Measuring mesoscopic scales in complex fluids embedded with giant cylindrical micelles with diffusing wave spectroscopy micro-rheology.

This review paper presents a procedure for measuring the mesoscopic scales in micellar solutions embedded with giant cylindrical micelles using the mean square displacement determined with a quasi-elastic multiple light scattering method (diffusing wave spectroscopy) and theory. The mesoscopic scales of interest are the micelles' total contour length, persistence and entanglement lengths, and the mesh size of the entangled micellar network. All of them depend on the physicochemical parameters of the solutions and determine the rheological behavior. We present an assessment of the whole procedure, the scattering experiments performance, the recovery of optical parameters, which includes dealing with the light absorption and its treatment, and how to develop the micro-rheology for obtaining the mesoscopic scales in these complex fluids.

Structural Changes in Wormlike Micelles on the Incorporation of Small Photoswitchable Molecules.

Chromophores susceptible to light-induced trans-cis isomerization embedded in cylindrical micelles can modify micelles and their light-responsive performance. A small chromophore (4-(phenylazo)benzoate ion) is embedded in cylindrical micelles made of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) in water. The microstructure is examined by scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). Rheological behavior and the length scales of the micellar network are determined by rheology and microrheology. The chromophore substantially modifies the micelles even without UV irradiation. The larger is the chromophore concentration, the smaller is the micellar length. Additional length scales of the micellar network do not substantially vary even when NaCl is added. Chromophore incorporation also modifies the rheology of the micellar solution, although gradient shear banding is preserved. Viscosity decreases as the chromophore concentration increases, and viscoelastic spectra are modified, but when they are correctly rescaled, they can be superimposed. The addition of the chromophore makes the fluids more Maxwellian, particularly when NaCl is also added. When the chromophore is incorporated into the micelles, there is a response after UV irradiation, although it does not produce a significant rheological change.

Morphological, structural, thermal, compositional, vibrational, and pasting characterization of white, yellow, and purple Arracacha Lego-like starches and flours (Arracacia xanthorrhiza).

This work is focused on the chemical, structural, morphological, thermal, IR vibrational, and pasting characterization of isolated white, yellow, and purple Arracacha starches from Colombia. Inductive couple plasma showed that these starches are rich in potassium. Scanning Electron Microscopy (SEM) images show that the starch granules are formed by ovoid fully filled Lego-like starch microparticles, the circular cross-section has a diameter between 9 and 15µm and mayor axis between 20 and 30µm. Each one of these ovoids is formed by irregular wedge-shaped 6 to 10 isolated starch granules with an average size between 4 and 12µm. The amylose content ranged between 31 and 36%. Arracacha starches exhibited high viscosity values (between 20.000 and 28.000cP), which could be influenced by the high content of potassium ions, due to the C-H~K Van Der Waals interaction that was identified by using IR spectroscopy. According to the X-ray diffraction analysis, the starch patterns exhibited broad diffracted peaks which could be associated with the existence of nano-crystals and lamellae; the Differential Scanning calorimetry (DSC) result showed starches with a low gelatinization temperature of about 60°C.

Physicochemical properties of nixtamalized corn flours with and without germ.

This research studied the influence of the germ components on the physicochemical properties of cooked corn and nixtamalized corn flours as a function of the calcium hydroxide content (from 0 to 2.1 w/w) and steeping time (between 0 and 9h). A linear relationship was found between calcium content in germ and steeping time used during nixtamalization process. X-ray diffraction analysis showed that calcium carbonate is formed into the germ structure to 2.1 w/w of calcium hydroxide and 9h steeping time. The presence of the germ improves the development of peak viscosity in flours, and it is related to the increases in calcium concentration in germ and the formation of amylose-lipid complexes. No significant changes were observed in palmitic, stearic, oleic and linoleic acids of corn oil. The levels of further corn oil deterioration were 2.1 w/w of calcium hydroxide concentration and 9h of steeping time.

Analysis of the pasting profile in corn starch: Structural, morphological, and thermal transformations, Part I.

This work is focused on the understanding of the apparent viscosity profile of corn starch, in terms of the physicochemical and morphological changes that take place during the thermal profile of starch-water suspension to its respective gel formation. A mathematical model was used to obtain the experimental operating conditions that satisfy the Froude number. Freeze drying samples are studied in different stages along the pasting profile. Changes in the structural properties of the samples are studied using X-ray diffraction, and the morphological changes are followed using scanning electron microscopy, differential scanning calorimetry was used to analyze the thermal changes in starch. The changes in the pasting profile are associated with structural, thermal,and morphological changes of the system and the analysis of the physicochemical transformation that occur during the pasting profile are explained. The finding in this work does not show evidence of gel retrogradation at the end of the cooling process.

Analysis of thermal pasting profile in corn starch rich in amylose and amylopectin: Physicochemical transformations, part II.

This work focused on the study of the behaviors of the apparent viscosity profiles of isolated corn starches rich in amylose and amylopectin, through the physicochemical and morphological changes that take place during the thermal profile and the gel formation. Frozen dry samples were studied at different stages along the pasting profile. Changes in the structural properties of the samples were studied using X-ray diffraction, and the morphological changes were followed using scanning electron microscopy, differential scanning calorimetry was used to analyze the thermal changes. The changes in the pasting profile (curve of apparent viscosity) were associated with structural, thermal, and morphological changes of the starch-water suspension. From the results obtained, a new interpretation of the parameters measured with the pasting profile is introduced. In this work does not show evidence of retrogradation at the end of the cooling process for starch rich in amylopectin and that starch rich in amylose does not develop viscosity.

Physicochemical, morphological, and rheological characterization of Xanthosoma robustum Lego-like starch.

This work presents the physicochemical and pasting characterization of isolated mafafa starch and mafafa flour (Xanthosoma robustum). According to SEM images of mafafa starches in the tuber, these starches form Lego-like shaped structures with diameters between 8 and 35 µm conformed by several starch granules of wedge shape that range from 2 to 7 µm. The isolated mafafa starch is characterized by its low contents of protein, fat, and ash. The starch content in isolated starch was found to be 88.58% while the amylose content obtained was 35.43%. X-ray diffraction studies confirm that isolated starch is composed mainly by amylopectin. These results were confirmed by differential scanning calorimetry and thermo gravimetric analysis. This is the first report of the molecular parameters for mafafa starch: molar mass that ranged between 2×10(8) and 4×10(8) g/mol, size (Rg) value between 279 and 295 nm, and molecular density value between 9.2 and 9.7 g/(mol nm(3)). This study indicates that mafafa starch shows long chains of amylopectin this fact contributes to higher viscosity development and higher gel stability. The obtained gel phase is transparent in the UV-vis region. The viscosity, gel stability and optical properties suggest that there is potential for mafafa starch applications in the food industry.