Comparison of respiration rates from static and dynamic measurement systems for soybeans at 18% moisture and 35°C

The quality of grain is affected by external factors such as temperature (T) and moisture content (w), elevated levels of which can decrease allowable storage time because of accelerated grain deterioration. The maximum allowable storage time(MAST) is the time at which a 0.5% dry matter loss (DML) occurs. MAST can be determined by measuring the respiration rate of grain, i.e. the amount of carbon dioxide (CO2) respired. There are two systems that can be used to measure respired CO2: static and dynamic. Static CO2 measurements are obtained by placing grain in a sealed chamber and monitoring the amount of CO2 respired over time. In a dynamic system, air passes through a bed of grain and carries the respired CO2 into a measurement system. CO2 is not allowed to accumulate within the grain bed. In this study, we developed one static system and another dynamic system to measure and compare the respired CO2, respiration and DML rates of 18% moisture soybeans stored at 35°C. In the static system, CO2 levels inside a sealed chamber were monitored using a sensor package with a built-in data logger for continuous measurement. In the dynamic system, respired CO2 was captured using a CO2 absorbent material, and its weight was monitored at discrete time intervals over the storage period. Multiple tests were conducted, one to establish the DML comparison between the systems and another to identify the stratification of CO2 on the static chamber. For each test, soybeans from the same batch were rewetted to 18% w.b. and held at 35°C for up to 10 d in the static system, and 10 d or until estimated DML exceeded 1.5% in the dynamic system. The measured CO2 concentrations over time were used to calculate the specific mass of respired CO2 (g CO2/kg d.b. beans) and subsequent DML (%). Respiration and DML rates of dynamic system were 12.8 higher than the static, owing to oxygen depletion in the sealed chamber.