Effect of Different Drying Methods on Quality and Antioxidant of Instant Millet Flour

The nutritional content, physical and antioxidant properties of four types high quality pure natural instant millet flour prepared by microwave vacuum drying (MVD) and microwave hot air drying (MHAD), hot air drying (HAD) and traditional roasting (TR) were studied. The results showed that the contents of nutrients, and antioxidant activity in vitro decreased and the characteristics of the millet flour enhanced after drying treatment compared to fresh sample. The highest contents of crude fat, protein and polyphenol were obtained by MHAD, 2.64, 8.63 and 57.2 g/100 g, respectively. Meanwhile, the free radical scavenging ability of DPPH·, superoxide anion and reducing power were the highest with the IC₅₀ values of 0.138 and 0.134mg/mL, respectively. The reducing power was 1.98. The powder of MHAD had the best fluidity, the lowest hygroscopicity (39.34%), the lowest caking degree (17.01%), the highest iodine blue value (0.685), and the highest sensory evaluation scores (95.2 points). The contents of yellow pigment in millet flour prepared by MVD method was the highest (67.22 mg/100 g), and the ability of scavenging hydroxyl radical was the strongest (IC₅₀ was 0.059 mg/mL). Comprehensive analysis, microwave hot air drying method could keep the nutritional components of instant millet flour completely with good quality and strong antioxidant activity. It could be used as a new economical and energy-saving drying method for the preparation of millet flour.