Influence of Heating Temperature on Cooking Curve of Rice
The swelling behavior of a rice grain in water and an aqueous NaCl and acetic acid solution was investigated as a function of temperature. We observed that the rice grain in water shows an abrupt change in shape and size at 61 °C. The transition temperature Tv became higher in an order: sodium chloride aqueous solution > water > acetic acid aqueous solution. In order to clarify Tv, we also investigated kinetics on cooking of rice grains by the rheological measurement. The time development of compliance of rice grains in compression (cooking curve) from 5 to 1440 min was measured in the range of cooking temperatures from 61 to 80°C. We found that Tv is the onset temperature to complete the cooking of rice. The cooking curve at the cooking temperature neighborhood Tv was approximated by the first order reaction with the two different rate constants. The faster and slower reactions were explained as indicating the plasticizing effect of water on rice grains, and mainly the gelatinization of the starch in rice grains, respectively.
KeywordsRice Cooking curve Rheology Kinetics Cooking temperature Phase transition
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