Morphological and structural changes of starch during processing by melt blending

Abstract

The morphological and structural changes of the granule architecture of normal starch during the melt blending in a batch mixer were investigated. Native potato, maize, and chestnut starch with different crystal structures were used as raw materials. Samples obtained at different times of melt blending were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and polarized light (PL) microscopy techniques. The variation of torque versus time depended on the starch type; the thermo-plasticization of potato starch (B-type) occurred in two steps, whereas that of maize (A-type) and chestnut (C-type) starches took place in one step. An enhancement of the thermo-plasticization after 15 min of starch processing was not observed by SEM and PL microscopy. However, the potato starch with longer amylopectin chains and higher phosphorus content presented a higher extent of destructurization when compared with the maize and chestnut starches. The XRD patterns of the plasticized starch samples showed residual and V-type induced crystallinity, corroborating the partial thermo-plasticization of starches. The extent of thermo-plasticization depended on the crystallinity type and phosphorus content of normal starch.