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Effects of ingredients (salt, sugar, hydroxypropyl methylcellulose, oil, water, yeast, potassium bromate, and soy flour) on the quality of a yeast-leavened rice bread were studied for the formula optimization. From the amylograph curves, it was suggested that hydroxypropyl methylcellulose (HPMC) provided the rice dough with appropriate viscosity necessary to retard the diffusion of gas. Sugar, yeast, and HPMC have shown to affect the rate of gas production. For the baking test, the results of the screening experiment by a two-level fractional factorial design showed that a significantly positive effect on loaf volume was due to HPMC, and a significantly negative effect to soy flour. Very little difference in loaf volume was observed between breads with and without potassium bromate, indicating that the oxidant did not function strongly on the improvement of bread volume. Increasing the levels of HPMC somewhat counteracted the loaf volume-depressing effect of soy flour. Soy flour could be successfully substituted for rice flour at levels up to 4%. Finally, the response surface methodology (RSM) study suggested that 4% soy flour containing rice bread with good volume and grain could be obtained.
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