EFFECT OF TEMPERATURE AND MOISTURE ON THE MECHANICAL PROPERTIES OF OAT

Abstract

In addition to grain drying on the farm, food processing of oats involves heat treatments at the mill withtemperatures up to 100.C and moisture contents from 9.5% to 18%. Addition of heat and water may modify the viscoelasticproperties of the grains and influence product quality. Oat grains were sanded into uniformly thick pieces and tested usingdynamic mechanical analysis (DMA) over a range of temperatures (-20.C to 100.C). Heating oats decreases their stiffness,as indicated by a decrease in storage modulus (E') until 36.C to 57.C. Thereafter, E' increases until 100.C. Moisture alsoaffects E'; at water activities from 0.114 to 0.443, it increases stiffness. However, at higher water activities, it has a plasticizingeffect. The effect of reheating on E' was markedly different, and the value of E' at the start of the measurement was higherthan at the start of first heating, suggesting that heating caused a permanent change in the macromolecular structure. Theseresults suggest that changes in the mechanical properties may occur even at grain drying temperatures.