Abstract: The hardness, pasting properties and microstructure of adzuki beans during different cooking times were studied by using a texture analyzer, a rapid viscosity analyzer, a scanning electron microscope, X ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The correlation among basic components, hardness, crystallinity, gelatinization degree and pasting properties was also analyzed. The results showed that the contents of starch and protein, pasting properties, hardness and crystallinity showed a descending trend followed by leveling off with the increase of cooking time, while the gelatinization degree showed the opposite trend. However, there was no significant change in fat content (P < 0.05). During cooking, the cross-sectional microstructure of cotyledon cells in adzuki beans changed significantly. The starch granules were completely exposed and showed smooth and regular spherical particles as a result of wider cell gap and the disappearance of cell contour. The infrared spectra showed that cooking could decrease characteristic peak intensity in the sensitive regions, and some fingerprint regions also decreased or even disappeared. Both XRD and FTIR confirmed that structural changes of adzuki bean starch during cooking. Correlation analysis showed that starch, gelatinization degree, pasting properties, hardness and crystallinity had a very significant correlation with each other (P < 0.01).

Key words: adzuki bean, cooking, pasting properties, crystallinity, infrared spectroscopy, microstructure