Development of an efficient bioprocess for turanose production by sucrose isomerisation reaction of amylosucrase

Characterization of a unique pH-dependent amylosucrase from Deinococcus cellulosilyticus

The amylosucrase (ASase, EC 2.4.1.4) utilizes sucrose as the sole substrate to catalyze multifunctional reactions. It can naturally synthesize α-1,4-linked glucans such as amylose as well as sucrose isomers with more favorable properties than sucrose with a lower intestinal digestibility and non-cariogenic properties. The amino acid sequence of the asase gene from Deinococcus cellulosilyticus (DceAS) exhibits low homology with those of other ASases from other Deinococcus species. In this study, we cloned and expressed DceAS and demonstrated its high activity at pH 6 and pH 8 and maintained stability. It showed higher polymerization activity at pH 6 than at pH 8, but similar isomerization activity and produced more turanose and trehalulose at pH 6 than at pH 8 and produced more isomaltulose at pH 8. Furthermore, the molecular weight of DceAS was 226.6 kDa at pH 6 and 145.5 kDa at pH 8, indicating that it existed as a trimer and dimer, respectively under those conditions. Additionally, circular dichroism spectra showed that the DceAS secondary structure was different at pH 6 and pH 8. These differences in reaction products at different pHs can be harnessed to naturally produce sucrose alternatives that are more beneficial to human health.

Characterization and applications of biomacromolecule structurally similar to glycogen as a dispersion aid and skin protection agent

Glycogen is a naturally occurring or metabolically synthesized biological macromolecule found in a wide range of living organisms, including animals, microorganisms, and even plants. However, naturally sourced glycogen poses challenges for industrial use. This study focused on a biological macromolecule referred to as glycogen-like particles (GLPs), detailing the production methods and biological properties of these particles. In vitro enzymatic production of GLPs was successfully achieved. GLPs synthesized through a simultaneous enzymatic reaction using sucrose had significant changes in their structure and functionality based on the branching enzyme (BE) to amylosucrase (ASase) ratio. As this ratio increased, the GLPs developed higher molecular weights and greater density, solubility, and branching degree while reducing size and turbidity. Structural changes in these enzymes were not observed beyond a critical BE/ASase ratio. Uniformly dispersed curcumin powder was generated in 50 % (w/v) aqueous GLP solution, and the GLPs were non-toxic to human skin keratinocytes at a concentration of 2.5 mg/mL. GLPs with lower branching inhibited tyrosinase activity and melanin synthesis, while those with more long chains displayed effective UV-blocking. By manipulating the BE/ASase ratio, GLPs were shown to display diverse chemical structures and physical characteristics, suggesting their potential application in the food and cosmetics industries.

Secretory expression of amylosucrase in Bacillus licheniformis through twin-arginine translocation pathway

Amylosucrase (EC 2.4.1.4) is a versatile enzyme with significant potential in biotechnology and food production. To facilitate its efficient preparation, a novel expression strategy was implemented in Bacillus licheniformis for the secretory expression of Neisseria polysaccharea amylosucrase (NpAS). The host strain B. licheniformis CBBD302 underwent genetic modification through the deletion of sacB, a gene responsible for encoding levansucrase that synthesizes extracellular levan from sucrose, resulting in a levan-deficient strain, B. licheniformis CBBD302B. Neisseria polysaccharea amylosucrase was successfully expressed in B. licheniformis CBBD302B using the highly efficient Sec-type signal peptide SamyL, but its extracellular translocation was unsuccessful. Consequently, the expression of NpAS via the twin-arginine translocation (TAT) pathway was investigated using the signal peptide SglmU. The study revealed that NpAS could be effectively translocated extracellularly through the TAT pathway, with the signal peptide SglmU facilitating the process. Remarkably, 62.81% of the total expressed activity was detected in the medium. This study marks the first successful secretory expression of NpAS in Bacillus species host cells, establishing a foundation for its future efficient production.

ONE-SENTENCE SUMMARY

Amylosucrase was secreted in Bacillus licheniformis via the twin-arginine translocation pathway.

A unique biochemical reaction pathway towards trehalulose synthesis by an amylosucrase isolated from Deinococcus deserti

The aim of this study was to establish an efficient bioprocess for the synthesis of trehalulose as a novel sweetener. This disaccharide has 70% of the sweetness of sucrose and bioactive properties such as anti-cariogenicity and anti-oxidizing activity. In this study, amylosucrase from the Deinococcus deserti (DdAS) gene was expressed and purified. When DdAS was reacted with 2M sucrose at 35 °C for 120h, the yield ratio of trehalulose to turanose was approximately 2:1. The trehalulose yield increased when extrinsic fructose was added. Under optimum conditions for trehalulose synthesis, the yield reached 36% (246g/L, sucrose basis) starting with 2M sucrose + 0.75M fructose and showed the highest trehalulose productivity (1.94g/L/h). As a result, a novel amylosucrase that synthesized trehalulose as the major product was developed, in contrast to other studied amylosucrase-type enzymes. DdAS could be utilized industrially in a bioprocess for producing trehalulose as a functional sucrose alternative.

Site-Directed Mutagenic Engineering of a Bifidobacterium Amylosucrase toward Greater Efficiency of Turanose Synthesis

The aim of this study was to establish one of the most efficient biocatalytic processes for turanose production by applying a robust Bifidobacterium thermophilum (BtAS) mutant developed through site-directed mutagenesis. A gene encoding the amylosucrase of B. thermophilum (BtAS) was cloned and used as a mutagenesis template. Among the BtAS variants generated by the site-directed point mutation, four different single-point mutants (P200R, V202I, Y265F, and Y414F) were selected to create double-point mutants, among which BtAS_Y414F/P200R displayed the greatest turanose productivity without losing the thermostability of native BtAS. The turanose yield of BtAS_Y414F/P200R reached 89.3% at 50 °C after 6 h with 1.0 M sucrose + 1.0 M fructose. BtAS_Y414F/P200R produced significantly more turanose than BtAS-wild type (WT) by 2 times and completed the reaction faster by another 2 times. Thus, turanose productivity (82.0 g/(L h)) by BtAS_Y414F/P200R was highly improved from 28.1 g/(L h) of BtAS-WT with 2.0 M sucrose + 0.75 M fructose.

Cryoprotective effect of turanose on lyophilized Lactobacillus paracasei subsp. paracasei, L. casei 431

The lyophilization process is the most convenient and successful method to preserve probiotics, although microorganisms are exposed to conditions of extremely low freezing temperatures as well as dehydration. In this study, we evaluated the cryoprotective effect of turanose on Lactobacillus paracasei subsp. paracasei, L. casei 431 (L. casei 431) as a method to increase survival rate by improving cell viability. The results indicated that the viability of L. casei 431 was 9.6% without the cryoprotective agent, whereas bacterial cell viability was increased to 67.1% with the addition of 12% turanose. When turanose-treated freeze-dried cells were stored at 4 °C for 30 days, the survival rate decreased from 67.1 to 53.4%. Furthermore, cell viability significantly decreased by 50% after 30 days when stored at 25 °C with the same amount of turanose. Overall, turanose may be used as an effective cryoprotectant to preserve probiotics against the freeze-drying process and for extended storage at 4 °C.

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.

Physicochemical properties of turanose and its potential applications as a sucrose substitute

Among the structural isomers of sucrose, turanose has been considered as one of good candidates as novel sweetener due to its mild taste, low calorie, and anti-cariogenicity. Here, various physicochemical properties of turanose, such as solubility, temperature and pH stabilities, viscosity, non-enzymatic browning reaction, and dynamic vapor sorption, were investigated by comparing them to those of other commercial sugars. Turanose did not significantly hydrolyze through the simulated digestion tract overall but in the artificial small intestinal environment specifically, turanose degraded by only 18% when sucrose was hydrolyzed by 36% after 4 h. In addition, physicochemical properties of turanose confirmed that it had a potential to replace sucrose due to similar or better product qualities as a food ingredient than other types of sugars with similar chemical structure. Thus, our study suggests that turanose can be applied as a functional sweetener or bulking agent in food processing.

Profiling of Primary Metabolites and Volatile Determinants in Mahlab Cherry (Prunus mahaleb L.) Seeds in the Context of Its Different Varieties and Roasting as Analyzed Using Chemometric Tools

Mahlab cherry (Prunus mahaleb L.) is a plant native to the Mediterranean basin and Eastern Europe, with several health benefits and culinary uses. We explored the compositional heterogeneity in the aroma profile and nutrients of three P. mahaleb seeds in the context of its cultivar type, i.e., white and red, and in response to roasting. A holistic untargeted metabolomics approach was employed for the first time using solid-phase microextraction (SPME-GC-MS) profiles of seed volatiles and primary metabolites coupled with chemometrics. Around 65 peaks belonging to sugars, fatty acids, esters and organic acids were identified by GC-MS. White mahlab from Egypt is rich in fatty acids, e.g., oleic and α-linolenic acids. Some acyl esters, e.g., glycerylmonostearate and n-butylcaprylate, characterized mahlab cultivars from various origins. A total of 135 volatiles were identified, with organic acids and aldehydes the most abundant. Aldehydes were the most discriminatory in seed origin and in accounting for its distinct aroma. Several roasting indices were identified, viz. 1-octanol, γ-caprolactone and isomintlactone. A direct relationship between furans and fatty acids was rationalized by cyclic transformation of the latter into furan derivatives. This study provides the first chemical evidence supporting the nutritional and flavor determinants of mahlab seeds, suggesting novel uses as a functional food.

Chemical Characteristics of Three Kinds of Japanese Soy Sauce Based on Electronic Senses and GC-MS Analyses

Japanese soy sauce has become more acceptable by Chinese consumers due to its umami taste. However, the volatile flavor compounds and taste characters have not been fully clarified. This study aimed to explore the flavor characteristics of three kinds of Japanese soy sauce, including Koikuchi Shoyu, Usukuchi Shoyu, and Amakuchi Shoyu. The secret of volatile flavor substances was investigated by Gas Chromatography-Mass Spectrometry (GC-MS) and electronic nose, while taste compounds were investigated by silylation GC-MS and electronic tongue (E-tongue). A total of 173 volatile flavor substances and 160 taste compounds were identified. In addition, 28 aroma compounds with odor activity values (OAV) ≥ 1 were considered as the typical flavors. We found that alcohols and aldehydes were in high abundance in Japanese soy sauce, but only a small portion of pyrazines and esters were. Based on electronic nose and GC-MS analysis, Koikuchi Shoyu gives more contribution to aroma compounds, while Usukuchi Shoyu and Amakuchi Shoyu give the sourness and sweetness features based on E-tongue and silylation GC-MS analysis. In this study, 50 kinds of sugars were detected that contributed to the sweetness of soy sauce. This study will provide new insight into the flavor characteristics of Japanese soy sauce that potentially contribute to the innovation and development of soy sauce.

Amylosucrase from Deinococcus geothermalis can be modulated under different reaction conditions to produce novel quercetin 4'-O-α-d-isomaltoside

Amylosucrase (ASase, EC.4.2.1.4) is well-known for its distinguishable property of transglycosylation of many flavonoids and phenolics. Quercetin has diverse biological functions, however, its use is limited due to poor solubility and bioavailability. ASase derived from Deinococcus geothermalis (DGAS) showed conditional preference for producing unusual quercetin glucosides (QGs). DGAS produced a variety of QGs including quercetin monoglucosides (QG1), diglucosides (QG2 and QG2'), and triglucoside from quercetin and sucrose. The newly synthesized QG2' was recognized as a novel quercetin isomaltoside with an α-1,6 linkage branched at the -OH of C4' in quercetin by mass and nuclear magnetic resonance spectra. With a higher conversion yield from quercetin to QGs (60-92%), the optimum conditions for producing QG2' were examined under various pH and sucrose concentrations by response surface methodology. QG2' was predominantly produced under acidic conditions (pH 5.0) and at high sucrose concentrations (1000-1500 mM). In contrast, QG1 was generated as an intermediate of consecutive glycosylation. Kinetic evaluations indicated that considerable differences of transglycosylation velocities were caused by the pH and buffer salts of the reaction, which had a 3.9-fold higher overall performance (k_cat/K'_m) of generating QG2' at pH 5 compared to at pH 7. A rationale of unusual transglycosylations was demonstrated with a molecular docking simulation. Taken together, our study demonstrated that ASase can be used to synthesize unusually branched flavonoid glycosides from flavonol aglycones with clear patterns by modulating reaction conditions.

Alkoxycarbonyl elimination of 3-O-substituted glucose and fructose by heat treatment under neutral pH

3-O-Substituted reducing aldoses are commonly unstable under heat treatment at neutral and alkaline pH. In this study, to evaluate the decomposition products, nigerose (3-O-α-d-glucopyranosyl-d-glucose) and 3-O-methyl glucose were heated at 90 °C in 100 mM sodium phosphate buffer (pH 7.5). Decomposition via β-elimination was observed that formed a mixture of 3-deoxy-arabino-hexonic acid and 3-deoxy-ribo-hexonic acid; upon further acid treatment, it was converted to their γ-lactones. Similarly, turanose (3-O-α-d-glucopyranosyl-d-fructose), a ketose isomer of nigerose, decomposed more rapidly than nigerose under the same conditions, forming the same products. These findings indicate that 3-O-substituted reducing glucose and fructose decompose via the same 1,2-enediol intermediate. The alkoxycarbonyl elimination of 3-O-substituted reducing glucose and fructose occurs readily if an O-glycosidic bond is located on the carbon adjacent to the 1,2-enediol intermediate. Following these experiments, we proposed a kinetic model for the3- decomposition of nigerose and turanose by heat treatment under neutral pH conditions. The proposed model showed a good fit with the experimental data collected in this study. The rate constant of the decomposition for nigerose was (1.2 ± 0.1) × 10^-4 s^-1, whereas that for turanose [(2.6 ± 0.2) × 10^-4 s^-1] was about 2.2 times higher.

Amylopectin-Sodium Palmitate Complexes as Sustainable Nanohydrogels with Tunable Size and Fractal Dimensions

Starch-based nanohydrogels with polyelectrolyte characteristics may find unique applications. Herein, the branch chains of amylopectin (AP) were elongated to different extents by amylosucrase, followed by complexation with sodium palmitate (SP) to produce nanohydrogels. Modified AP (mAP) with a longer chain length displayed a better ability to complex with SP, and the mixtures exhibited nanosized particles with an average diameter ranging from 153.5 to 1049.8 nm. The gel strength of bulk nanohydrogels was dependent on the chain length of mAP and SP content, and their fractal dimension was between 1.82 and 2.45. The crystalline structure of native AP was altered from A- to B-type after chain elongation and, subsequently, to B + V-type after complexing with SP. Diffraction peaks of the complexes at 2θ of 7.5°, 12.9°, and 19.8° implied that the AP side chains formed left-handed single helices and the hydrophobic SP was entrapped in the helix cavity.

Comparative study on four amylosucrases from Bifidobacterium species

Amylosucrase (ASase) is α-glucan-producing enzyme. Four putative ASase genes (bdas, blas, bpas, and btas) were cloned from Bifidobacterium sp. and expressed in Escherichia coli. All ASases from Bifidobacterium sp. (BAS) displayed typical ASase properties with slightly different characteristics. Among the BASs studied, BdAS and BpAS showed maximal enzyme activities at 35 and 30 °C, respectively, whereas BlAS and BtAS were maximally active at higher temperatures, i.e., 45 and 50 °C, respectively. BpAS exhibited optimum pH under slightly basic conditions (pH 8.0), while BdAS, BlAS, and BtAS preferred weakly acidic conditions (pH 5.0-6.0). All BASs showed higher isomerization activities. Particularly, BlAS produced more trehalulose than turanose. Although polymerization was the highest for BtAS, BtAS synthesized α-1, 4-glucans with a lower degree of polymerization than that of the other BASs. The versatile properties of the BASs described could contribute to the efficient production of highly valuable biomaterials for the agriculture, food, and pharmaceutical industries.

Versatile biotechnological applications of amylosucrase, a novel glucosyltransferase

Amylosucrase (AS; EC 2.4.1.4) is an enzyme that has great potential in the biotechnology and food industries, due to its multifunctional enzyme activities. It can synthesize α-1,4-glucans, like amylose, from sucrose as a sole substrate, but importantly, it can also utilize various other molecules as acceptors. In addition, AS produces sucrose isomers such as turanose and trehalulose. It also efficiently synthesizes modified starch with increased ratios of slow digestive starch and resistant starch, and glucosylated functional compounds with increased water solubility and stability. Furthermore, AS produces turnaose more efficiently than other carbohydrate-active enzymes. Amylose synthesized by AS forms microparticles and these can be utilized as biocompatible materials with various bio-applications, including drug delivery, chromatography, and bioanalytical sciences. This review not only compares the gene and enzyme characteristics of microbial AS, studied to date, but also focuses on the applications of AS in the biotechnology and food industries.

Sucrose isomers as alternative sweeteners: properties, production, and applications

In the daily diet, sweeteners play an indispensable role. Among them, sucrose, a widely occurring disaccharide in nature, is a commonly used sweetener. However, the intake of sucrose can cause a rapid increase in blood glucose, which leads to a number of health problems. Therefore, there is an urgent need for possible alternatives to sucrose. Currently, four naturally occurring sucrose isomers, trehalulose, turanose, leucrose, and isomaltulose are considered to be possible alternatives to sucrose due to their suitable sweetness, potential physiological benefits, and feasible production processes. This review covers the properties of these alternative sweeteners, including their structure, sweetness, hydrolysis rate, toxicology, and cariogenicity, and exhibits their potential applications in chronic diseases management, anti-inflammatory supplement, prebiotic dietary supplement, and stabilizing agent. The biosynthesis of these sucrose isomers using carbohydrate-active enzymes and their industrial production processes are also systematically summarized.

Thermostable Amylosucrase from Calidithermus timidus DSM 17022: Insight into Its Characteristics and Tetrameric Conformation

Amylosucrase (EC 2.4.1.4, ASase), a typical carbohydrate-active enzyme, can catalyze 5 types of reactions and recognize more than 50 types of glycosyl acceptors. However, most ASases are unstable even at 50 °C, which limits their practical industrial applications. In this study, an extremely thermostable ASase was discovered from Calidithermus timidus DSM 17022 (CT-ASase) with an optimal activity temperature of 55 °C, half-life of 1.09 h at 70 °C, and melting temperature of 74.47 °C. The recombinant CT-ASase was characterized as the first tetrameric ASase, and a structure-based truncation mutation was conducted to confirm the effect of tetrameric conformation on its thermostability. In addition, α-1,4-glucan was found to be the predominant product of CT-ASase at pH 6.0-8.0 and 30-60 °C.

Characterization of a novel amylosucrase gene from the metagenome of a thermal aquatic habitat, and its use in turanose production from sucrose biomass

Turanose is a natural isomer of sucrose. It is an emerging functional sweetener of the next generation. Turanose is catalytically synthesized from the sucrose biomass by employing amylosucrase enzyme. In this study, a novel gene encoding amylosucrase (As_met) has been identified from the metagenome of a thermal aquatic habitat. As_met exhibits 37-55% identity at the protein level with the known amylosucrases characterized till date. As_met was cloned and expressed in Escherichia coli, followed by protein purification, and characterization. As_met protein exhibited the maximum total activity at 9.0 pH and 60 °C temperature, whereas, 8.0 pH and 50 °C temperature were found optimum for transglycosylation activity. As_met showed fairly high thermal tolerance at 50 °C. The conjugation of As_met protein with functionalized iron nanoparticles significantly improved its thermal tolerance, showing hardly any loss in the enzyme's activity even after 72 h of heat (50 °C) exposure. The turanose yield of about 47% was achieved from 1.5 M sucrose, containing 0.5 M fructose in the reaction. Turanose was purified (˜95%) via a bio-physical process, and characterized by TLC, HPLC, and NMR. The novel amylosucrase gene was demonstrated to be a potential candidate for turanose production, utilizing various sucrose containing feedstocks.

Sucrose-based biosynthetic process for chain-length-defined α-glucan and functional sweetener by Bifidobacterium amylosucrase

A unique thermostable amylosucrase from Bifidobacterium thermophilum was produced as a recombinant protein with the half-life of 577 h at 50 °C. By adding 1.0 M fructose, turanose yield was improved from 22.7% to 43.3% with 1.0 M sucrose, and from 23.7% to 39.4% with 1.5 M sucrose. Sucrose consumption rate was greatest at 55 °C, but the lowest amount of turanose was produced. Thus, turanose yield from sucrose biomass was inversely proportional to reaction temperature and was highly dependent on [fructose]. Meanwhile, insoluble α-glucan yield was clearly reduced as [fructose] increased. With 1.0 M fructose + 1.0 M sucrose, glucan byproduct yield significantly decreased from 29.4% to 1.1%. Molecular weights of linear glucans were almost identical among various [sucrose]s and were homogenous with very low polydispersity. This unique dual reaction patterns of amylosucrase enzyme would be very useful for massive productions of two different biomaterials simply by changing sucrose biomass concentration.

Elucidation of rheological, microstructural, water mobility, and noodle-making properties of rice flour affected by turanose

The effects of turanose on the physicochemical properties of rice flour systems (aqueous suspension, dough, and noodles) were investigated in terms of rheology, microstructure, and water mobility. Inclusion of turanose increased the pasting viscosities of rice flour by maintaining a closely-packed structure at high temperatures that was confirmed by the real-time microscopic measurements during heating. The elevated probability of intergranular interactions by turanose apparently raised both storage (G') and loss (G″) moduli of the rice flour pastes as well as their respective viscosities. NMR spin-spin relaxation times showed two distinct water populations in the turanose-rice flour samples. The Mixolab experiments demonstrated that the rice doughs with higher levels of turanose exhibited greater dough stability as well as higher degrees of starch gelatinization and retrogradation. Furthermore, the extruded rice noodles containing turanose exhibited a higher expansion ratio and a firmer texture that contributed to lowering the cooking loss by 24.5%.

Amylosucrase as a transglucosylation tool: From molecular features to bioengineering applications

Amylosucrase (EC 2.4.1.4, ASase), an outstanding sucrose-utilizing transglucosylase in the glycoside hydrolase family 13, can produce glucans with only α-1,4 linkages. Generally, on account of a double-displacement mechanism, ASase can catalyze polymerization, isomerization, and hydrolysis reactions with sucrose as the sole substrate, and has transglycosylation capacity to attach glucose molecules from sucrose to extra glycosyl acceptors. Based on extensive enzymology research, this review presents the characteristics of various ASases, including their microbial metabolism, preparation, and enzymatic properties, and exhibits structure-based strategies in the improvement of activity, specificity, and thermostability. As a vital transglucosylation tool of producing sugars, carbohydrate-based bioactive compounds, and materials, the bioengineering applications of ASases are also systematically summarized.

Acute and 13-week subchronic toxicological evaluations of turanose in mice

BACKGROUND/OBJECTIVES

Turanose, α-D-glucosyl-(1→3)-α-D-fructose, is a sucrose isomer which naturally exists in honey. To evaluate toxicity of turanose, acute and subchronic oral toxicity studies were conducted with ICR mice.

MATERIALS AND METHODS

For the acute oral toxicity study, turanose was administered as a single oral dose [10 g/kg body weight (b.w.)]. In the subchronic toxicity study, ICR mice were administered 0, 1.75, 3.5, and 7 g/kg b.w. doses of turanose daily for 13 weeks.

RESULTS

No signs of acute toxicity, including abnormal behavior, adverse effect, or mortality, were observed over the 14-day study period. In addition, no changes in body weight or food consumption were observed and the median lethal dose (LD₅₀) for oral intake of turanose was determined to be greater than 10 g/kg b.w. General clinical behavior, changes in body weight and food consumption, absolute and relative organ weights, and mortality were not affected in any of the treatment group for 13 weeks. These doses also did not affect the macroscopic pathology, histology, hematology, and blood biochemical analysis of the mice examined.

CONCLUSION

No toxicity was observed in the acute and 13-week subchronic oral toxicology studies that were conducted with ICR mice. Furthermore, the no-observed-adverse-effect level is greater than 7 g/kg/day for both male and female ICR mice.

Regulation of Inflammation by Sucrose Isomer, Turanose, in Raw 264.7 Cells

Increased sugar consumption has been proposed to be a risk factor for obesity-related metabolic disorders. The objective of this study was to investigate the anti-inflammatory effect of turanose in Raw 264.7 macrophages. Turanose (3-O-α-D-glucosyl-D-fructose), an isomer of sucrose, naturally exists in honey. For these studies, macrophages were treated with total glucose (Glu), 50% Glu/50% turanose (T50), 25% Glu/75% turanose (T75), and 100% turanose (T100), each with a total concentration of 25 mM in cell media. Expressions of inflammatory enzymes and cytokines were analyzed. Cell viability was not affected in the turanose treated groups compared to the Glu group. Lipopolysaccharide and glucose-induced nitric oxide production, protein expression of inducible nitric oxide synthase, COX-2, and superoxide dismutase 2, and mRNA expression levels of interleukin (IL)-1β and IL-18 were significantly suppressed by turanose treatment. These results demonstrate that turanose exerts anti-inflammatory effects in vitro, and possesses potential to serve therapeutic functional sweetener for testing in vivo and in clinical trials.

Identification of an α-(1,4)-Glucan-Synthesizing Amylosucrase from Cellulomonas carboniz T26

Amylosucrase, catalyzing the synthesis of α-(1,4)-glucan from sucrose, has been widely studied and used in carbohydrate biotransformation because of its versatile activities. In this study, a novel amylosucrase was characterized from Cellulomonas carboniz T26. The recombinant enzyme was overexpressed in Escherchia coli and purified by nickel affinity chromatography. It was determined to be a monomeric protein with a molecular mass of 72 kDa. The optimum pH and temperature for transglucosylation were measured to be pH 7.0 and 40 °C. The transglucosylation activity was significantly higher than the hydrolytic activity. The main product generated from sucrose was structurally determined to be α-(1,4)-glucan. A small amount of glucose was produced by hydrolysis, and sucrose isomers including turanose and trehalulose were generated as minor products. The ratio of hydrolytic, polymerization, and isomerization reactions was calculated to be 5.8:84.0:10.2. The enzyme favored production of long-chain insoluble α-glucan at lower temperature.

GH13 amylosucrases and GH70 branching sucrases, atypical enzymes in their respective families

Amylosucrases and branching sucrases are α-retaining transglucosylases found in the glycoside-hydrolase families 13 and 70, respectively, of the clan GH-H. These enzymes display unique activities in their respective families. Using sucrose as substrate and without mediation of nucleotide-activated sugars, amylosucrase catalyzes the formation of an α-(1 → 4) linked glucan that resembles amylose. In contrast, the recently discovered branching sucrases are unable to catalyze polymerization of glucosyl units as they are rather specific for dextran branching through α-(1 → 2) or α-(1 → 3) branching linkages depending on the enzyme regiospecificity. In addition, GH13 amylosucrases and GH70 branching sucrases are naturally promiscuous and can glucosylate different types of acceptor molecules including sugars, polyols, or flavonoids. Amylosucrases have been the most investigated glucansucrases, in particular to control product profiles or to successfully develop tailored α-transglucosylases able to glucosylate various molecules of interest, for example, chemically protected carbohydrates that are planned to enter in chemoenzymatic pathways. The structural traits of these atypical enzymes will be described and compared, and an overview of the potential of natural or engineered enzymes for glycodiversification and chemoenzymatic synthesis will be highlighted.

Enzymatic Process for High-Yield Turanose Production and Its Potential Property as an Adipogenesis Regulator

Turanose is a sucrose isomer naturally existing in honey and a promising functional sweetener due to its low glycemic response. In this study, the extrinsic fructose effect on turanose productivity was examined in Neisseria amylosucrase reaction. Turanose was produced, by increasing the amount of extrinsic fructose as a reaction modulator, with high concentration of sucrose substrate, which resulted in 73.7% of production yield. In physiological functionality test, lipid accumulation in 3T3-L1 preadipocytes in the presence of high amounts of pure glucose was attenuated by turanose substitution in a dose-dependent manner. Turanose treatments at concentrations representing 50%, 75%, and 100% of total glucose concentration in cell media significantly reduced lipid accumulation by 18%, 35%, and 72%, respectively, as compared to controls. This result suggested that turanose had a positive role in controlling adipogenesis, and enzymatic process of turanose production has a potential to develop a functional food ingredient for controlling obesity and related chronic diseases.

Efficient Biocatalytic Production of Cyclodextrins by Combined Action of Amylosucrase and Cyclodextrin Glucanotransferase

A novel enzymatic process for cyclodextrin (CD) production was developed by utilizing sucrose as raw material instead of corn starch. Cyclodextrin glucanotransferase (CGTase) from Bacillus macerans was applied to produce the CDs from linear α-(1,4)-glucans, which were obtained by Neisseria polysaccharea amylosucrase (NpAS) treatment on sucrose. The greatest CD yield (21.1%, w/w) was achieved from a one-pot dual enzyme reaction at 40 °C for 24 h. The maximum level of CD production (15.1 mg/mL) was achieved with 0.5 M sucrose in a simultaneous mode of dual enzyme reaction, whereas the reaction with 0.1 M sucrose was the most efficient with regard to conversion yield. Consequently, dual enzyme synthesis of CDs was successfully carried out with no need of starch material. This result can be applied as a novel efficient bioconversion process that does not require the high temperature necessary for starch liquefaction by thermostable α-amylase in conventional industrial processing.

Distinguishing isomeric aldohexose-ketohexose disaccharides by electrospray ionization mass spectrometry in positive mode

RATIONALE

The identification of the structure of carbohydrates is challenging because of their complex composition of monosaccharide units, linkage position and anomeric configuration. We used a combination of principle component analysis (PCA) and tandem mass spectrometry (MS/MS), including collision-induced dissociation (CID) and higher energy collision dissociation (HCD), to distinguish four aldohexose-ketohexose isomers, sucrose, turanose, maltulose, and palatinose, which are composed of glucose and fructose.

METHODS

The electrospray ionization (ESI)-MS/MS spectra of the lithium and sodium adducts of the glucopyranosyl fructose (Glc-Fru) isomers were recorded on two independent mass spectrometers using CID (MicroTOF QII) and HCD (Q-Exactive Orbitrap). The differences between the fragment ions were evaluated by the PCA models. The glycosidic bond cleavage mechanism of lithiated sucrose was verified by a deuterium-labeling experiment combined with density functional theory calculations (Gaussian 09).

RESULTS

The main fragment ions in the MS/MS spectra from the glycosidic bond decomposition, cross-ring cleavage (-90 Da), and dehydration of the precursor ions of m/z 349 ([M+Li](+)) and m/z 365 ([M+Na](+)) were observed. Surprisingly, cross-ring cleavage and dehydration of the precursor ions were rarely observed in both lithiated and sodiated sucrose. There were significant differences in the fragmentation patterns and relative abundances of fragment ions in second-order mass spectrometry, which allowed discriminant models to be constructed for the alkali adducts and collision modes.

CONCLUSIONS

Glc-Fru isomers were discriminated in the PCA score plots for their lithium and sodium adducts by using different collision modes. The results showed that HCD-MS/MS is an ideal tool for differentiating lithium adducts, whereas, CID-MS/MS is better for discriminating sodium adducts. The hydrogen migration of the hydroxyl group at C3 of the fructose unit caused the glycosidic bond decomposition of lithiated sucrose.

Recycle HPLC: A Powerful Tool for the Purification of Natural Products

Natural compounds occur as various isomeric or closely related structures in biological matrices. These compounds are difficult to separate from the complex mixtures, and hence, the need for effective and innovative separation techniques arises. Recycle HPLC allows the recycling of sample, in part or full, and increases the separation efficiency of the process while keeping the peak dispersion to a minimum. Recycling in an HPLC system has been used in the isolation and purification of different types of natural products including enantiomers, diastereomers, epimers, positional isomers, and structurally related or unrelated compounds having similar retention characteristics. The present paper overviews the development of instrumentation and setup of recycle HPLC and its applications in the separation of natural products.