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.

Gelatinized and nongelatinized starch/pp blends: effect of starch source and carboxylic and incorporation

“…However, for blends with acids, less quantity of energy was consumed and the starch maintained its granule structure. These results corroborated the literature data, where is possible perceive that a higher torque is required for destruction/melting of starch particles [4]. Also, as already discussed, acids act also as aid processing agent, lowing the shear stresses, which might be not enough to destroy the starch granules.…”

“…This behavior was attributed to the higher phosphorus content on potato starch [39,58]. Castaño et al [4] demonstrated that phosphorus content influences starch plasticization in shear, where the repulsion between phosphate groups facilities the diffusion of plasticizer into starch chains, changing starch-paste viscosity. Probably, this effect also explains the higher elongation at break values for potato blends with C18 (Table 1) rather than C14, once stearic acid (C18) has higher molar mass.…”

“…where N is the rotation speed (rpm), m is the total sample mass (g), t is the processing time (min) and C(t) is the total torque produced during the processing time (Nm). The SME was expressed in kJ/kg [4,35].…”

“…Due to the strong intermolecular interactions, the starch undergoes decomposition before melting, making it difficult to use in some temperature ranges in the processing. However, this can be improved upon the disruption of the granule which occurs when the starch granules are heated in the presence of a plasticizer, such as water, glycerol or polyvinyl alcohol (PVA) [3][4][5]. This thermoplastic starch is well-known as TPS [6].…”

Effect of Moisture Content on Structure and Properties of Fried Potato Starch

“…The repulsion between phosphate groups made it easier to disrupt the amylopectin‐amylopectin hydrogen bonds in the double helices and destroy the crystalline of starch. Therefore, the ordered structure of starch granules with low phosphorus content was less disrupted . Starch‐bound phosphate played an important role in determining the starch viscosity characteristics.…”