In this work, a high shear mixer (HSM) is designed to produce a higher theoretical shear rate than conventional HSM in order to induce structure degradation of cassava starch granules. Using scanning electron microscopy and transmission electron microscopy, the processed cassava starch granule surface changes are identified without any major change in the granule shape. The carbohydrate component analysis and intrinsic viscosity suggest that the structural change is led by the removal of a relatively low-molecular-weight carbohydrate component from the granule. The changes in the crystalline and thermal properties are observed by the degradation process using a HSM. The process using a rotor speed of 15 000 rpm is found to significantly induce granule surface changes and carbohydrate removal. The decrease in granule crystallinity is correlated with an increase in the granule swelling power and solubility.
Cassava starch is one of the biopolymers which can be degraded to many useful products such as reducing sugar, non-reducing sugar and modified starch. However, it has a solid granule structure that can inhibit its degradation process. High shear mixing (HSM) is a well-known method for dissolving biopolymers. Shear effect of HSM created by a narrow slit between rotor and stator which can be increased by the increase of rotational speed. By increasing its shear effect, HSM is able to cut the glycosidic bond of starch to produce reducing sugar. Therefore, this study aims to study the effect of high shear rate to granule structure and reducing sugar product. The HSM process was carried out on the suspension of cassava starch with a concentration of 1/20 (g/mL) for 15 min at various stirring speeds (5000-15000 RPM). Products produced from the process are separated between solid and liquid for analysis. Solid products were analyzed using Scanning Electron Microscopy (SEM), Particle Size Analysis (PSA), and Viscometer Ubbelohde. While liquid products were analyzed using UV-Vis Spectrophotometry with the DNS method. Based on the experimental results, HSM produced reducing sugar up to 0.1972 mg/mL. Granule breakage was also observed by SEM and increasing of the nanoscale granule.
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