Ultrasound Assisted Extraction of Yam (Dioscorea bulbifera) Starch: Effect on Morphology and Functional Properties

After the grinding stage of yam tubers, ultrasonic treatment (UT) is compared to traditional starch extraction. Different sonication conditions of amplitude (12, 40, and 68%) and time (3, 6, and 9min) are evaluated along two other treatments: a control (0% amplitude) and 70% amplitude for 15min, in order to compare the traditional extraction method and extreme ultrasonic conditions. Extraction yield, centesimal composition, color instrumental analysis, scanning electron microscopy, optical microscopy, particle size, x-ray diffraction, swelling power and solubility, paste clarity, pasting properties, thermal properties, and absolute density are used to evaluate the isolated starches. Yield increased from 29.85% (control) to 32.09% (70% amplitude, 15min). The surface of certain sonicated treated starch becomes damaged, also amorphous region is reduced, but no change in the crystalline pattern of starch is observed, characterized as B type. Except for treated starches at 70% amplitude for 15min, all others showed no change or slight increase of peak viscosity. Despite the increase in yield, ultrasound caused changes on physical and chemical characteristics, depending on time and amplitude, hence it may be used as alternative technique for physical starch modification, for example, for producing thickeners agent.