Changes in Intergranular Air Properties of Grain Bulk and Quality Parameters in Japonica Paddy with Slightly High Moisture during Storage

In order to evaluate the quality parameters for short-term stored paddy with slightly high moisture, this study determined the changes in intergranular air relative humidity (RH) and wetbulb temperature of grain bulk with an equilibrium moisture model and Newton-Raphson method, and analyzed the effect of their accumulation amount during storage on thermal and thermo-mechanical properties, and lipid components, and appearance quality indexes in milled rice. The japonica paddy with 15.3% MC was put into warehouse in winter and stored for 163 days, when the average dry temperature in bulk increased from 8.3 to 22.9°C, the average RH in bulk layer 1, 2, 3, and 4 respectively increased 3.6%, 3.0%, 2.9%, and 2.9% from 75.1%, and wetbulb temperature respectively increased 15.21, 13.57, 13.47 and 13.29 °C from 6.2 °C, showing no damage from stored insects and fungi. The gelatinization peak temperature of rice flour measured by DSC remained unchanged. A Mixolab analysis showed, during paddy storage from 45 to 213 d, dough development time and stability time, and starch setback torque gradually increased, but enzymatic speed decreased. GC-MS analysis showed the percent of the main fatty acid species kept unchanged during 213 d paddy storage. External indexes like accumulation of grain bulk maximum temperature, and accumulation of wetbulb temperature corresponding to bulk maximum temperature, and internal indexes such as the temperature, area and height of rice flour gelatinization peak measured by DSC, and dough development time and stability time, gelatinization peak torque and enzymatic speed in rice flour measured by a Mixolab, and fatty acid components (C_14:1, C_14:0, C_20:5n3, C_20:3n6, C_20:2, C_20:1, C_24:1, C_24:0), as well as rice appearance quality indexes like head rice percentage, small broken kernel rate, and kernel size could be used as the evaluation indexes for the low temperature storage of a japonica paddy with slightly high moisture.