Drying Characteristics and Lysine Content of Wheat Distiller's Grain with Solubles under Three Drying Methods

Abstract

The drying characteristics and lysine content of wheat distiller's grain with solubles were studied under three methods: forced air drying, microwave drying, and microwave–convective drying. For forced air drying, temperature was set at five levels (40, 60, 80, 100, and 120°C), maintaining air velocity and relative humidity at 0.7–0.8 m/s and less than 8%, respectively. Four power levels (40, 60, 80, and 100%) and four combination settings (130°C–30% power, 150°C–30% power, 160°C–30% power, and 190°C–30% power) of a domestic microwave oven were used for microwave- and microwave convection drying. Experimental data were fitted to four common thin-layer drying models, and the Page model was found to best describe the drying behavior of the distiller's grain under the three methods. Lysine content and the color parameters (L, a, and b) were also determined and assessed for linear correlation with temperature and microwave power. Lysine content and L values decreased with increases in drying air temperature. Lighter colored distiller's dried grains with solubles (DDGS) samples tended to have higher lysine content. Microwave-dried samples did not show significant differences in lysine content and in L values across the four power levels.