Effect of Addition of Acid on the palatability and the Staling of Cooked Rice

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The effect of cooking with acetic acid aqueous solution on the chemical and physical properties of rice was examined. Japonica rice, Nipponnbare, was cooked with 0, 0.05, 0.1 and 0.2M aqueous solutions of acetic acid. The rice cooked with acetic acid showed lower hardness and higher stickiness than the rice cooked with water when measured by texturometry. These effects were confirmed by a sensory evaluation. The increased amount of glucose during cooking was higher for the rice cooked with acetic acid than for the rice cooked with water. Reducing sugars and total free amino acids rice were also higher for the rice cooked with acetic acid than for the rice cooked without acid. These tests were conducted on other varieties of rise. Long grain rice from Thailand, Nipponnbare from Shiga-Prefecture, Koshihikari from Niigata-Prefecture and Hiyokumochi from Saga-Prefecture were chosen as samples. The effect of cooking with acetic acid was obviously different according to the variety of rice. … More The breaking strength of the Thai-rice cooked with acetic acid aqueous solution decreased drastically, while the sticking strength increased, the sticking strain hardly changed. On the other hand, the breaking strength and the sticking strength for Hiyokumochi did not change with the addition of acetic acid, while the sticking strain showed obvious increase. The results of cooking with acetic acid on the texture of Nipponnbare and Koshihikari were somewhere between the results for Thai-rice and Hiyokumochi. Finally, the amount of protein that had dissolved into the water when the rice was soaked prior to cooking was measured, since the protein in rice granules is said to prevent the swelling of the starch within. More protein had dissolved into the water containing acetic acid than to the water containing no acid. Especially, prolamine-rich-fraction and glutelin-rich-fraction that dissolved into the water containing acetic acid were higher than the amount that dissolved into the water containing no acid. It is suggested from these results that one of the reasons for the improved texture of rice cooked with acetic acid derives from the solubilization of the protein by this. Less