Characterization of Starch Using Flow Field-Flow Fractionation Techniques

Abstract: To improve the properties and functionality of starch, it is important to understand the physicochemical and structural characteristics as raw material, after being modified to increase its characteristics and/or during changes due to the processing conditions. For this reason, the objective of the present thesis is to improve the understanding of characteristics and molecular properties like molar mass (M), root-mean-square radius (rrms) and their relation to other physicochemical properties of starch extracted from different sources. Due to its complex structure, however, the analysis of starch can be challenging and few techniques are suitable. Nevertheless, some sub-techniques of the field-flow fractionation (FFF) family, especially asymmetric flow field-flow fractionation (AF4) have been shown to be appropriate for this task. Regarding the different FFF techniques, large-scale full-feed depletion mode of split flow thin cell fractionation (FFD-SF) was used as a preparative fractionation of corn and potato starch granules showing to be a useful technique for this task. In addition, the fractions obtained by large-scale FFD-SF were analyzed using optical microscopy (OM) and gravitational field-flow fractionation (GrFFF) which have been shown to be also suitable methods for determining the average size diameter (davg), with good agreement between these two techniques. Moreover, some slight improvements related to the analysis of starch as a polymer in solution using AF4 were made. First, with the use of a modified channel known as frit inlet (FI-AF4). It has been shown that almost double the amount of mass can be injected into the FI-AF4 channel in comparison with the conventional channel, without observing overloading effects. Second, the downturn phenomena that could be observed in the analysis of starch and/or other polymers, which is usually considered as an artifact that occurs during the analysis, was shown to be a result of co-elution of species with similar M but different conformation.Otherwise, physicochemical properties such as granule size, crystallinity, pasting properties among others as well as structural properties such as rrms, weight-average molar mass (Mw) and apparent density (ρapp) were analyzed in five different starches from Andean crops (three grains and two roots). To evaluate the relation between all these properties a statistical analysis was performed and a model was proposed that relates pasting properties i.e. peak viscosity and final viscosity with ρapp, gelatinization enthalpy, granule size and amylose content. Additionally, thermal properties were examined in relation to the granule size. For this, potato starch and its fractions (obtained using large-scale FFD-SF), as well as Andean roots, chosen for their similarity in botanical origin, were analyzed showing a correlation between enthalpy and granule size. Another factor affecting the thermal properties seems to be the amylose content.In the analysis of starch nanocomponents, it seems that the procedure used for obtaining non-solvent precipitated starch (non-SPS) resulted in new materials with amorphous structures that do not show particle characteristics when in solution, which suggests that designating these as nanoparticles might not be appropriate. Finally, in the analysis of starch extracted from different types of breads, the results show that M and size are affected by the baking process. In the case of breads, α-amylase enzyme was added. M and size decreased while the degree of branching (DB) and the number of reducing ends H-1(β-r) and H-1(α-r) increased. Furthermore, in starches extracted from Bolivian breads, it seems that the content of water during the preparation of the dough could affect the production of resistant starch.