Effect of Storage Temperature on Biochemical and Mixolab Pasting Properties of Chinese Japonica Paddy

This study investigated the changes in germination rate, contents of oleic acids, protein, water soluble sugars, enthalpy of flour gelatinization, and Mixolab dough pasting properties of three varieties of japonica rough rice after 18-month storage at four temperatures of 4,15,25 and 35 ºC. After an 18-month storage, the paddy stored at or below 25 ºC had more than 70% germination rate, their flour extracts by acid dye mixture of methyl red and bromothymol blue showed greenish color, but the paddy stored at 35 ºC was only 30% germination rates, their flour extracts by acid dye mixture seem to be yellowish. With an increase in storage temperature, mositure content in paddy decreased, but total protein changed unsignificantly. In comparison to the paddy stored at 15 ºC, the higher storage temperature (25 and 35 ºC) tends to decrease the contents of damaged starch, water-soluble reducing sugars, total sugars, and uronic acids. The content of oleic acid in paddy stored at 4 ºC was markedly higher than that at the temperatures of 15, 25 and 35 ºC. Compared to lower temperate (4 and 15 ºC), the higher storage temperature (35 ºC) increased the gelatinization enthalpy of paddy flour and its starch determined by a differential scanning calorimetry (DSC), also increased Mixolab characteristic torque parameters such as starch gelatinization peak (C3), starch gelatinization minimum (C4), starch retrogradation minimum (C5), degrees of starch decay (C3-C4) and retrogradation (C5-C4) with a decrease in protein weakening (C2). The results of this study indicate storage temperature is an important factor affecting the physiological and biochemical properties of paddy, and lower temperature below room temperature are recommended to maintain paddy quality.