rice decreased. The pH of RD 6, Khao Dawk Mali 105, and Phitsanulok 2 rice cultivars decreased from 6.82–6.45, from 7.09 to 6.45 and from 7.03–6.49, respectively. The color of the mixed indicator solution changed according to the pH value of phosphate buffer (pH 5.8–7.2). The suitable condition giving the most obvious color differences in pH 5.8-7.2 of mixed indicator solution between Methyl red and Bromothymol blue was at ratio of 60 : 40 and volume of 0.30 ml. When the stored rice samples of varying ages were tested with the optimum mixed indicator solution, the solution color changed from green to yellow and orange with the increasing storage times of rice. This can be used for developing a simple test kit for age estimation of stored rice and would also solve the problem of adulteration of fresh and aged rice.