Effect of Drying Methods on Drying Characteristics and Quality of Instant Coix Seed Flour

The instant coix seed flour was prepared by microwave drying (MD), microwave convection drying (MCD), hot air drying (HAD) and traditional roasting (TR) and their drying and rehydration characteristics, color, nutritional compound, solubility property and sensory evaluation were compared. The results showed that in terms of drying characteristics, MCD took the shortest time, only 26 min, followed by TR, 35 min, and HAD had the longest time, 90 min. And MCD had the highest average drying rate. In terms of color, the sample treated by MCD method was yellowish, which was closer to the color of fresh coix powder. In terms of nutritional compound, drying caused the lost of the contents of ash, crude fat, protein, total sugar and reducing sugar in dried coix seed flour. MD had the least loss of ash and total sugar, MCD had the best retention of protein and reducing sugar, and TR had the highest content of crude fat of 7.02 g/100 g. In terms of solubility property, MCD prepared products had the lowest bulk density, the lowest angle of repose, the best fluidity and the highest hydration ability, while TR prepared coix powder had the shortest wettability and dispersibility time, and the lowest caking rate and moisture absorption rate. MCD samples obtained the highest sensory values of 84.8. Through comprehensive evaluation, MCD with the highest drying efficiency and the best quality.