High-performance anion-exchange chromatography with pulsed amperometric detection of linear and branched glucose oligosaccharides

"Non-Naked" Gold with Glucose Oxidase-Like Activity: A Nanozyme for Tandem Catalysis

It has been widely reported that "naked" gold nanoparticles (Au NPs) without protectors have glucose oxidase (GOx)-like activity, and the use of protectors can inhibit the GOx-like activity. Here, "non-naked" Au NPs with GOx-like activity are synthesized by using protein as protector. Although "naked" Au NPs have peroxidase-like activity and GOx-like activity, the optimal pH ranges of the both activities are obviously different. Fortunately, as-synthesized "non-naked" Au NPs show the dual enzyme-like activities at the same pH. So, "non-naked" Au NPs can be described as "tandem nanozyme." As another bonus, the participation of protein protector can stabilize the GOx-like activity and make Au NPs modifiable. Even though Au NPs are connected with graphene oxide (GO), the GOx-like activity is still not changed. Further, Au NPs-GO nanocomposites are applied on the one-pot nonenzymatic glucose colorimetric detection. The "non-naked" gold not only broadens the species of tandem nanozymes, but also facilitates the functionalization of nanozymes, which is promising for immunoassay, biosensor, and medical treatment.

Quantification of sugars in wheat flours with an HPAEC-PAD method

An HPAEC-PAD method has been developed and validated for the simultaneous determination and quantification of six sugars (glucose, isomaltose, maltose, maltotriose, maltotetraose and maltopentaose) in wheat flours, by extraction with water and precipitation of proteins with Carrez II. Analyses were carried out on a Hamilton RCX-30 column with a gradient elution of NaOH 50mM (A) and NaOH 50mM+NaAcO 500 mM (B). Total run time was 38 min. Detector conditions were as follows: E1, +100 mV; E2, +550 mV; E3, -100 mV. The method was validated, with LODs ranging between 0.03-0.21 mg L(-1) and LOQs between 0.10-0.71 mg L(-1), R(2) between 0.9941 and 0.9983; recoveries were from 74.16% to 110.86% and RSDs for intraday repeatability, interday repeatability and reproducibility between 0.35-8.34%, 2.34-6.64% and 1.90-5.68%, respectively. The method was successfully applied to quantification of these sugars in wheat flours.

Phloem sap collection from lettuce (Lactuca sativa L.): Chemical comparison among collection methods

The chemical composition of phloem sap from lettuce, collected by three different methods, was compared. Phloem sap from stylectomy samples contained sucrose and 14 amino acids. Honeydew and EDTA chelation samples showed considerable breakdown of sucrose into fructose and glucose, several additional amino acids, and large differences in relative concentrations of amino acids, when compared to stylectomy samples. Honeydew contained considerable amounts of other oligosaccharides, and few proteins in low amounts, while EDTA showed many proteins. HPLC chromatograms showed numerous unidentified secondary plant compounds in honeydew and EDTA samples. Comparison of phloem sap samples from near-isogenic susceptible and resistant lines showed no relation of phloem sap composition with monogenic resistance to the aphidNasonovia ribisnigri.

Development of an ion-exchange chromatography method for monitoring the degradation of prebiotic arabinoxylan-oligosaccharides in a complex fermentation medium

Arabinoxylan-oligosaccharides (AXOS) are a new class of prebiotics with promising health-promoting characteristics. However, the mechanism by which bacteria break down these compounds in the colon is still uncharacterized, due to their structural complexity. A new analytical method that offers structural information was developed to characterize AXOS degradation during fermentation. The method was based on the simultaneous determination of arabinose, xylose, xylo-oligosaccharides (XOS), and AXOS by applying high-performance anion-exchange chromatography with pulsed amperometric detection. To study the structural features of AXOS in solution without the use of spectroscopic techniques or standards, enzymatic-based reference degradation chromatograms were generated based on enzymes with known specificity. The new method for fingerprinting showed to be a powerful and fast tool to study AXOS degradation with high repeatability with respect to peak area, peak width at half height, and retention time (respective relative standard deviations of ≤3.1%, 2.8%, and 0.8%). This method was successfully applied to study the degradation kinetics of AXOS in a complex fermentation medium by Bifidobacterium longum LMG 11047. The results showed that this strain could use both the arabinose side chains and xylose backbones up to xylotetraose. The characterization of the degradation abilities of AXOS by colon bacteria will allow a better understanding of the beneficial effects of these prebiotics. Furthermore, if the appropriate enzymes are available to design the reference degradation chromatograms, this new method for the qualitative fingerprinting of AXOS breakdown can also be applied for the breakdown of other complex oligosaccharides and polysaccharides.

Will isomalto-oligosaccharides, a well-established functional food in Asia, break through the European and American market? The status of knowledge on these prebiotics

This critical review article presents the current state of knowledge on isomalto-oligosaccharides, some well known functional oligosaccharides in Asia, to evaluate their potential as emergent prebiotics in the American and European functional food market. It includes first a unique inventory of the different families of compounds which have been considered as IMOs and their specific structure. A description has been given of the different production methods including the involved enzymes and their specific activities, the substrates, and the types of IMOs produced. Considering the structural complexity of IMO products, specific characterization methods are described, as well as purification methods which enable the body to get rid of digestible oligosaccharides. Finally, an extensive review of their techno-functional and nutritional properties enables placing IMOs inside the growing prebiotic market. This review is of particular interest considering that IMO commercialization in America and Europe is a topical subject due to the recent submission by Bioneutra Inc. (Canada) of a novel food file to the UK Food Standards Agency, as well as several patents for IMO production.

Study of molar response of dextrans in electrochemical detection

In this work, a methodological approach is reported, aimed at assessing the electrochemical response of some model gluco-oligosaccharides (dextrans). Such strategy is based on the complementary use of both anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and capillary zone electrophoresis coupled with UV detection (CZE-UV). Unlike HPAEC-PAD, CZE-UV required derivatization with a chromophoric dye (i.e., 8-aminonaphtalene-1,3,6-trisulphonic acid, ANTS) to enhance UV response and separation selectivity. From the comparison between chromophore response and PAD signal, the reliability of HPAEC-PAD for quantitative evaluation of dextran mixtures containing mainly oligomers with polymerization degree (DP) up to 18 could be proved, due to the fairly constant molar response. For higher DPs (up to 41), a maximum in the trend of the molar responses was observed followed by a steep decrease for DPs higher than about 30-35; indeed, an underestimation of weight-average molecular weight of dextran mixtures containing such oligomers was noticed.

Determination of average degree of polymerisation and distribution of oligosaccharides in a partially acid-hydrolysed homopolysaccharide: A comparison of four experimental methods applied to mannuronan

The average degree of polymerisation (DP) and distribution of oligosaccharides in partially acid hydrolysed mannuronans were quantitatively evaluated by 1H NMR, electrospray ionisation mass spectrometry (ESI-MS), micellar electrokinetic capillary chromatography with UV detection (MEKC-UV), and high-pressure anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Our investigation shows that 1H NMR, MEKC-UV and, in particular, HPAEC-PAD can be used as quantitative tools to aid the investigation of polysaccharide structure, function and synthesis. For the latter two techniques, especially, this represents a significant new development as it enables calculation of the quantity of individual oligomers of nominal DP by direct analysis of a defined oligomer mixture. Appropriate statistical averages of number and weight distributions were also calculated and found to fit very well to predicted Kuhn distributions that assume random depolymerisation.

High-performance anion-exchange chromatography-electrospray mass spectrometry for investigation of the substituent distribution in hydroxypropylated potato amylopectin starch

The use of high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) coupled on-line with electrospray mass spectrometry (ESI-MS) for analysis of the substitution pattern in chemically modified starch, has been investigated. In order to characterise the distribution of substitution groups along the polymer chain, hydroxypropylated potato amylopectin starch (HPPAP) was subjected to enzymic hydrolysis, followed by analysis of the degradation products by HPAEC-PAD-MS. When using conventional chromatographic techniques for characterisation of enzymic hydrolysates, standard compounds are required for identification of the hydrolysis products. However, the on-line coupling with ESI-MS allowed identification of all products obtained, substituted as well as unsubstituted, and also of those compounds that co-eluted, without the need for standards. Further, HPAEC-PAD-MS was shown to be useful for analysis of the substitution pattern in modified starch; from results obtained it was suggested that the hydroxypropyl groups were homogeneously distributed in the amylopectin molecule. It was also shown that the starch hydrolysing enzymes were hindered by the hydroxypropyl groups and preferentially cleaved glucosidic linkages between unsubstituted glucose units.

Purification and characterisation of a malto-oligosaccharide-forming amylase active at high pH from Bacillus clausii BT-21

Bacillus clausii BT-21 produced an extracellular malto-oligosaccharide-forming amylase active at high pH when grown on starch substrates. The enzyme was purified to homogeneity by affinity and anion-exchange chromatography. The molecular weight of the enzyme estimated by sodium dodecyl sulfate polyacrylamide electrophoresis was 101 kDa. The enzyme showed an optimum of activity at pH 9.5 and 55 degrees C. Maltohexaose was detected as the main initially formed starch hydrolysis product. Maltotetraose and maltose were the main products obtained after hydrolysis of starch by the enzyme for an extended period of time and were not further degraded. The enzyme readily hydrolysed soluble starch, amylopectin and amylose, while cyclodextrins, pullulan or dextran were not degraded. The mode of action during hydrolysis of starch indicated an exo-acting type of amylolytic enzyme mainly producing maltohexaose and maltotetraose. Amino acid sequencing of the enzyme revealed high homology with the maltohexaose-forming amylase from Bacillus sp. H-167.

Functional food properties of non-digestible oligosaccharides: a consensus report from the ENDO project (DGXII AIRII-CT94-1095)

This paper results from the final phase of the ENDO project (DGXII AIRII-CT94-1095), a European Commission-funded project on non-digestible oligosaccharides (NDO). All participants in the programme met to perform a consensus exercise on the possible functional food properties of NDO. Topics studied during the project (including a workshop on probiotics and prebiotics) and related aspects, for which considerable evidence has been generated recently, were evaluated on the basis of existing published scientific evidence. There was a general consensus that: (1) there is strong evidence for a prebiotic effect of NDO in human subjects. A prebiotic effect was defined as a food-induced increase in numbers and/or activity predominantly of bifidobacteria and lactic acid bacteria in the human large intestine; (2) there is strong evidence for the impact that NDO have on bowel habit; (3) there is promising evidence that consumption of inulin-type fructans may result in increased Ca absorption in man; (4) there are preliminary indications that inulin-type fructans interact with the functioning of lipid metabolism; (5) there is preliminary evidence in experimental animals of a preventive effect against colon cancer. Human nutrition studies are needed to substantiate these findings. It was concluded that the nutritional properties of NDO may prove to be a key issue in nutritional research in the future.

Action patterns and mapping of the substrate-binding regions of endo-(1-->5)-alpha-L-arabinanases from Aspergillus niger and Aspergillus aculeatus

The substrate binding sites of endo-(1-->5)-alpha-L-arabinanases (EC 3.2.1.99) from Aspergillus niger and Aspergillus aculeatus were investigated using reduced and regular (1-->5)-alpha-L-arabino-oligosaccharides and high performance anion exchange chromatographic analysis. Calculation of bond cleavage frequencies and kcat/K(m) parameters for these substrates enabled the determination of the number of arabinofuranosyl binding subsites and the estimation of the binding affinities of each subsite. The A. aculeatus endo-arabinanase has six subsites arranged symmetrically around the catalytic site, while the A. niger endo-arabinanase has five subsites; two from the catalytic site towards the non-reducing end of the bound substrate and three toward the reducing end. The two subsites directly adjacent to the catalytic sites in both the A. niger and A. aculeatus endo-arabinanase have near-zero net free energy of binding. These results are unlike most glycopyranosyl endo-hydrolases studied which have net negative (unfavourable) energies of interaction at these two subsites, and may be related to the greater conformational flexibility of arabinofuranosyl residues than glycopyranosyl residues. The complete subsite maps are also rationalized with regard to the observed action patterns of these enzymes on linear (1-->5)-alpha-L-arabinan.

Resolution of the branched forms of oligosaccharides by high-performance capillary electrophoresis

The heterogeneous nature of most polysaccharides found in nature includes distribution in molecular weight, primary sequence, and branching. The analytical methodology used in the characterization of these structural aspects must ensure high separation efficiency and selectivity. This paper reports on the high-performance capillary electrophoresis (HPCE) separation of branched forms of oligosaccharides as well as some variants in the primary structure. Oligosaccharide maps were obtained after selective debranching using isoamylase, laminarinase, and cellulase enzymes. The samples investigated were alpha-D-glucans (amylose, amylopectin, and pullulan) and beta-D-glucans (exemplified by lichenan). The solutes were separated as fluorescent derivatives with 8-aminonaphthalene-1,3,6-trisulfonate (ANTS) and detected by laser-induced fluorescence at 514 nm using a He/Cd laser (excitation at 325 nm). The number of theoretical plates was in excess of one million per meter. Baseline resolution of oligosaccharides with a degree of polymerization approximately 70 was obtained within 15 min using borate buffer as the electrolyte.

Isolation and characterization of rhamnogalacturonan oligomers, liberated during degradation of pectic hairy regions by rhamnogalacturonase

Digests of modified hairy regions of apple pectin (MHR) obtained after degradation by rhamnogalacturonase (RGase) were analyzed for oligomer composition using high-performance anion-exchange chromatography and pulsed amperometric detection. A series of oligomers which appear to be characteristic of RGase degradation could be recognized. These oligomers were isolated on a preparative scale by size-exclusion chromatography and preparative anion-exchange chromatography and analyzed for sugar composition. 1H NMR spectroscopy showed that the oligomers consisted of between 4 and 9 sugar units with a backbone of alternating rhamnose and galacturonic acid residues, partly substituted with galactose residues linked to C-4 of the rhamnose moiety. The HPLC elution pattern showed that higher oligomers were also formed during incubation with RGase. These have the same basic structure but may contain other sugar units in addition to those given above. The oligomer composition of RGase digests of MHR isolated from apple, pear, leek, onion, carrot, and potato was very similar. Using anion-exchange chromatography to monitor the degradation of MHR at increasing incubation times, it was found that all the oligomers were present from the initial stages of the enzyme reaction and that the ratio between the different oligomers remained constant with time. Implications of these results for the structure of MHR and the mechanism of RGase action are discussed.

Determination of the pattern of methyl esterification in pectin. Distribution of contiguous nonesterified residues

A method is described for determining the distribution of contiguous nonesterified galacturonic acid residues within pectins. First, the esterified galacturonic acids are converted to galactose by reduction with sodium borohydride, then the glycosidic linkages of the resulting galactose residues are cleaved selectively by liquid HF solvolysis. Separation and quantitation of the resulting galacturonic acid containing oligomers reveals the proportion of each stretch of contiguous nonesterified galacturonic acid residues in the original pectin. The distribution of nonesterified GalA in a pectin fraction obtained from cotton suspension culture cell walls with approximately 50% esterification appears to be far from random.

Capillary zone electrophoresis of malto-oligosaccharides derivatized with 8-aminonaphthalene-1,3,6-trisulfonic acid

Malto-oligosaccharides were derivatized via their reducing end with 8-aminonaphthalene-1,3,6-trisulfonic acid by reductive amination, and the separation and electrophoretic migration behavior of the labelled sugars were investigated by capillary zone electrophoresis. Series of linear malto-oligosaccharides were found particularly suitable for both the study of the effect of the operating conditions on the separation and the investigation of the relationship between the electrophoretic mobility and the molecular size of the homologues. The electrophoretic mobility of the malto-oligosaccharide conjugates was found to be a linear function of the molecular mass to the negative two-thirds power. The sugar derivatives employed here carry three negative charges due to the presence of the dissociated sulfonic acid groups even at strongly acidic pH. Therefore, the analytes can migrate in the electric field without interference by electroendosmotic flow and/or wall adsorption in uncoated silica capillaries at low pH. As a result, the separation of these carbohydrate conjugates can be carried out under such conditions with high speed and efficiency in free solution, i.e., without an anticonvective medium such as a gel or a viscous polymer solution. Appropriate use of triethylammonium phosphate buffer, pH 2.5, as the background electrolyte improves not only the reproducibility, but also the efficiency and speed of the separation. The labelled sugars allow monitoring of the separation by UV detector or laser-induced fluorescence detector with concomitant enhancement of analytical sensitivity.