Abstract:Three heat treatments, namely roasting, microwaving, and wet heating, were examined to determine their effects on the color differences, moisture distribution, microstructure, starch crystalline structure, pasting characteristics, and rheological properties of adzuki bean flour using a colorimeter, low-field nuclear magnetic resonance spectrometer, scanning electron microscope, X-ray diffractometer, rapid Visco analyzer, and rheometer. Furthermore, the relationships of different heat treatments on the digestive properties of steamed bread after starch modification were examined. The results showed that the chromaticity changes ΔE were in the following order: microwaving>roasting>wet heating. Heat treatments did not change the C-type structure of adzuki bean flour, but the particle morphology of adzuki bean flour was significantly damaged after roasting and microwaving. The water absorption index and swelling power increased by approximately 25% after heat treatments, but microwaving decreased the S index. Wet heating lowered the peak viscosity, trough viscosity, final viscosity, and setback of adzuki bean flour to 1 031.67, 921.00, 1 541.33, and 620.33 mPa•s, respectively. The reduction was more remarkable than that caused by microwaving and roasting (P<0.05). Wet heating resulted in more significant loss of bound water than the other two methods. Rheological studies suggested increased dough G' and G" as well as viscoelasticity, insignificant changes in tanδ, and improved water-holding capacity. The resistant starch contents of steamed bread increased to 12.8% and 13.69% after roasting and microwaving for 6 min, respectively. This study provides a reference for choosing suitable treatment methods to improve the quality of steamed bread made from adzuki bean flour.
