Abstract:To change the functional characteristics of Gastrodia elata Blume starch processing and expand its application scope，this paper mainly analyzed the effect of ultrasonic power on the molecular structure and physicochemical properties of the starch. The research results showed that，with the increase of ultrasonic power，L* and whiteness （W*） were gradually increased，while a* and b* were gradually decreased，indicating that ultrasonic treatment broke the molecular chains of the starch. The surface of starch granules became more regular and smoother，with more uniform scattering and reflection of light. The ultrasonic treatment had a cleaning effect on the impurities in the starch，and could trigger changes in the starch groups，altering the light absorption characteristics，and enhancing the reflection of short-wavelength light such as blue light. Additionally，decreased saturation indicated that ultrasonic treatment damaged the surface structure and molecular structure of starch granules，changing their absorption and reflection abilities of light at different wavelengths. Fourier transform infrared spectroscopy （FT-IR） showed that as ultrasonic power was increased，the intensities of the characteristic peaks for the starch were significantly increased at 1 065 cm-1（C—O stretching vibration） and 970 cm-1 （α-glycosidic bond），indicating an intensified degree of molecular chain breakage. The X-ray diffraction （XRD） results indicated that ultrasonic treatment，with cavitation and mechanical effects，disrupted the molecular chain conformations and weak interactions in the non-crystalline region of the starch，promoted molecular chain rearrangement，and significantly improved the regularity，thus leading to increased starch crystallinity. The thermogravimetric analysis （TGA） revealed that the thermal decomposition temperature and thermal stability of the starch were significantly increased after ultrasonic treatment. The scanning electron microscope （SEM） results suggested that as ultrasonic power was increased，the damage degree of the starch granule surface became higher，effectively improving the freeze-thaw stability and transparency of the starch paste.