Effect of branching of amylopectin on complexation with iodine as steric hindrance

Enhancing the anti-thixotropic properties of waxy maize starch modified by different α-amylases and its underlying molecular mechanism

The large thixotropy of the starch-thickened foods is often unfavorable in many applications. This study examined the contribution of the proportion of amylopectin chain length to time-dependence of starch gels. The α-amylase (AM) from Bacillus stearothermophilus and maltogenic α-amylase (MA) from Bacillus subtilis were used to trim amylopectin in different reaction patterns. HPLC, HPAEC and IBC data suggested AM attacked B-chains (DP 12-36), causing an increment in number of the chains with DP 6-12, whereas MA primarily trimmed the short B-chains (DP 12-18) and partial A-chains (DP 9-12) to generate short chains with DP 6-9. Interestingly, the recovery of AM-gels was faster than MA-gels at the same degree of hydrolysis when subjected to shear according to the linear correlation analysis. When releasing the same mass of sugar, shortening of the long internal chains played an important role in reducing time dependence of starch gel rather than the external side chains. Possible models were proposed to illustrate the differences in the mechanism of rapid-recovery caused by different side-chain distributions. The outcome provided a new perspective to regulate the thixotropy behavior of starch through enzyme strategies in the granular state.

The Iodine/Iodide/Starch Supramolecular Complex

The nature of the blue color in the iodine-starch reaction (or, in most cases, iodine-iodide-starch reaction, i.e., I2 as well as I- are typically present) has for decades elicited debate. The intensity of the color suggests a clear charge-transfer nature of the band at ~600 nm, and there is consensus regarding the fact that the hydrophobic interior of the amylose helix is the location where iodine binds. Three types of possible sources of charge transfer have been proposed: (1) chains of neutral I2 molecules, (2) chains of poly-iodine anions (complicated by the complex speciation of the I2-I- mixture), or (3) mixtures of I2 molecules and iodide or polyiodide anions. An extended literature review of the topic is provided here. According to the most recent data, the best candidate for the "blue complex" is an I2-I5--I2 unit, which is expected to occur in a repetitive manner inside the amylose helix.

On the Origin of the Blue Color in The Iodine/Iodide/Starch Supramolecular Complex

The nature of the blue color in the iodine-starch reaction is still a matter of debate. Some textbooks still invoke charge-transfer bands within a chain of neutral I₂ molecules inside the hydrophobic channel defined by the interior of the amylose helical structure. However, the consensus is that the interior of the helix is not altogether hydrophobic-and that a mixture of I₂ molecules and iodide anions reside there and are responsible for the intense charge-transfer bands that yield the blue color of the "iodine-starch complex". Indeed, iodide is a prerequisite of the reaction. However, some debate still exists regarding the nature of the iodine-iodine units inside the amylose helix. Species such as I₃^-, I₅^-, I₇^- etc. have been invoked. Here, we report UV-vis titration data and computational simulations using density functional theory (DFT) for the iodine/iodide chains as well as semiempirical (AM1, PM3) calculations of the amylose-iodine/iodide complexes, that (1) confirm that iodide is a pre-requisite for blue color formation in the iodine-starch system, (2) propose the nature of the complex to involve alternating sets of I₂ and I_x^- units, and (3) identify the nature of the charge-transfer bands as involving transfer from the I_x^- σ* orbitals (HOMO) to I₂ σ* LUMO orbitals. The best candidate for the "blue complex", based on DFT geometry optimizations and TD-DFT spectral simulations, is an I₂-I₅-I₂ unit, which is expected to occur in a repetitive manner inside the amylose helix.

Effects of Different Gluten Proteins on Starch’s Structural and Physicochemical Properties during Heating and Their Molecular Interactions

Starch–gluten interactions are affected by biopolymer type and processing. However, the differentiation mechanisms for gluten–starch interactions during heating have not been illuminated. The effects of glutens from two different wheat flours (a weak-gluten (Yangmai 22, Y22) and a medium-strong gluten (Yangmai 16, Y16)) on starch’s (S) structural and physicochemical properties during heating and their molecular interactions were investigated in this study. The results showed that gluten hindered the gelatinization and swelling of starch during heating when temperature was below 75 °C, due to competitive hydration and physical barriers of glutens, especially in Y22. Thus, over-heating caused the long-range molecular order and amylopectin branches of starch to be better preserved in the Y22-starch mixture (Y22-S) than in the Y16-starch mixture (Y16-S). Meanwhile, the starch’s degradation pattern during heating in turn influenced the polymerization of both glutens. During heating, residual amylopectin branching points restricted the aggregation and cross-linking of gluten proteins due to steric hindrance. More intense interaction between Y16 and starch during heating mitigated the steric hindrance in starch–gluten networks, which was due to more residual short-range ordered starch and hydrogen bonds involved in the formation of starch–gluten networks in Y16-S during heating.

Deciphering molecular interaction and digestibility in retrogradation of amylopectin gel networks

The impact of the internal part of aewx amylopectin on the gel network and digestibility during retrogradation was investigated using wx amylopectin as a reference. After β-amylolysis for 60 min (aewx-60), greater shifts in both λ_max value and absorbance of iodine binding profiles were observed, accompanied by an increment of short chains (DP 3-5) with reducing the external long chains (DP 17.2). For the amylopectin gels aged 7 days at 4 °C, aewx had greater intermolecular aggregation of double helices to form junction zones, resulting in remarkably higher G', which was significantly greater than that of wx amylopectin or aewx-60. Moreover, aewx amylopectin had a greater RS accompanied by a reduction in RDS after retrogradation. The gel network models of retrograded amylopectins were built to interpret more molecular interactions for aewx than those of wx. The results revealed that aewx amylopectin with a higher proportion of longer external chains prompted the flexibility to align and interact for the formation of double helices and enzyme-resistant structures.

Complexation of Amylosucrase-Modified Waxy Corn Starch with Fatty Acids: Determination of Their Physicochemical Properties and Digestibilities

In this study, starch-lipid complexes were prepared using normal corn starch (NC) and amylosucrase-modified waxy corn starch (ASWC) with myristic acid (C14:0) and palmitic acid (C16:0). The amylosucrase modification elongated branch chains in waxy corn starch leading to an increase of apparent amylose content (29.7%) similar to that of NC (29.0%). The X-ray diffraction of starch-lipid complexes revealed a V-type pattern, a clear indication of complex formation. The ability of the ASWC to complex with fatty acids was greater than that of NC. Interestingly, the changes in relative crystallinity, thermal parameters, and digestion properties according to the complexation showed opposite patterns in NC and ASWC. This study found that the structure of ASWC contributes to the formation of starch-fatty acid complexes and suggested that the ASWC can be preferred over NC in a delivery system. PRACTICAL APPLICATION: Amylopectin has been considered to be incapable of forming complexes with fatty acids due to its short chain length and steric hindrance. Through this study, an appropriate enzymatic modification of the molecular structures of waxy starches could make a complexation of waxy starches with fatty acids possible. The findings of this study suggest a promising perspective for utilization of waxy starch as a carrier material of lipophilic molecules.

Brain Glycogen Structure and Its Associated Proteins: Past, Present and Future

This chapter reviews the history of glycogen-related research and discusses in detail the structure, regulation, chemical properties and subcellular distribution of glycogen and its associated proteins, with particular focus on these aspects in brain tissue.

Preparation and characterization of the inclusion complexes between amylosucrase-treated waxy starch and palmitic acid

Amylosucrase-treated waxy corn starch (AS) was produced to extend the chain length of amylopectin to a great extent in comparison to its native chain length. An amylopectin-palmitic acid (PA) complex was prepared by heat-treating (121°C) a starch/PA mixture and its subsequent further incubation (95°C, 24 h); moreover, its structure and digestibility were studied. Unmodified waxy starch could not complex at all, whereas elongation due to amylosucrase modification allowed amylopectin to form a complex with PA to a small extent. Complexation between AS and PA caused a decrease in relative crystallinity. The AS-PA complex displayed an endothermic peak representing type I inclusion complexes rather than type II complexes. The formation of complexes did not significantly affect the in vitro digestibility maintaining the low digestibility of AS resulting from extremely small amounts of complexes and the type of complex.

Molecular iodine/polymer complexes

A unique feature of molecular iodine by far, is its ability to bind to polymeric materials. A plethora of natural and synthetic polymers develop complexes when treated with molecular iodine, or with a mixture of molecular iodine and potassium iodide. Many unexpected findings have been encountered upon complexation of iodine and the polymer skeleton, including the color formation, the polymer morphology changes, the complexation sites or regions, the biological activity, and the electrical conductivity enhancement of the complexes, with polyiodides (In¯), mainly I3¯ and I5¯, as the actual binding species. Natural polymers that afford such complexes with iodine species are starch (amylose and amylopectin), chitosan, glycogen, silk, wool, albumin, cellulose, xylan, and natural rubber; iodine-starch being the oldest iodine-natural polymer complex. By contrast, numerous synthetic polymers are prone to make complexes, including poly(vinyl alcohol) (PVA), poly(vinyl pyrrolidone) (PVP), nylons, poly(Schiff base)s, polyaniline, unsaturated polyhydrocarbons (carbon nanotubes, fullerenes C60/C70, polyacetylene; iodine-PVA being the oldest iodine-synthetic polymer complex.

Reversibility and hierarchy of thermal transition of hen egg-white lysozyme studied by small-angle x-ray scattering

To clarify mechanisms of folding and unfolding of proteins, many studies of thermal denaturation of proteins have been carried out at low protein concentrations because in many cases thermal denaturation accompanies a great tendency of aggregation. As small-angle x-ray scattering (SAXS) measurements are liable to use low-concentration solutions of proteins to avoid aggregation, SAXS has been regarded as very difficult to observe detailed features of thermal structural transitions such as intramolecular structural changes. By using synchrotron radiation SAXS, we have found that the presence of repulsive interparticle interaction between proteins can maintain solute particles separately to prevent further aggregation in thermal denaturation processes and that under such conditions the thermal structural transition of hen egg-white lysozyme (HEWL) holds high reversibility even at 5% w/v HEWL below pH approximately 5. Because of the use of the high concentration of the solutions, the scattering data has enough high-statistical accuracy to discuss the thermal structural transition depending on the structural hierarchy. Thus, the tertiary structural change of HEWL starts from mostly the onset temperature determined by the differential scanning calorimetry measurement, which accompanies a large heat absorption, whereas the intramolecular structural change, corresponding to the interdomain correlation and polypeptide chain arrangement, starts much prior to the above main transition. The present finding of the reversible thermal structural transitions at the high protein concentration is expected to enable us to analyze multiplicity of folding and unfolding processes of proteins in thermal structural transitions.