Measurement of total starch in cereal products by amyloglucosidase-alpha-amylase method: collaborative study.
McCleary, B. V., Gibson, T. S. & Mugford, D. C. (1997). Journal of AOAC International, 80, 571-579.
An American Association of Cereal Chemists/AOAC collaborative study was conducted to evaluate the accuracy and reliability of an enzyme assay kit procedure for measurement of total starch in a range of cereal grains and products. The flour sample is incubated at 95 degrees C with thermostable alpha-amylase to catalyze the hydrolysis of starch to maltodextrins, the pH of the slurry is adjusted, and the slurry is treated with a highly purified amyloglucosidase to quantitatively hydrolyze the dextrins to glucose. Glucose is measured with glucose oxidase-peroxidase reagent. Thirty-two collaborators were sent 16 homogeneous test samples as 8 blind duplicates. These samples included chicken feed pellets, white bread, green peas, high-amylose maize starch, white wheat flour, wheat starch, oat bran, and spaghetti. All samples were analyzed by the standard procedure as detailed above; 4 samples (high-amylose maize starch and wheat starch) were also analyzed by a method that requires the samples to be cooked first in dimethyl sulfoxide (DMSO). Relative standard deviations for repeatability (RSD(r)) ranged from 2.1 to 3.9%, and relative standard deviations for reproducibility (RSD(R)) ranged from 2.9 to 5.7%. The RSD(R) value for high amylose maize starch analyzed by the standard (non-DMSO) procedure was 5.7%; the value was reduced to 2.9% when the DMSO procedure was used, and the determined starch values increased from 86.9 to 97.2%.
Measurement of carbohydrates in grain, feed and food.
McCleary, B. V., Charnock, S. J., Rossiter, P. C., O’Shea, M. F., Power, A. M. & Lloyd, R. M. (2006). Journal of the Science of Food and Agriculture, 86(11), 1648-1661.
Procedures for the measurement of starch, starch damage (gelatinised starch), resistant starch and the amylose/amylopectin content of starch, β-glucan, fructan, glucomannan and galactosyl-sucrose oligosaccharides (raffinose, stachyose and verbascose) in plant material, animal feeds and foods are described. Most of these methods have been successfully subjected to interlaboratory evaluation. All methods are based on the use of enzymes either purified by conventional chromatography or produced using molecular biology techniques. Such methods allow specific, accurate and reliable quantification of a particular component. Problems in calculating the actual weight of galactosyl-sucrose oligosaccharides in test samples are discussed in detail.
Method for the direct determination of available carbohydrates in low-carbohydrate products using high-performance anion exchange chromatography.
Ellingson, D., Potts, B., Anderson, P., Burkhardt, G., Ellefson, W., Sullivan, D., Jacobs, W. & Ragan, R. (2010). Journal of AOAC International, 93(6), 1897-1904.
An improved method for direct determination of available carbohydrates in low-level products has been developed and validated for a low-carbohydrate soy infant formula. The method involves modification of an existing direct determination method to improve specificity, accuracy, detection levels, and run times through a more extensive enzymatic digestion to capture all available (or potentially available) carbohydrates. The digestion hydrolyzes all common sugars, starch, and starch derivatives down to their monosaccharide components, glucose, fructose, and galactose, which are then quantitated by high-performance anion-exchange chromatography with photodiode array detection. Method validation consisted of specificity testing and 10 days of analyzing various spike levels of mixed sugars, maltodextrin, and corn starch. The overall RSD was 4.0 across all sample types, which contained within-day and day-to-day components of 3.6 and 3.4, respectively. Overall average recovery was 99.4 (n = 10). Average recovery for individual spiked samples ranged from 94.1 to 106 (n = 10). It is expected that the method could be applied to a variety of low-carbohydrate foods and beverages.
β-Galactosidase from Bifidobacterium adolescentis DSM20083 prefers β-(1,4)-galactosides over lactose.
Hinz, S. W. A., Van den Broek, L. A. M., Beldman, G., Vincken, J. P. & Voragen, A. G. J. (2004). Applied Microbiology and Biotechnology, 66(3), 276-284.
A β-galactosidase gene (β-Gal II) from Bifidobacterium adolescentis DSM 20083 was cloned into a pbluescript SK (−) vector and expressed in Escherichia coli. The recombinant enzyme was purified from the cell extract by anion-exchange and size-exclusion chromatography. β-Gal II had a native molecular mass of 235 kDa and the subunits had a molecular mass of 81 kDa, indicating that β-Gal II occurs as a trimer. The enzyme was classified as belonging to glycosyl hydrolase family 42. The optimal pH was 6.0 and the optimal temperature was 50°C, using p-nitrophenyl-β-D-galactopyranoside as a substrate. The K m and V max for Gal(β1–4)Gal were 60 mM and 1,129 U/mg, respectively. The recombinant β-Gal II was highly active towards Gal(β1–4)Gal and Gal(β1–4)Gal-containing oligosaccharides; only low activity was observed towards Gal(β1–3)Gal, lactose, and Gal(β1–3)GalOMe. No activity was found towards Gal(β1–6)Gal, Gal(β1–4)Man, Gal(α1–4)Gal, Gal(α1–3)Gal(β1–4)Gal, cellobiose, maltose and sucrose. β-Gal II was inhibited at high substrate concentrations (100 mg/ml) and no transglycosylation activity was found. At lower substrate concentrations (10 mg/ml) only low transglycosylation activity was found; the Gal/[Gal(β1–4)]2Gal peak area ratio was 9:1.
Kinetic Analyses of Retaining endo-(Xylo) glucanases from Plant and Microbial Sources Using New Chromogenic Xylogluco-Oligosaccharide Aryl Glycosides.
Ibatullin, F. M., Baumann, M. J., Greffe, L. & Brumer, H. (2008). Biochemistry, 47(29), 7762-7769.
A library of phenyl β-glycosides of xylogluco-oligosaccharides was synthesized via a chemoenzymatic approach to produce new, specific substrates for xyloglucanases. Tamarind xyloglucan was completely hydrolyzed to four, variably galactosylated component oligosaccharides based on Glc4 backbones, using a Trichoderma endo-glucanase mixture. Oligosaccharide complexity could be further reduced by β-galactosidase treament. Subsequent per-O-acetylation, α-bromination, phase-transfer glycosylation, and Zemplén deprotection yielded phenyl glycosides of XXXG and XLLG oligosaccharides with a broad range of aglycon pKa values. Kinetic and product analysis of the action of the archetypal plantendo-xyloglucanase, Tropaeolum majus NXG1, on these compounds indicated that formation of the glycosyl−enzyme intermediate was rate-limiting in the case of phenol leaving groups with pKa values of >7, leading exclusively to substrate hydrolysis. Conversely, substrates with aglycon pKa values of 5.4 gave rise to a significant amount of transglycosylation products, indicating a change in the relative rates of formation and breakdown of the glycosyl−enzyme intermediate for these faster substrates. Notably, comparison of the initial rates of XXXG-Ar and XLLG-Ar conversion indicated that catalysis by TmNXG1 was essentially insensitive to the presence of galactose in the negative subsites for all leaving groups. More broadly, analysis of a selection of enzymes from CAZy families GH 5, 12, and 16 indicated that the phenyl glycosides are substrates for anomeric configuration-retaining endo-xyloglucanases but are not substrates for strict xyloglucan endo-transglycosylases (XETs). The relative activities of the GH 5, 12, and 16 endo-xyloglucanases toward GGGG-CNP, XXXG-CNP, and XLLG-CNP reflected those observed using analogous high molar mass polysaccharides. These new chromogenic substrates may thus find wide application in the discovery, screening, and detailed kinetic analysis of new xyloglucan-active enzymes.
An investigation of the substrate specificity of the xyloglucanase Cel74A from Hypocrea jecorina.
Desmet, T., Cantaert, T., Gualfetti, P., Nerinckx, W., Gross, L., Mitchinson, C. & Piens, K. (2007). FEBS Journal, 274(2), 356-363.
The substrate specificity of the xyloglucanase Cel74A from Hypocrea jecorina (Trichoderma reesei) was examined using several polysaccharides and oligosaccharides. Our results revealed that xyloglucan chains are hydrolyzed at substituted Glc residues, in contrast to the action of all known xyloglucan endoglucanases (EC 18.104.22.168). The building block of xyloglucan, XXXG (where X is a substituted Glc residue, and G is an unsubstituted Glc residue), was rapidly degraded to XX and XG (kcat = 7.2 s-1 and Km = 120 µm at 37°C and pH 5), which has only been observed before with the oligoxyloglucan-reducing-end-specific cellobiohydrolase from Geotrichum (EC 22.214.171.124). However, the cellobiohydrolase can only release XG from XXXGXXXG, whereas Cel74A hydrolyzed this substrate at both chain ends, resulting in XGXX. Differences in the length of a specific loop at subsite + 2 are discussed as being the basis for the divergent specificity of these xyloglucanases.
Rheological properties of thermally xyloglucan gel from the seeds of Hymenaea courbaril.
Busato, A. P., Reicher, F., Domingues, R. & Silveira, J. L. M. (2009). Materials Science and Engineering: C, 29(2), 410-414.
A Brazilian source of galactoxyloglucan was obtained from seeds of Hymenaea courbaril and investigated before (JN) and after the hydrolytic removal of galactose (JH). The native polysaccharide contained glucose, xylose and galactose in a ~ 4.0:2.7:1 molar ratio. Gelation occurred when ~ 51% of the galactose residues was removed from the xyloglucan by fungal β-galactosidase. The rheological properties of JN and JH were analyzed. Dynamic oscillatory measurements characterized JN as a viscoelastic solution and JH as a true gel. JH achieved the maximum storage modulus G′ at temperatures above 40°C and was found to increase with the increasing concentration. The gel point temperatures of JH fraction were determined at the cross-over point of G′ and G″ and by calculating the inflexion point of the G′ plot.
A high molecular arabinogalactan from Ribes nigrum L.: influence on cell physiology of human skin fibroblasts and keratinocytes and internalization into cells via endosomal transport.
Zippel, J., Deters, A., Pappai, D. & Hensel, A. (2009). Carbohydrate Research, 344(8), 1001-1008.
An arabinogalactan protein (F2) was isolated in 1.5% yield from the seeds of Ribes nigrum L. (Grossulariaceae) by aqueous extraction and a one-step anion exchange chromatography on DEAE-Sephacel with 24% galactose, 43% arabinose, and 20% xylose as main carbohydrate residues. Methylation analysis revealed the presence of a 1,3-/1,3,6-galactose backbone, side chains from arabinose in different linkages, and terminal xylose residues. The polysaccharide which turned out to be an arabinogalactan protein had a molecular weight of >106 Da and deaggregated under chaotropic conditions. The cellular dehydrogenase activities (MTT and WST-1 tests) of human skin cells (fibroblasts, keratinocytes) as well as the proliferation rate of keratinocytes (BrdU incorporation ELISA) were significantly stimulated by the polymer at 10 and 100 µg/mL. F2 had no influence on differentiation status of keratinocytes and did not exhibit any cytotoxic potential (LDH test). The biological activity of F2 was not dependent on the high molecular weight. Influence of the polysaccharide on the gene expression of specific growth factors, growth factor receptors, signal proteins and marker proteins for skin cell proliferation, and differentiation by RT-PCR could not be shown. Gene array investigations indicated an increased expression of various genes encoding for catabolic enzymes, DNA repair, extracellular matrix proteins, and signal transduction factors. Removal of terminal arabinose residues by α-L-arabinofuranosidase did not influence the activity toward skin cells, while the treatment with β-D-galactosidase yielded an inactive polysaccharide. The FITC-labeled polysaccharide was incorporated in a time-dependent manner into human fibroblasts (laser scanning microscopy) via endosomal transport. This internalization of the polysaccharide was inhibited by Cytochalasin B.
Crystal structures of Clostridium thermocellum xyloglucanase, XGH74A, reveal the structural basis for xyloglucan recognition and degradation.
Martinez-Fleites, C., Guerreiro, C. I. P.D., Baumann, M. J., Taylor, E. J., Prates, J. A. M., Ferreira, L. M. A., Fontes, C. M. G. A., Brumer, H. & Davies, G. J. (2006). Journal of Biological Chemistry, 281(34), 24922-24933.
The enzymatic degradation of the plant cell wall is central both to the natural carbon cycle and, increasingly, to environmentally friendly routes to biomass conversion, including the production of biofuels. The plant cell wall is a complex composite of cellulose microfibrils embedded in diverse polysaccharides collectively termed hemicelluloses. Xyloglucan is one such polysaccharide whose hydrolysis is catalyzed by diverse xyloglucanases. Here we present the structure of the Clostridium thermocellum xyloglucanase Xgh74A in both apo and ligand-complexed forms. The structures, in combination with mutagenesis data on the catalytic residues and the kinetics and specificity of xyloglucan hydrolysis reveal a complex subsite specificity accommodating seventeen monosaccharide moieties of the multibranched substrate in an open substrate binding terrain.
Solubilization of galactosyltransferase that synthesizes 1,4‐β-galactan side chains in pectic rhamnogalacturonan I.
Geshi, N., Pauly, M. & Ulvskov, P. (2002). Physiologia Plantarum, 114(4), 540-548.
β-1,4-Galactan galactosyltransferase (GT) activity was solubilized from potato microsomal membranes in the presence of 78 mM 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonic acid. The solubilized GT activity transferred 14[C]galactose from UDP-14[C]galactose onto the acceptor-substrates composed of rhamnogalacturonan (RG) with short galactan chains (RG-A, approximately 1.2 MDa, mol% Gal/Rha = 0.7; RG-B, approximately 21 kDa, mol% Gal/Rha = 1.2). However, shorter RG containing short galactan chains (approximately 2 kDa and 1.2 kDa), RG oligomers without galactosyl-residues, galactan, and galactooligomers did not act as acceptor-substrates. Optimal pH for 14[C] incorporation onto RG-A and RG-B was around 5.6 and 7.5, respectively. The 14[C]-labelled products synthesized upon RG-A and RG-B could be digested with a RG specific lyase into smaller RG fragments. 1,4-β-Endogalactanase could not digest the former product, whereas the latter product was digested to 14[C] galactobiose- and 14[C]galactose. This demonstrates that at least two GT activities were solubilized from potato microsomal membranes. One had optimal pH around 5.6 to transfer galactosyl residues onto RG-A, whereas the other had optimal pH around 7.5 to transfer galactosyl residues onto RG-B. Both synthesized galactan attached to the RG backbone of RG-A and RG-B, and the galactan synthesized onto the RG-B acceptor was 1,4-β-linked.
Substrate specificities of glycosidases from Aspergillus species pectinase preparations on elderberry anthocyanins.
Pricelius, S., Murkovic, M., Souter, P. & Guebitz, G. M. (2009). Journal of Agricultural and Food Chemistry, 57(3), 1006-1012.
Attractive color is one of the most important sensory characteristics of fruit and berry products, and elderberry juice is widely used as natural colorant. When pectinase preparations were used in the production of elderberry juice for clarification, a concomitant decrease of anthocyanins and thus a color loss were observed. This paper demonstrates that this is due to side glycosidase activities contained in commercial pectinase preparations from Aspergillus sp. Using LC-MS, sequential deglycosylation of cyanidin-3-sambubioside, cy-3-glucoside, cy-3-sambubioside-5-glucoside, and cy-3,5-diglucoside was found to be catalyzed by specific glycosidases contained in the pectinase preparations. There was no big difference in the deglycosylation rate between monoglucosidic or diglucosidic anthocyanins. However, the degradation rate was decreased when rutinose was attached to cyanidin, whereas the structure of the aglycone itself had almost no influence. Pure β-glucosidases from Agrobacterium species and Aspergillus niger and the β-glucosidase N188 from A. niger did not show any conversion of anthocyanins, indicating the presence of specific glycosidases. Thus, an activity gel based assay was developed to detect anthocyanin-specific glycosidase activity in enzyme preparations, and according to LC-MS peptide mass mapping of digested bands, homologies to a β-glucosidase from Aspergillus kawachii were found.