Application of small-angle neutron scattering to the study of the structure of starch granules

Acceleration mechanism of the rehydration process of dried rice noodles by the porous structure

Rehydration of dried rice noodles (DRNs) is a time-consuming process, which is dominated by the compactness of noodle structure. Therefore, DRNs with differentiated porous structures were prepared, and their effect on the rehydration process was investigated. Porous structure can shorten rehydration time by reducing the time needed for water to migrate into the noodle core, or the water amount required for rehydration. Magnetic resonance imaging showed that although larger pores facilitate absorbing more water, the time for water to migrate into the noodle center is longer than that of medium size pores, as water needs to fill the periphery large hole before inward migration. SAXS analysis demonstrated that the presence of flexible starch molecular chains reduce the water required to achieve the maximum tensile strain of samples, thus shortening the rehydration time. Understanding the acceleration mechanism of porous structure on rehydration contributes to designing improved process of instant noodle products.

Microstructures of Starch Granules with Different Amylose Contents and Allomorphs as Revealed by Scattering Techniques

In this study, as-is (ca. 12% moisture by mass) and hydrated (50% water by mass) granules of waxy potato (WP), waxy wheat (WW), waxy maize, normal maize, and high-amylose maize (HAM) starches were investigated by using small-angle neutron and X-ray scattering (SANS and SAXS), wide-angle X-ray scattering, and ultra-small-angle neutron scattering. The SANS and SAXS data were fitted using the two-phase stacking model of alternating crystalline and amorphous layers. The partial crystalline lamellar structures inside the growth rings of granules were analyzed based on the inter-lamellar distances, thicknesses of the crystalline lamellae and amorphous layers, thickness polydispersities, and water content in each type of layer. Despite having a longer average chain length of amylopectin, the WP and HAM starches, which had B-type allomorph, had a shorter inter-lamellar distance than the other three starches with A-type allomorph. The WP starch had the most uniform crystalline lamellar thickness. After hydration, the amorphous layers were expanded, resulting in an increase of inter-layer distance. The low-angle intensity upturn in SANS and SAXS was attributed to scattering from interfaces/surfaces of larger structures, such as growth rings and macroscopic granule surfaces. Data analysis methods based on model fitting and 1D correlation function were compared. The study emphasized─owing to inherent packing disorder inside granules─that a comprehensive analysis of different parameters was essential in correlating the microstructures with starch properties.

An alternative analysis of contrast-variation neutron scattering data of casein micelles in semi-deuterated milk

Contrast-variation small-angle neutron scattering (CV-SANS) is an excellent way to determine the structure of complex, hierarchical colloids, including self-assembled biological systems. In these experiments, the scattering length density of solvents is changed (by varying the ratio of water or [Formula: see text] and heavy water or [Formula: see text]) to highlight or mask scattering from different components in the system. This approach has been used with synthetic colloids, but it is also increasingly being used in the biological and food sciences. Perhaps the most studied food colloid is the "casein micelle," a self-assembled nanometer-scale colloid of the structure-forming casein protein in milk. CV-SANS data available in the literature are typically analyzed using approximations, which may be invalid for casein micelles, as they have been shown to be sticky spheres. To assess the applicability of this approximate approach, a comprehensive set of CV-SANS data from casein micelles in diluted milk was reanalyzed using a model-based approach, where the casein micelles were formally treated as interacting spheres. In general, the conclusions of the previous study are reproduced, but this new approach makes it more straightforward to distinguish the different components in milk and can be applied to any dairy sample with known form of interparticle interactions, which offers the possibility of studying semi-deuterated milk at its native concentration.

Kinetics of structural reorganizations in multilamellar photosynthetic membranes monitored by small-angle neutron scattering

We demonstrate the power of time-resolved small-angle neutron scattering experiments for the investigation of the structure and structural reorganizations of multilamellar photosynthetic membranes. In addition to briefly summarizing our results on thylakoid membranes isolated from higher plants and in unicellular organisms, we discuss the advantages and technical and methodological limitations of time-resolved SANS. We present a detailed and more systematical investigation of the kinetics of light-induced structural reorganizations in isolated spinach thylakoid membranes, which show how changes in the repeat distance and in the long-range order of the multilamellar membranes can be followed with a time resolution of seconds. We also present data from comparative measurements performed on thylakoid membranes isolated from tobacco.

Characterization Methods for Starch-Based Materials: State of the Art and Perspectives

Improving starch-containing materials, whether food, animal feed, high-tech biomaterials, or engineering plastics, is best done by understanding how biosynthetic processes and any subsequent processing control starch structure, and how this structure controls functional properties. Starch structural characterization is central to this. This review examines how information on the three basic levels of the complex multi-scale structure of starch – individual chains, the branching structure of isolated molecules, and the way these molecules form various crystalline and amorphous arrangements – can be obtained from experiment. The techniques include fluorophore-assisted carbohydrate electrophoresis, multiple-detector size-exclusion chromatography, and various scattering techniques (light, X-ray, and neutron). Some examples are also given to show how these data provide mechanistic insight into how biosynthetic processes control the structure and how the various structural levels control functional properties.

High-Pressure Potato Starch Granule Gelatinization: Synchrotron Radiation Micro-SAXS/WAXS Using a Diamond Anvil Cell

Potato starch granules have been examined by synchrotron radiation small- and wide-angle scattering in a diamond anvil cell (DAC) up to 750 MPa. Use of a 1 microm synchrotron radiation beam allowed the mapping of individual granules at several pressure levels. The data collected at 183 MPa show an increase in the a axis and lamellar period from the edge to the center of the granule, probably due to a gradient in water content of the crystalline and amorphous lamellae. The average granules radius increases up to the onset of gelatinization at about 500 MPa, but the a axis and the lamellar periodicity remain constant or even show a decrease, suggesting an initial hydration of amorphous growth rings. The onset of gelatinization is accompanied by (i) an increase in the average a axis and lamellar periodicity, (ii) the appearance of an equatorial SAXS streak, and (iii) additional short-range order peaks.

A Method for Estimating the Nature and Relative Proportions of Amorphous, Single, and Double-Helical Components in Starch Granules by 13C CP/MAS NMR

An improved method to analyze the (13)C NMR spectra of native starches, which considers the contribution of the V-type conformation and the nature of the amorphous component, has been developed. Starch spectra are separated into amorphous and ordered subspectra, using intensity at 84 ppm as a reference point. The ordered subspectra of high amylose starches show the presence of both V-type single helices and B-type double helices. Relative proportions of amorphous, single, and double-helical conformations are estimated by apportioning intensity of C1 peak areas between conformational types on the basis of ordered and amorphous subspectra of the native starch. Quantitative analysis shows that the V-type single-helical component increases with amylose content of starches. Different amorphous subspectra are needed to provide a consistent analysis of granular starches from diverse sources. The method of preparation was found to be more important than the starch botanical origin in determining (13)C NMR spectral features of amorphous samples.

Use of (13)c MAS NMR to study domain structure and dynamics of polysaccharides in the native starch granules

To investigate the domain structure and dynamics of polysaccharides in the native starch granules, a variety of high resolution, solid-state (13)C NMR techniques have been applied to all three (A-, B-, and C-) types of starch with different water content. Both single-pulse-excitation magic-angle-spinning (SPEMAS) and cross-polarization-magic-angle-spinning (CPMAS) methods have been employed together with the PRISE (proton relaxation induced spectral-editing) techniques to distinguish polysaccharide fractions in different domains and having distinct dynamics. It has been found that, for all three types of dry starch granules, there are two sets of NMR signals corresponding to two distinct ordered polysaccharides. Hydration leads to substantial mobilization of the polysaccharides in the amorphous regions, but no fundamental changes in the rigidity of the polysaccharides in the crystalline (double) helices. Full hydration also leads to limited mobility changes to the polysaccharides in the amorphous lamellae (branching zone) within the amylopectin clusters and in the gaps between the arrays of the amylopectin clusters. Under magic-angle spinning, proton relaxation-time measurements showed a single component for T(1), two components for T(1rho), and three components for T(2). PRISE experiments permitted the neat separation of the (13)C resonances of polysaccharides in the crystalline lamellae from those in the amorphous lamellae and the amylose in the gaps between amylopectin clusters. It has been found that the long (1)H T(1rho) component ( approximately 30 ms) is associated with polysaccharides in the crystalline lamellae in the form of double helices, whereas the short T(1rho) component (2-4 ms) is associated with amylose in the gaps between amylopectin clusters. The short (1)H T(2) component ( approximately 14 micros) is associated with polysaccharides in the crystalline lamellae; the intermediate component (300-400 micros) is associated with polysaccharides in the amorphous lamellae and amylose in the gaps between amylopectin clusters. The long T(2) component is associated with both mobile starch protons and the residue water protons.

An improved model for analyzing the small angle x-ray scattering of starch granules

The structure of starch was studied using small-angle x-ray scattering (SAXS). The scattering data was modeled by considering a finite stack of alternating lamellae that are allowed to fluctuate both along the layer repeat direction and along the transverse layer direction. Analysis in this way of the SAXS data from starch allowed fresh insights into the native structure of several starch species, particularly potato starch. The novel model presented in this work was able to capture the experimentally observed SAXS patterns much better than previous models, which did not incorporate transverse layer fluctuations.

NMR local range investigations in amorphous starchy substrates: II-Dynamical heterogeneity probed by (1)H/(13)C magnetization transfer and 2D WISE solid state NMR

In the preceding paper, we have investigated the structural heterogeneous character of a series of amorphous samples prepared from various starchy substrates (native potato starch, amylopectin and amylose) following different techniques of preparation (casting, freeze drying and solvent exchange). Spectral decompositions of the C1 resonances of the (13)C CP-MAS (Cross Polarization and Magic Angle Spinning) spectra under (1)H decoupling have shown the existence of five main types of alpha(1-4) linkages. In this part, 2D solid state NMR WISE experiments and the (13)C/(1)H magnetization transfer in CP as a local probe for both structures and dynamics were used. The (13)C CP magnetization curves versus contact time of each C1 component in each recorded spectrum were fitted with an analytic function taking into account two (1)H reservoirs. Interpretation of the characteristic times derived from fitting yields some improvements on the knowledge of the heterogeneity of the samples and on the water molecules distribution.

SANS study of the distribution of water within starch granules

This study describes contrast variation small angle neutron scattering (SANS) experiments which focus on the role which the intra-granular room temperature distribution of water and carbohydrate plays in determining the native structure and subsequent functionality of starch. It is shown that variations in botanical origin and amylose content do not correlate with significant differences in room temperature composition of A-type starch granules. In turn, variations in the gelatinisation behaviour of A-type starches do not correlate with variations in room temperature water distribution. In contrast, the room temperature water content is found to differ significantly between granules of potato (B-type) and a range of A-type starch cultivars. A correlation is found between these compositional differences and variations in crystal structure, which has implications for biological growth conditions and gelatinisation behaviour.