Amylose Conformational Transitions in Binary DMSO/Water Mixtures

Starch structure and nutritional functionality - Past revelations and future prospects

Starch exists naturally as insoluble semi-crystalline granules assembled by amylose and amylopectin. Acknowledging the pioneers, we have reviewed the major accomplishments in the area of starch structure from the early 18th century and further established the relation of starch structure to nutritional functionality. Although a huge array of work is reported in the area, the review identified that some features of starch are still not fully understood and needs further elucidation. With the rise of diet-related diseases, it has never been more important to understand starch structure and use that knowledge to improve the nutritional value of the world's principal energy source.

NMR analysis and molecular dynamics conformation of α-1,6-linear and α-1,3-branched isomaltose oligomers as mimetics of α-1,6-linked dextran

The conformational preferences of several α-1,6-linear and α-1,3-branched isomalto-oligosaccharides were investigated by NMR and MD-simulations. Right-handed helical structure contributed to the solution geometry in isomaltotriose and isomaltotetraose with one nearly complete helix turn and stabilizing intramolecular hydrogen bonds in the latter by MD-simulation. Decreased helix contribution was observed in α-1,3-glucopyranosyl- and α-1,3-isomaltosyl-branched saccharide chains. Especially the latter modification was predicted to cause a more compact structure consistent with literature rheology measurements as well as with published dextranase-resistant α-1,3-branched oligosaccharides. The findings presented here are significant because they shed further light on the conformational preference of isomalto-oligosaccharides and provide possible help for the design of dextran-based drug delivery systems or for the targeted degradation of capsular polysaccharides by dextranases in multi-drug resistant bacteria.

Understanding Starch Structure: Recent Progress

Starch is a major food supply for humanity. It is produced in seeds, rhizomes, roots and tubers in the form of semi-crystalline granules with unique properties for each plant. Though the size and morphology of the granules is specific for each plant species, their internal structures have remarkably similar architecture, consisting of growth rings, blocklets, and crystalline and amorphous lamellae. The basic components of starch granules are two polyglucans, namely amylose and amylopectin. The molecular structure of amylose is comparatively simple as it consists of glucose residues connected through α-(1,4)-linkages to long chains with a few α-(1,6)-branches. Amylopectin, which is the major component, has the same basic structure, but it has considerably shorter chains and a lot of α-(1,6)-branches. This results in a very complex, three-dimensional structure, the nature of which remains uncertain. Several models of the amylopectin structure have been suggested through the years, and in this review two models are described, namely the “cluster model” and the “building block backbone model”. The structure of the starch granules is discussed in light of both models.

Computational study on the intramolecular self-organization of the macrorings of some ‘giant’ cyclodextrins (CDn, n = 40, 70, 85, 100)

A limited number of modes determine the overall deformations of the macrorings, which may have more than one cavity. Accordingly, they have the potential to accommodate more than one substrate molecule.

Effect of starch on the molecular mobility of amorphous sucrose

Molecular mobility in amorphous solid biomaterials is modulated by the composition and environment (primarily temperature). Phosphorescence of the triplet probe erythrosin B was used to generate a mobility map within amorphous sucrose films doped with starch ranging from 0.001 to 0.1 g starch/g sucrose. Data on the emission energy and lifetime of erythrosin B in sucrose and sucrose-starch films over the temperature range from 5 to 100 °C indicates that starch influences the molecular mobility as well as dynamic site heterogeneity of amorphous sucrose in a dose-dependent manner. At a starch/sucrose weight (wt) ratio below 0.005, both emission energy and lifetime decreased, and both the dipolar relaxation rate and nonradiative quenching rate k(TS0) increased, indicating that starch increased the matrix molecular mobility. At a ratio above 0.005, both emission energy and lifetime increased, and the dipolar relaxation rate and nonradiative quenching rate decreased, indicating that starch decreased the matrix mobility both in the glass and in the melt. The mobility showed a minimum value at a ratio of 0.01. The interactions existing in the sucrose-starch matrix are considered as the determining factor to influence the molecular mobility of sucrose-starch mixtures. Changes in the distribution of emission energies (emission bandwidth) and lifetimes indicated that starch increased the spectral heterogeneity at high contents while showing insignificant change or a slight decrease in the heterogeneity at low starch contents. These data illustrate the complex effects of a polymer with mainly linear structure and flexible conformation on the mobility of an amorphous, hydrogen bonded sugar matrix.

Free fatty acids electronically bridge the self-assembly of a three-component nanocomplex consisting of amylose, protein, and free fatty acids

The self-assembly of a ternary complex, which is formed through heating and cooling of a mixture of amylose (1.0 mg/mL), whey protein isolate (50 μg/mL), and free fatty acids (FFAs, 250 μg/mL) was investigated. High-performance size-exclusion chromatography-multi-angle laser light scattering (HPSEC-MALLS) analysis showed that the complex is a water-soluble supramolecule (Mw = 6-7 × 10(6)), with a radius of gyration of 20-100 nm, indicating a nanoscale complex. Experimental results using 1-monostearyl-rac-glycerol (MSG) or cetyl alcohol that is similar to FFA in structure (except the headgroup) indicate that FFAs are the bridge between thermodynamically incompatible amylose and protein molecules and their functional carboxyl group is essential to the formation of the complex. Additionally, the effects of pH and salt treatments suggest that electrostatic interactions between negatively charged carboxyl groups of FFAs and polyionic protein are the foundation for the self-assembly of the complex. The fact that FFA is one important component in the self-assembled complex with an estimated molar ratio of 6:1:192 (amylose/protein/FFA, ∼4-5% FFA) demonstrates that it might be used as a nanocarrier for the controlled release of lipophilic functional materials to maintain their stability, bioactivity, and more importantly water solubility.