Structure of branching enzyme- and amylomaltase modified starch produced from well-defined amylose to amylopectin substrates

The branching ratio of enzymatically synthesized α-glucans impacts microbiome and metabolic outcomes of in vitro fecal fermentation

The aim of this study was to evaluate the impacts of enzymatically synthesized α-glucans possessing α-1,4- and α-1,6-glucose linkages, and varying in branching ratio, on colonic microbiota composition and metabolic function. Four different α-glucans varying in branching ratio were synthesized by amylosucrase from Neisseria polysaccharea and glycogen branching enzyme from Rhodothermus obamensis. The branching ratios were found to range from 0 % to 2.8 % using GC/MS. In vitro fecal fermentation analyses (n = 8) revealed that the branching ratio dictates the short-chain fatty acid (SCFA) generation by fecal microbiota. Specifically, slightly branched (0.49 %) α-glucan resulted in generation of significantly (P < 0.05) higher amounts of propionate, compared to more-branched counterparts. In addition, the amount of butyrate generated from this α-glucan was statistically (P > 0.05) indistinguishable than those observed in resistant starches. 16S rRNA sequencing revealed that enzymatically synthesized α-glucans stimulated Lachnospiraceae and Ruminococcus related OTUs. Overall, the results demonstrated metabolic function of colonic microbiota can be manipulated by altering the branching ratio of enzymatically synthesized α-glucans, providing insights into specific structure-function relationships between dietary fibers and the colonic microbiome. Furthermore, the slightly branched α-glucans could be used as functional carbohydrates to stimulate the beneficial microbiota and SCFAs in the colon.

Sequential starch modification by branching enzyme and 4-α-glucanotransferase improves retention of curcumin in starch-alginate beads

A new super-branched amylopectin with longer exterior chains was produced from normal maize starch by modification with branching enzyme followed by 4-α-glucanotransferase, and applied for co-entrapment of a curcumin-loaded emulsion in alginate beads. The network structure of the gel beads was obtained with Ca2+-cross-linked alginate and a modest load of retrograded starch. The dual enzyme modified starch contained more and longer α-1,6-linked branch chains than single enzyme modified and unmodified starches and showed superior resistance to digestive enzymes. Alginate beads with or without starch were of similar size (1.69-1.74 mm), but curcumin retention was improved 1.4-2.8-fold in the presence of different starches. Thus, subjecting the curcumin-loaded beads to in vitro simulated gastrointestinal digestion resulted in retention of 70, 43 and 22 % of the curcumin entrapped in the presence of modified, unmodified, or no starch, respectively. Molecular docking provided support for curcumin interacting with starch via hydrogen bonding, hydrophobic contacts and π-π stacking. The study highlights the potential of utilizing low concentration of dual-enzyme modified starch with alginate to create a versatile vehicle for controlled release and targeted delivery of bioactive compounds.

Production of highly branched α-limit dextrins with enhanced slow digestibility by various glycogen-branching enzymes

α-Limit dextrins (α-LDx) are slowly digestible carbohydrates that attenuate postprandial glycemic response and trigger the secretion of satiety-related hormones. In this study, more highly branched α-LDx were enzymatically synthesized to enhance the slowly digestible property by various origins of glycogen branching enzyme (GBE), which catalyzes the transglycosylation to form α-1,6 branching points after cleaving α-1,4 linkages. Results showed that the proportion of branched α-LDx in starch molecules increased around 2.2-8.1 % compared to α-LDx from starch without GBE treatment as the ratio of α-1,6 linkages increased after different types of GBE treatments. Furthermore, the enzymatic increment of branching points enhanced the slowly digestible properties of α-LDx at the mammalian α-glucosidase level by 17.3-28.5 %, although the rates of glucose generation were different depending on the source of GBE treatment. Thus, the highly branched α-LDx with a higher amount of α-1,6 linkages and a higher molecular weight can be applied as a functional ingredient to deliver glucose throughout the entire small intestine without a glycemic spike which has the potential to control metabolic diseases such as obesity and type 2 diabetes.

Deciphering the structural and functional characteristics of an innovative small cluster branched α-glucan produced by sequential enzymatic synthesis

Highly branched α-glucan (HBAG) proved to be a promising material as an osmotic agent in peritoneal dialysis solutions. However, high resistance of HBAG to amylolytic enzymes might be a potential drawback for peritoneal dialysis due to its high degree of branching (20-30 %). To address this issue, we designed a small-clustered α-glucan (SCAG) with a relatively low molecular weight (Mw) and limited branching. Structural characteristics revealed that SCAG was successfully synthesized by modifying waxy rice starch (WRS) using sequential maltogenic α-amylase (MA) and starch branching enzyme (BE). The Mw of SCAG was 1.40 × 10⁵ Da, and its (α1 → 6) bonds ratio was 8.93 %, which was below that of HBAG. A relatively short branch distribution was observed in SCAG (CL = 6.27). Short-range orderliness of WRS was reduced from 0.749 to 0.322 with the MABE incubation. Additionally, SCAG had an extremely low viscosity (~12 cP) and nearly no retrogradation. Although the resistance of SCAG to amylolytic enzymes was enhanced by 15.22 % compared with native WRS, the extent was significantly lower than that of HBAG in previous studies. These new findings demonstrate the potential of SCAG as a novel functional α-glucan in food and pharmaceutical applications.

Effect of Starch Primers on the Fine Structure of Enzymatically Synthesized Glycogen-like Glucan

Glycogen-like glucan (GnG) is a unique hyperbranched polysaccharide nanoparticle which is drawing increasing attention due to its biodegradability and abundant short branches that can be functionalized. Because starch and GnG are both composed of glucose residues and have similar glucosidic bonds, GnG could be fabricated by sucrose phosphorylase, α-glucan phosphorylase, and branching enzymes from starch primers and sucrose. In this study, high-amylose starch, normal starch, and waxy corn starch were used as primers to synthesize GnG, and their impact on the fine structure of GnG was investigated. Structural analysis indicated that with increasing content of amylopectin in the starch primer, the proportion of short chains in GnG decreased, and the degree of β-amylolysis and α-amylolysis was enhanced. Amylose in the primer contributed to a compact and homogeneous structure of GnG, while amylopectin triggered the formation of branch points with a more open distribution. These findings provide a new strategy for regulating the fine structure of GnG.

Differentiated structure of synthetic glycogen-like particle by the combined action of glycogen branching enzymes and amylosucrase

Glycogen-like particles (GLPs) were built up from sucrose by applying de novo one-pot enzymatic process of amylosucrase (ASase; 6 U·mL^-1) and glycogen branching enzymes (GBEs; 0.001 and 0.005 U·mL^-1). Due to different chain-length transferring patterns of GBEs, structurally differentiated GLPs were synthesized. Yields of GLPs synthesized at pH 7.0 and 30 °C were improved by increasing the GBE/ASase ratio. Branching degrees of GLPs obviously was increased along with the ratio of GBEs, of which result was directly supported by shortened branch-chain length with greater GBE activity. Long branch chains seemed to play as efficient acceptor molecules to bind newly transferred branch chains especially at lower ratio of GBE/ASase, resulting in greater molecular weight and size of GLP with higher proportion of them. Molecular weight, size, and density of GLPs were ranged from 7.37 × 10⁵ to 1.94 × 10⁸ g·mol^-1, from 23.70 to 52.65 nm, and from 7.99 to 374.32 g·mol^-1·nm^-3, respectively. By increasing GBE/ASase ratio, more compact GLP architecture was fabricated due to increased weight and reduced size with exception of a unique GBE. GLPs were efficiently synthesized by two different glycosyltransferases, and their chemical structures were controllable by source and ratio of GBEs due to their different branch-chain transferring specificity.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Two 1,4-α-glucan branching enzymes successively rearrange glycosidic bonds: A novel synergistic approach for reducing starch digestibility

Enzymatically rearranging α-1,4 and α-1,6 glycosidic bonds in starch is a green approach to regulating its digestibility. A two-step modification process successively catalyzed by 1,4-α-glucan branching enzymes (GBEs) from Rhodothermus obamensi STB05 (Ro-GBE) and Geobacillus thermoglucosidans STB02 (Gt-GBE) was investigated as a strategy to reduce the digestibility of corn starch. This dual GBE modification process caused a reduction of 25.8 % in rapidly digestible starch fraction in corn starch, which were more effective than single GBE-catalyzed modification with the same duration. Structural analysis indicated that the dual GBE modified product contained higher branching density, more abundant short branches, and shorter external chains than those in single GBE-modified product. These results demonstrated that a moderate Ro-GBE treatment prior to starch gelatinization caused several suitable alterations in starch molecules, which promoted the transglycosylation efficiency of the following Gt-GBE treatment. This dual GBE-catalyzed modification process offered an efficient strategy for regulating starch digestibility.

Structure and chain conformation characterization of arabinoglucan from by-product of peanut oil processing

A neutral polysaccharide (NPP) from peanut sediment of aqueous extraction process was purified via anion-exchange and gel-filtration chromatography. The weight-average molecular weight and polydispersity index were 3.36 × 10⁴ Da and 1.06. Composition of glucose (82.66 %, molar percentage) and arabinose (17.34 %) suggested an arabinoglucan structure. Multiple medium-length chains consisting of many 1,4-linked α-Glcp and a few 1,5-linked α-Araf maintained the main chain structure. The backbone was substituted at O-6 and O-3 positions, attached by side chains consisting of two to six α-Glcp and terminated with Araf and Glcp. Degree of branching was 42.50 %. Aggregates formed in NPP aqueous solution. They were eliminated by DMSO combining with sonication. Consequently, the average radius of gyration (R_g), hydrodynamic radius (R_h), and R_g/R_h ratio were 17.0 nm, 5.8 nm and 2.93, respectively, indicating extended rigid chain conformation. The backbone substituted at O-3 and short branching chains probably together induced this conformation.

Amylomaltase from Thermus filiformis: expression in Saccharomyces cerevisiae and its use in starch modification

AIM

To express amylomaltase from Thermus filiformis (TfAM) in a generally recognized as safe (GRAS) organism and to use the enzyme in starch modification.

METHODS AND RESULTS

TfAM was expressed in Saccharomyces cerevisiae, using 2% (w/v) galactose inducer under GAL1 promoter. The enzyme was thermostable with high disproportionation and cyclization activities. The main large-ring cyclodextrin (CD) products were CD24-CD29, with CD26 as maximum at all incubation times. TfAM was used to modify cassava and pea starches, the amylose content decreased 18% and 30%, respectively, when 5% (w/v) starch was treated with 0·5 U TfAM g-1 starch. The increase in short branched chain (DP, degree of polymerization, 1-5) and the broader chain length distribution pattern which extended to the longer chain (DP40) after TfAM treatment were observed. The thermal property was changed, with an increase in retrogradation of starch as suggested by a lower enthalpy.

CONCLUSIONS

TfAM was successfully expressed in S. cerevisiae and was used to make starches with new functionality.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report on the expression of AM in the GRAS yeast and the production of a modified starch gel from pea starch to improve the versatility of starch for food use.

Thermophilic 4-α-Glucanotransferase from Thermoproteus Uzoniensis Retards the Long-Term Retrogradation but Maintains the Short-Term Gelation Strength of Tapioca Starch

Gelation of starch is a process during short-term retrogradation. However, long-term retrogradation always leads to the quality deterioration of starch-based food. In this work, a new type of modified tapioca starch (MTS) gel with maintained short-term gelation strength and retarded long-term retrogradation was prepared using a novel recombinantly produced and characterized 4-α-glucanotransferase (TuαGT). In the resulting MTS, the exterior chains of the amylopectin part were elongated and the content of amylose was reduced because of the disproportionation activity of TuαGT. The retrogradation analysis demonstrated that the MTS possessed highly weakened long-term retrogradation characteristics as compared to the native starch. Most importantly, the strength of the gel formed by regelatinized MTS is very close to that of gelatinized native tapioca starch when storing below 30 °C. These findings provide a starting point for developing a novel method for the enzymatic modification of the starch-based gels.