13C-N.M.R. study of the conformation of helical complexes of amylodextrin and of amylose in solution

Structural properties of the intra- and interhelical cavities of V6-type crystalline starches

V-type crystalline starch is known for its property to enhance aroma retention. Intra- and interhelical cavities are the first-order characteristics of V-type crystalline starch, which can affect its properties from microscopic level. This work aims to provide a detailed analysis of structural attributes of intra- and interhelical cavities and their influence on the properties of V-type crystalline starches. Helix deformation was caused due to the formation of interhelical cavities, which was reflected by the downfield shift of the signals for C1 and C4 as well as the appearance of an independent signal for C3 in 13C CP/MAS NMR spectra. Unit cell and lamellar structure formed by the aggregation of intrahelical cavities exhibited relatively low cell volume and high fractal dimension at crystal cell and lamellar levels. Toward a larger crystal, d-spacing increased with the formation of interhelical cavities, causing low-angle shifts of V-type crystalline starches in X-ray diffraction profiles. Intrahelical cavities enabled V6I-type crystalline starch to show high crystallinity per unit volume and a favorable short-range order, contributing greatly to the stable thermal properties. The flavor quality improvement in starch-based food is attributed to the structural characteristics of helical cavities and their relationship with the properties of V-type crystalline starches.

Multi-Scale Structural Insights into Enzymatically Hydrolyzed Lentil Starch Concentrates Prepared by In Vitro Method Using Different Types of Enzymes

This study was undertaken to investigate the enzymatic hydrolysis of lentil starch concentrates from conventional cooked seeds (CCLSC) by the action of different types of enzymes, including pancreatin (PC-EHSC), heat-stable α-amylase (HS-EHSC), β-amylase (βA-EHSC), amyloglucosidase (AMG-EHSC), and multi-enzymes (βA-HS-AMG-EHSC); their multi-scale structural characteristics of the enzymatic hydrolysis products of lentil starch concentrates were compared. The morphological features distinguished among different samples. The Fourier-transform infrared spectroscopy and solid-state ¹³C CP/MAS NMR spectral features indicated the possible formation of a binary and ternary complex among amylose, protein and lipids. The X-ray diffraction results revealed that the V-type characteristic diffraction peaks were more obvious for samples including PC-EHSC and βA-EHSC, which was in line with their lowest polydispersity index (DP_n). PC-EHSC and βA-EHSC also showed an increased peak intensity of the scattering maximum on the small-angle X-ray scattering spectra, whereas CCLSC exhibited an overall lower peak intensity within the studied q range of scattering. The highest XRD crystallinity and the lowest DP_n value obtained for PC-EHSC indicated that the starch polymers modified by pancreatin could produce glucan chains with a comparatively homogenous M_w distribution that are readily recrystallized by hydrogen bonding through chain aggregation. Comparatively, the lowest relative crystallinity for HS-EHSC obtained from XRD suggested that thermostable α-amylolysis was unfavorable for the formation of starch structure with a higher degree of molecular order. This study could provide useful information for the needed research to obtain a deeper understanding of the impact of different amylolysis actions on the structural organization of starch hydrolysates and to provide a theoretical foundation for the development of fermentable enzymatically hydrolyzed starch with well-tailored physiological properties.

Starch-lipid interaction alters the molecular structure and ultimate starch bioavailability: A comprehensive review

Starch bioavailability which results in eliciting postprandial glycaemic response, is a trait of great significance and is majorly influenced by the physical interaction among the matrix components governed by their molecular structure as well as dynamics. Among physical interactions limiting starch bioavailability, starch and any guest molecules like lipid interact together to alter the molecular structure into a compact V-type arrangement endorsing the processed crystallinity, thus limiting carbolytic enzymatic digestion and further bioavailability. Considering the importance of starch-lipid dynamics affecting bioavailability, intensive research based on endogenous (internal lipids which are embedded into the food matrix) as well as exogenous (those are added from outside into the food matrix during processing like cooking) lipids have been carried out, endorsing physical interactions at colloidal and microstructural levels. The shared insights on such binary (starch-lipid) interactions revealed the evolution of characterization techniques as well as their role on altering the functional and nutritional value. It is very much vital to have a thorough understanding about the mechanisms on the molecular level to make use of these matrix interactions in the most efficient way, while certain basic questions are still remaining unaddressed. Do starch - lipid complexation affects the ultimate starch bioavailability? If so, then whether such complexation ability depends on amylose - fatty acid/lipid content? Whether the complexation is influenced further by fatty acid type/concentration/chain length or saturation? Further comprehending this, whether the altered bioavailability by binary (starch-lipid) could further be affected by ternary (starch-lipid-protein) and quaternary (starch-lipid-protein-phenolics) interactions are also discussed in this comprehensive review.

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.

Preparation of amylose-poly(methyl methacrylate) inclusion complex as a smart nanocarrier with switchable surface hydrophilicity

Amylose, as a linear biopolymer, tends to form helical inclusion complexes with suitable guest species. This is of great importance for a variety of applications, especially in the pharmaceutical and food industry. In this study, we propose an approach for the preparation of a novel inclusion complex with switchable surface hydrophilicity. For this purpose, amylose was first conjugated to ethylene diamine hydrophilic residues. Then, the short chains of the hydrophobic poly(methyl methacrylate, PMMA) were grafted onto the cavity of amylose through atom transfer radical polymerization (ATRP). According to CD spectroscopy results, the amylose-PMMA inclusion complexes displayed solvent-directed helical chirality inversion using either DMSO or water as a solvent. Fluorescence imaging, AFM and DLS techniques revealed the solvent-dependent surface hydrophilicity of the amylose-PMMA inclusion complex. Interestingly, its morphological studies displayed a central cavity, which makes it suitable for carrying cargoes in drug delivery applications. Obtaining the amylose-polymer inclusion complexes with tailorable hydrophilicity of both the exterior surface and the interior cavity can be of paramount importance for a wide variety of bio-applications.

Applications of nuclear magnetic resonance spectroscopy for the understanding of enantiomer separation mechanisms in capillary electrophoresis

This review deals with the applications of nuclear magnetic resonance (NMR) spectroscopy to understand the mechanisms of chiral separation in capillary electrophoresis (CE). It is accepted that changes observed in the separation process, including the reversal of enantiomer migration order (EMO), can be caused by subtle modifications in the molecular recognition mechanisms between enantiomer and chiral selector. These modifications may imply minor structural differences in those selector-selectand complexes that arise from the above mentioned interactions. Therefore, it is mandatory to understand the fine intermolecular interactions between analytes and chiral selectors. In other words, it is necessary to know in detail the structures of the complexes formed by the enantiomer (selectand) and the selector. Any differences in the structures of these complexes arising from either enantiomer should be detected, so that enantiomeric bias in the separation process could be explained. As to the nature of these interactions, those have been extensively reviewed, and it is not intended to be discussed here. These interactions contemplate ionic, ion-dipole and dipole-dipole interactions, hydrogen bonding, van der Waals forces, π-π stacking, steric and hydrophobic interactions. The main subject of this review is to describe how NMR spectroscopy helps to gain insight into the non-covalent intermolecular interactions between selector and selectand that lead to enantiomer separation by CE. Examples in which diastereomeric species are created by covalent (irreversible) derivatization will not be considered here. This review is structured upon the different structural classes of chiral selectors employed in CE, in which NMR spectroscopy has made substantial contributions to rationalize the observed enantioseparations. Cases in which other techniques complement NMR spectroscopic data are also mentioned.

Evaluation of sulfated maltodextrin as a novel anionic chiral selector for the enantioseparation of basic chiral drugs by capillary electrophoresis

Introducing a new class of chiral selectors is an interesting work and this issue is still one of the hot topics in separation science and chirality. In this study, for the first time, sulfated maltodextrin (MD) was synthesized as a new anionic chiral selector and then it was successfully applied for the enantioseparation of five basic drugs (amlodipine, hydroxyzine, fluoxetine, tolterodine, and tramadol) as model chiral compounds using CE. This chiral selector has two recognition sites: a helical structure and a sulfated group which contribute to three corresponding driving forces; inclusion complexation, electrostatic interaction, and hydrogen binding. Under the optimized condition (buffer solution: 50 mM phosphate (pH 3.0) and 2% w/v sulfated MD; applied voltage: 18 kV; temperature: 20°C), baseline enantioseparation was observed for all mentioned chiral drugs. When instead of sulfated MD neutral MD was used under the same condition, no enantioseparation was observed which means the resolution power of sulfated MD is higher than neutral MD due to the electrostatic interaction between sulfated groups and protonated chiral drugs. Also, the countercurrent mobility of negatively charged MD (sulfated MD) allows more interactions between the chiral selector and chiral drugs and this in turn results in a successful resolution for the enantiomers. Furthermore, a higher concentration of neutral MD (approximately five times) is necessary to achieve the equivalent resolution compared with the negatively charged MD.

Maltodextrins as chiral selectors in CE: molecular structure effect of basic chiral compounds on the enantioseparation

Prediction of chiral separation for a compound using a chiral selector is an interesting and debatable work. For this purpose, in this study 23 chiral basic drugs with different chemical structures were selected as model solutes and the influence of their chemical structures on the enantioseparation in the presence of maltodextrin (MD) as chiral selector was investigated. For chiral separation, a 100-mM phosphate buffer solution (pH 3.0) containing 10% (w/v) MD with dextrose equivalent (DE) of 4-7 as chiral selector at the temperature of 25°C and voltage of 20 kV was used. Under this condition, baseline separation was achieved for nine chiral compounds and partial separation was obtained for another six chiral compounds while no enantioseparation was obtained for the remaining eight compounds. The results showed that the existence of at least two aromatic rings or cycloalkanes and an oxygen or nitrogen atom or -CN group directly bonded to the chiral center are necessary for baseline separation. With the obtained results in this study, chiral separation of a chiral compound can be estimated with MD-modified capillary electrophoresis before analysis. This prediction will minimize the number of preliminary experiments required to resolve enantiomers and will save time and cost.

Effects of lipids on enzymatic hydrolysis and physical properties of starch

This study aimed to understand effects of lipids, including corn oil (CO), soy lecithin (SL), palmitic acid (PA), stearic acid (SA), oleic acid (OA), and linoleic acid (LA), on the enzymatic hydrolysis and physical properties of normal corn (NCS), tapioca (TPS), waxy corn (WCS), and high-amylose corn (HA7) starch, and to elucidate mechanisms of interactions between the starches and lipids. After cooking with the lipids (10%, w/w, dsb), NCS, TPS, and HA7 showed significant decreases in enzymatic hydrolysis, and their DSC thermograms displayed amylose-lipid-complex dissociation peaks except with the CO. (13)C NMR spectra of amylodextrin with CO showed downfield changes in the chemical shifts of carbons 1 and 4 of the anhydroglucose unit, indicating helical complex formation. Generally, free fatty acids (FFAs) reduced, but SL increased the peak viscosities of starches. FFAs and SL decreased, but CO increased the gel strength of NCS. These lipids displayed little impacts on the enzymatic hydrolysis and physical properties of WCS because it lacked amylose.

Effect of surfactant type on surfactant-maltodextrin interactions: isothermal titration calorimetry, surface tensiometry, and ultrasonic velocimetry study

Isothermal titration calorimetry (ITC), surface tensiometry, and ultrasonic velocimetry were used to characterize surfactant-maltodextrin interactions in buffer solutions (pH 7.0, 10 mM NaCl, 20 mM Trizma base, 30.0 degrees C). Experiments were carried out using three surfactants with similar nonpolar tail groups (C12) but different charged headgroups: anionic (sodium dodecyl sulfate, SDS), cationic (dodecyl trimethylammonium bromide, DTAB), and nonionic (polyoxyethylene 23 lauryl ether, Brij35). All three surfactants bound to maltodextrin, with the binding characteristics depending on whether the surfactant headgroup was ionic or nonionic. The amounts of surfactant bound to 0.5% w/v maltodextrin (DE 5) at saturation were < 0.3 mM Brij35, approximately 1-1.6 mM SDS, and approximately 1.5 mM DTAB. ITC measurements indicated that surfactant binding to maltodextrin was exothermic. Surface tension measurements indicated that the DTAB-maltodextrin complex was more surface active than DTAB alone but that SDS- and Brij35- maltodextrin complexes were less surface active than the surfactants alone.

Two-dimensional rotating-frame Overhauser spectroscopy (ROESY) and 13C NMR study of the interactions between maltodextrin and an anionic surfactant

Rotational frame nuclear Overhauser effect spectroscopy (ROESY) and (13)C NMR measurements were carried out to study the molecular interaction between maltodextrin, a digestive byproduct of starch, and an anionic surfactant. Significant differences in chemical shifts were observed when sodium dodecyl sulfate (SDS) was introduced into the maltodextrin (DE 10) solutions. (13)C NMR measurement indicated that there were downfield shifts and broadening of peaks, especially in the region of 75-81 and 100-103 ppm, which were assigned to carbons 1 and 4 of the d-glucopyranose residues of maltodextrin, respectively. ROESY spectra indicated cross-peaks between the SDS and maltodextrin protons. These peaks can arise only in the case of the designated SDS protons and maltodextrin protons being less than 0.5 nm apart for a substantial period of time. The most intense cross-peaks are those between the central CH(2) protons of SDS near 1.2 ppm and the maltodextrin protons ranging from 3.5 to 3.9 ppm. The SDS-H3 CH(2) protons were resolved from the bulk of the SDS protons, with peaks and shoulders at 1.25 ppm, which indicated an especially strong interaction of the SDS hydrophobic tail with MD6 and some less intense interactions with MD2, 4, and 5.

A functional raw starch-binding domain of barley alpha-amylase expressed in Escherichia coli

The mature form of barley seed low-pI alpha-amylase (BAA1) possesses a raw starch-binding site in addition to the catalytic site. A truncated cDNA encoding the C-terminal region (aa 281-414) and containing the proposed raw starch-binding domain (SBD) but lacking Trp278/Trp279, a previously proposed starch granule-binding site, was synthesized via PCR and expressed in Escherichia coli as an N-terminal His-Tag fusion protein. SBD was produced in the form of insoluble inclusion bodies that were extracted with urea and successfully refolded into a soluble form via dialysis. To determine binding, SBD was purified by affinity chromatography with cycloheptaamylose as ligand cross-linked to Sepharose. This work demonstrates that a SBD is located in the C-terminal region and retains sufficient function in the absence of the N-terminal, catalytic, and Trp278/279 regions.

Isolation of a raw starch-binding fragment from barley alpha-amylase

Barley alpha-amylase was purified by ammonium sulfate fraction, ion-exchange, ultrafiltration, and gel filtration to homogeneity. The purified enzyme was partially digested with trypsin, and the reaction mixture was applied to a cyclohepta-amylose epoxy Sepharose 6B column. Bound fragments were eluted by free cyclohepta-amylose, lyophilized, and separated on Tricine gels. Four fragments were shown to interact with beta-cyclodextrin. The fragment that could be identified on the gel with the lowest molecular weight (11 kDa) was electroblotted onto PVDF membrane for sequencing. The N-terminal sequence of this fragment was determined with the N-terminal amino acid corresponding to Ala283 in the whole protein. The trypsin cleavage was at Lys282/Ala283 and the C-terminal cleavage occurred at Lys354/Ile355 to give a fragment size of 11 kDa as estimated by SDS-PAGE. The fragment would be located at the C-terminal region, forming a majority of the antiparallel beta-sheets in domain C and the alpha7- and alpha8-helices of the (alpha/beta)8 domain.

Review: cyclodextrins and their interaction with amylolytic enzymes

This review is concerned with inhibition of amylases by cyclodextrins (cyclic maltooligosaccharides), the interaction that occurs between amylases and cyclodextrins and the application of cyclodextrin affinity chromatography in the purification of amylases. In many cases, amylases that are competitively inhibited by cyclodextrins can be purified by cyclodextrin affinity chromatography with the cyclodextrins interacting with the active site on such enzymes. Interestingly amylases that are not competitively inhibited by cyclodextrins may also be purified by cyclodextrin affinity chromatography. Therefore, cyclodextrin affinity chromatography can function in the purification of such amylolytic enzymes with the interaction occurring at a site removed from the active site. In such cases it appears that the cyclodextrin is interacting with an affinity site or binding site that is present on some amylolytic enzymes. It seems that certain similarities occur among the binding sites of such enzymes. Literature concerning amylases, and their subsequent purification using cyclodextrin affinity chromatography is reviewed and the fundamental basis of the interaction of the cyclodextrin with amylolytic enzymes is discussed here.

Affinity capillary electrophoretic studies of complexation between dextrin oligomers and polyiodides

Capillary electrophoresis (CE) has been applied to the study of complexation between dextrins and polyiodides. A baseline separation of fluorescently labeled dextrin oligomers has provided a unique platform for the observation of a contribution of single oligomers to the complexation process that could previously be measured only in bulk. The complex formation was easily recognized through comparison of peak migration times and peak shapes in the presence and absence of polyiodides. The degree of polymerization (DP) number was found crucial in the binding process, but the I2/I- ratio in a solution also appeared to determine the nature of complexation. The effects of buffer pH and ionic strength upon complexation were also briefly investigated. Diodearray spectra in the visible wavelength range confirmed the differential complexation of unlabeled maltodextrins with different DP values after a CE iodine affinity separation. 13C-nuclear magnetic resonance (NMR) spectral data on differently sized dextrin fractions were found to be in good agreement with the results from CE measurements.

Thermodynamics of ligand binding to the starch-binding domain of glucoamylase from Aspergillus niger

The thermodynamics of ligand binding to the starch-binding domain (SBD) of glucoamylase from Aspergillus niger has been studied using titration calorimetry. The ligand binding was studied both with the SBD fragment as well as glucoamylase G1 which contains both a catalytic domain and SBD. The ligands were beta-cyclodextrin and three thiopanose analogues [panose = alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->4)-D-Glcp] each including an alpha-(1-->6) thioglycosidic linkage at the non-reducing end. beta-Cyclodextrin binds more strongly than the thiopanose analogues and these have a slightly increasing binding constant with chain length. The reactions are enthalpy-driven with unfavourable contributions from entropy and the variations in enthalpy and entropy compensate each other linearly. SBD was shown to have two binding sites that appear to bind identically and independently in the isolated binding domain, whereas they interact with each other in a negatively cooperative fashion when the catalytic domain of glucoamylase is present (glucoamylase G1). In glucoamylase G1 one site of SBD has an increased binding constant compared to the SBD fragment, whereas the other has the same association constant. The change in binding constant and induced cooperativity were not due to interactions with the catalytic binding site, since binding of beta-cyclodextrin was the same both when the catalytic site was occupied by the strong inhibitor acarbose and when the catalytic site was free.

Specificity of the binding domain of glucoamylase 1

Glucoamylase 1 from Aspergillus niger hydrolyses granular starch at an increased rate due to the presence of a C-terminal starch-binding domain. This domain was isolated and shown to bind to the malto-oligosaccharides Glc2 to Glc11 with a stoichiometry of 1 mol ligand/mol protein. The affinity for these ligands increased with increasing degree of polymerisation until Glc9, above which no further increase was observed. We suggest that this indicates that for maximum affinity the substrate should be able to form a helical conformation, which mimics the conformation of amylose in granular starch. We propose a model of how the complex between the malto-oligosaccharides and the binding domain is formed and indicate how this affects the differences in binding modes for soluble and insoluble substrates. Glucono-1,5-lactone interacts with the binding domain at a different site to the malto-oligosaccharides allowing the formation of a ternary complex between the binding domain, a malto-oligosaccharide and glucono-1,5-lactone. The binding domain also binds to linear alpha-1,6-linked glucose digosaccharides (dextran), but with much lower affinity than for alpha-1,4-linked glucose. This ligand appears to interact with the binding domain at both binding sites, i.e. at the site to which the malto-oligosaccharides bind and also at the site to which glucono-1,5-lactone binds. The relevance of the results to the mechanism of action of other polysaccharide-hydrolysing enzymes containing both a catalytic and a binding domain is discussed.