Enzymatic production and complete nuclear magnetic resonance assignment of the sugar lactulose

One-Pot Three-Enzyme System for Production of a Novel Prebiotic Mannosyl-β-(1 → 4)-Fructose Using a d-Mannose Isomerase from Xanthomonas phaseoli

The present supply of prebiotics is entirely inadequate to meet their demand. To produce novel prebiotics, a d-mannose isomerase (XpMIaseA) from Xanthomonas phaseoli was first produced in Komagataella phaffii (Pichia pastoris). XpMIaseA shared the highest amino acid sequence identity (58.0%) with the enzyme from Marinomonas mediterranea. Efficient secretory production of XpMIaseA (282.0 U mL^-1) was achieved using high cell density fermentation. The optimal conditions of XpMIaseA were pH 7.5 and 55 °C. It showed a broad substrate specificity, which isomerized d-mannose, d-talose, mannobiose, epilactose, and mannotriose. XpMIaseA was employed to construct a one-pot three-enzyme system for the production of mannosyl-β-(1 → 4)-fructose (MF) using mannan (5%, w/v) as the substrate. The equilibrium yield of MF was 58.2%. In in vitro fermentations, MF significantly stimulated (≤3.2-fold) the growth of 12 among 15 tested Bifidobacterium and Lactobacillus strains compared with fructo-oligosaccharides. Thus, the novel d-mannose isomerase provides a one-pot bioconversion strategy for efficiently producing novel prebiotics.

Lactulose production from lactose isomerization by chemo-catalysts and enzymes: Current status and future perspectives

Lactulose, a semisynthetic nondigestive disaccharide with versatile applications in the food and pharmaceutical industries, has received increasing interest due to its significant health-promoting effects. Currently, industrial lactulose production is exclusively carried out by chemical isomerization of lactose via the Lobry de Bruyn-Alberda van Ekenstein (LA) rearrangement, and much work has been directed toward improving the conversion efficiency in terms of lactulose yield and purity by using new chemo-catalysts and integrated catalytic-purification systems. Lactulose can also be produced by an enzymatic route offering a potentially greener alternative to chemo-catalysis with fewer side products. Compared to the controlled trans-galactosylation by β-galactosidase, directed isomerization of lactose with high isomerization efficiency catalyzed by the most efficient lactulose-producing enzyme, cellobiose 2-epimerase (CE), has gained much attention in recent decades. To further facilitate the industrial translation of CE-based lactulose biotransformation, numerous studies have been reported on improving biocatalytic performance through enzyme mediated molecular modification. This review summarizes recent developments in the chemical and enzymatic production of lactulose. Related catalytic mechanisms are also highlighted and described in detail. Emerging techniques that aimed at advancing lactulose production, such as the boronate affinity-based technique and molecular biological techniques, are reviewed. Finally, perspectives on challenges and opportunities in lactulose production and purification are also discussed.

Enzymatic production of lactulose by fed-batch and repeated fed-batch reactor

The effects of the most significant operational variables on reactor performance of fed-batch and repeated fed-batch were evaluated in the lactulose production by enzymatic transgalactosylation. Feed flowrate in the fed stage (F) and fructose to lactose molar ratio (Fr/L) were the variables that mostly affected the values ​​of lactulose yield (Y_Lu), lactulose productivity (π_Lu) and selectivity of transgalactosylation (S_Lu/_TOS). Maximum Y_Lu of 0.21 g lactulose per g lactose was obtained at 50% w/w inlet carbohydrates concentration (IC) of, 50 °C, Fr/L 8, F 1 mL⋅min^-1, 200 IU∙g_Lactose^-1 reactor enzyme load and pH 4.5. At these conditions the selectivity was 7.4, productivity was 0.71 g_Lu∙g^-1∙h^-1and lactose conversion was 0.66. The operation by repeated fed batch increases the efficiency of use of the biocatalysts (E_B) and the accumulated productivity compared to batch and fed batch operation with the same biocatalyst. E_B obtained was 4.13 g_Lu∙mg_{biocatalyst protein}^-1, 10.6 times higher than in fed-batch.

Secretion of a low and high molecular weight β-glycosidase by Yarrowia lipolytica

Background

The secretory production of recombinant proteins in yeast simplifies isolation and purification but also faces possible complications due to the complexity of the secretory pathway. Therefore, correct folding, maturation and intracellular transport of the recombinant proteins are important processing steps with a higher effort needed for complex and large proteins. The aim of this study was to elucidate the secretion potential of Yarrowia lipolytica for low and high molecular weight β-glycosidases in a comparative cultivation approach.

Results

A low sized β-glucosidase from Pyrococcus furiosus (CelB; 55 kDa) and a large sized β-galactosidase isolated from the metagenome (M1; 120 kDa) were integrated into the acid extracellular protease locus using the CRISPR–Cas9 system to investigate the size dependent secretion of heterologous proteins in Y. lipolytica PO1f. The recombinant strains were cultivated in the bioreactor for 78 h and the extra- and intracellular enzyme activities were determined. The secretion of CelB resulted in an extracellular volumetric activity of 187.5 µkat_oNPGal/L_medium, while a volumetric activity of 2.98 µkat_oNPGal/L_medium was measured during the M1 production. However, when the amount of functional intra- and extracellular enzyme was investigated, the high molecular weight M1 (85%) was secreted more efficiently than CelB (27%). Real-time PCR experiments showed a linear correlation between the transcript level and extracellular activity for CelB, while a disproportional high mRNA level was observed regarding M1. Interestingly, mass spectrometry data revealed the unexpected secretion of two endogenous intracellular glycolytic enzymes, which is reported for the first time for Y. lipolytica.

Conclusion

The results of this study provide deeper insights into the secretion potential of Y. lipolytica. A secretion limitation for the low-size CelB was observed, while the large size M1 enzyme was produced in lower amounts but was secreted efficiently. It was shown for the first time that Y. lipolytica is a promising host for the secretion of heterologous high molecular weight proteins (> 100 kDa), although the total secreted amount has to be increased further.

Impact of Amorphization Methods on the Physicochemical Properties of Amorphous Lactulose

The influence of the amorphization technique on the physicochemical properties of amorphous lactulose was investigated. Four different amorphization techniques were used: quenching of the melt, milling, spray-drying, and freeze-drying, and amorphous samples were analyzed by differential scanning calorimetry, NMR spectroscopy, and powder X-ray diffraction analysis. Special attention was paid to the tautomeric composition and to the glass transition of amorphized materials. It was found that the tautomeric composition of the starting physical state (crystal, liquid, or solution) is preserved during the amorphization process and has a strong repercussion on the glass transition of the material. The correlation between these two properties as well as the plasticizing effect of the different tautomers was clarified by molecular dynamics simulations.

Lactulose synergizes with CpG-ODN to modulate epithelial and immune cells cross talk

Lactulose, a non-digestible oligosaccharide and functional food, promotes Bifidobacteria growth. Here we show that lactulose, beyond its prebiotic action, may have direct immunomodulatory effects as well. In synergy with CpG-ODN, a bacterial DNA mimetic, lactulose enhances basolateral concentrations of IFN-γ, IL-10, and galectin-9 in the co-culture model of epithelial and immune cells.

Chemoenzymatic synthesis of sialylated lactuloses and their inhibitory effects on Staphylococcus aureus

Background

Sialylated glycoconjugates play important roles in physiological and pathological processes. However, available sialylated oligosaccharides source is limited which is a barrier to study their biological roles. This work reports an efficient approach to produce sialic acid-modified lactuloses and investigates their inhibitory effects on Staphylococcus aureus (S. aureus).

Methods

A one-pot two-enzyme (OPTE) sialylation system was used to efficiently synthesize sialylated lactuloses. Silica gel flash chromatography column was employed to purify the sialylated products. The purity and identity of the product structures were confirmed with mass spectrometry (MS) and nuclear magnetic resonance (NMR). The inhibitory effect of sialylated lactuloses against S. aureus was evaluated by using microplate assay, fluorescence microscopy, DAPI (4',6-diamidino-2-phenylindole) fluorescence staining and protein leakage quantification.

Results

Neu5Ac-containing sialylated lactuloses with either α2,3- or α2,6-linkages were efficiently synthesized via an efficient OPTE sialylation system using α-2,3-sialyltransferase or α-2,6-sialyltransferase, respectively. Neu5Ac-α2,3-lactulose and Neu5Ac-α2,6-lactulose significantly inhibited the growth of S. aureus. Fluorescence microscopy and DAPI fluorescence staining indicated that the sialylated lactuloses might disrupt nucleic acid synthesis of S. aureus.

Conclusions

Neu5Ac-containing sialylated lactuloses had higher antibacterial activity against S. aureus than non-sialylated lactulose. The inhibitory effect of Neu5Ac-α2,3-lactulose was superior to that of Neu5Ac-α2,6-lactulose. The sialylated lactuloses might inhibit S. aureus by causing cell membrane leakage and disrupting nucleic acid synthesis.

Lactulose production by a thermostable glycoside hydrolase from the hyperthermophilic archaeon Caldivirga maquilingensis IC-167

BACKGROUND

Lactulose has various uses in the food and pharmaceutical fields. Thermostable enzymes have many advantages for industrial exploitation, including high substrate solubilities as well as reduced risk of process contamination.

RESULTS

Enzymatic synthesis of lactulose employing a transgalactosylation reaction by a recombinant thermostable glycoside hydrolase (GH1) from the hyperthermophilic archaeon Caldivirga maquilingensis IC-167 was investigated. The optimal pH for lactulose production was found to be 4.5, while the optimal temperature was 85 °C, before it dropped moderately to 83% at 90 °C. However, the relative activity for lactulose synthesis dropped sharply to 35% at 95 °C. At optimal reaction conditions of 70% (w/w) initial sugar substrates with molar ratio of lactose to fructose of 1:4, 15 U mL^-1 enzyme concentration and 85 °C, the time course reaction produced a maximum lactulose concentration of 108 g L^-1 at 4 h, corresponding to a lactulose yield of 14% and 27 g L^-1  h^-1 productivity with 84% lactose conversion. The transgalactosylation reaction for lactulose synthesis was greatly influenced by the ratio of galactose donor to acceptor.

CONCLUSION

This novel GH1 may be useful for process applications owing to its high activity in very concentrated substrate reaction media and promising thermostability. © 2017 Society of Chemical Industry.

Efficient production of lactulose from whey powder by cellobiose 2-epimerase in an enzymatic membrane reactor

In this study, the gene encoding cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus (CsCE) was successfully expressed in Bacillus subtilis WB800. After the fermentation medium optimization, the activity of recombinant strain was 4.5-fold higher than the original medium in a 7.5L fermentor. The optimal catalytic pH and temperature of crude CsCE were 7.0 and 80°C, respectively. An enzymatic synthesis of lactulose was developed using cheese-whey lactose as its substrate. The maximum conversion rate of whey powder obtained was 58.5% using 7.5 U/mL CsCE. The enzymatic membrane reactor system exhibited a great operational stability, confirmed with the higher lactose conversion (42.4%) after 10 batches. To our best knowledge, this is the first report of lactulose synthesis in food grade strain, which improve the food safety, and we not only realize the biological production of lactulose, but also make good use of industrial waste, which have positive impact on environment.

Duodenal morphometry and small bowel permeability in children with portal hypertension

OBJECTIVE

We prospectively studied children with portal hypertension (PHT) for portal hypertensive duodenopathy (PHTD) and small bowel intestinal permeability (SIP) with the objectives of defining histopathological parameters for PHTD and to find out whether any association existed among structural changes, SIP, and nutritional status.

METHOD

SIP was assessed by using lactulose and mannitol sugar probes in 31 children with PHT (cirrhosis n = 15 and extrahepatic portal venous obstruction n = 16) and 15 healthy children as controls. Morphometric assessment from duodenal biopsies was done in children with PHT. SIP and morphometric parameters were correlated with nutritional status and dietary intake.

RESULTS

Among children with PHT, 48% had PHTD defined as presence of villous atrophy (villous to crypt ratio < 2.5:1), dilated capillaries (capillary diameter > 16.8 μm, capillary area > 151 μm, capillary perimeter > 56 μm), and thickened muscularis mucosae (>22.2 μm). Lactulose excretion alone was increased in children with PHT as compared with healthy children (median %: 0.03, 0.02, and 0.01 for cirrhosis, extrahepatic portal venous obstruction, and controls, respectively [P < 0.01]) signifying increased paracellular permeability in PHT. Children with PHT had significantly lower z scores for height, weight, and triceps skin-fold thickness (<-2SD), whereas no differences were found in dietary intake between patients and controls. Increased SIP, nutritional compromise, and PHTD in our patients had no correlation.

CONCLUSIONS

PHT is often associated with duodenopathy. SIP does occur as a result of increased paracellular permeability. Factors of increased SIP, undernutrition, and PHTD do not have correlation in childhood PHT.

Structural insights into the substrate specificity and transglycosylation activity of a fungal glycoside hydrolase family 5 β-mannosidase

β-Mannosidases are exo-acting glycoside hydrolases (GHs) that catalyse the removal of the nonreducing end β-D-mannose from manno-oligosaccharides or mannoside-substituted molecules. They play important roles in fundamental biological processes and also have potential applications in various industries. In this study, the first fungal GH family 5 β-mannosidase (RmMan5B) fromRhizomucor mieheiwas functionally and structurally characterized.RmMan5B exhibited a much higher activity against manno-oligosaccharides than againstp-nitrophenyl β-D-mannopyranoside (pNPM) and had a transglycosylation activity which transferred mannosyl residues to sugars such as fructose. To investigate its substrate specificity and transglycosylation activity, crystal structures ofRmMan5B and of its inactive E202A mutant in complex with mannobiose, mannotriose and mannosyl-fructose were determined at resolutions of 1.3, 2.6, 2.0 and 2.4 Å, respectively. In addition, the crystal structure ofR. mieheiβ-mannanase (RmMan5A) was determined at a resolution of 2.3 Å. BothRmMan5A andRmMan5B adopt the (β/α)8-barrel architecture, which is globally similar to the other members of GH family 5. However,RmMan5B shows several differences in the loop around the active site. The extended loop between strand β8 and helix α8 (residues 354–392) forms a `double' steric barrier to `block' the substrate-binding cleft at the end of the −1 subsite. Trp119, Asn260 and Glu380 in the β-mannosidase, which are involved in hydrogen-bond contacts with the −1 mannose, might be essential for exo catalytic activity. Moreover, the structure of RmMan5B in complex with mannosyl-fructose has provided evidence for the interactions between the β-mannosidase and D-fructofuranose. Overall, the present study not only helps in understanding the catalytic mechanism of GH family 5 β-mannosidases, but also provides a basis for further enzymatic engineering of β-mannosidases and β-mannanases.

Continuous synthesis of lactulose in an enzymatic membrane reactor reduces lactulose secondary hydrolysis

Newly developed parallel small-scale enzymatic membrane reactors (EMRs) were used to enhance the synthesis of lactulose using β-galactosidase. Under batch operation, the productivity of lactulose decreased abruptly from 2.72 down to 0.04 mg lactulose/(Uenzymeh) over 35 h of reaction. This was presumably caused by the action of β-galactosidase which performed secondary hydrolysis upon the produced lactulose. The continuous operations of an EMR system led to continuous removal of lactulose in the reactors restricting lactulose degradation caused by secondary hydrolysis. Therefore, continuous lactulose syntheses in the EMRs yielded significantly higher specific productivities under "steady state" conditions. Approximately 0.70 and 0.50 mg lactulose/(U enzyme h) for hydraulic residence times of 5 and 7h were reached, respectively. Continuous lactulose synthesis performed in an EMR system conclusively can circumvent the drawbacks (e.g., secondary hydrolysis) of lactulose synthesis encountered in batch operation. It is, therefore, beneficial in terms of enhanced lactulose productivity and reduced enzyme consumption.

Detailed analysis of galactooligosaccharides synthesis with β-galactosidase from Aspergillus oryzae

The synthesis of galactooligosaccharides (GOS) catalyzed by β-galactosidase from Aspergillus oryzae (Enzeco) was studied. Using 400 g/L of lactose and 15 U/mL, maximum GOS yield, measured by HPAEC-PAD, was 26.8% w/w of total carbohydrates, obtained at approximately 70% lactose conversion. No less than 17 carbohydrates were identified; the major transgalactosylation product was 6'-O-β-galactosyl-lactose, representing nearly one-third (in weight) of total GOS. In contrast with previous reports, the presence of at least five disaccharides was detected, which accounted for 40% of the total GOS at the point of maximum GOS concentration (allolactose and 6-galactobiose were the major products). A. oryzae β-galactosidase showed a preference to form β(1→6) bonds, followed by β(1→3) and β(1→4) linkages. Results were compared with those obtained with β-galactosidases from Kluyveromyces lactis and Bacillus circulans. The highest GOS yield and specific productivity were achieved with B. circulans β-galactosidase. The specificity of the linkages formed and distribution of di-, tri-, and higher GOS varied significantly among the three β-galactosidases.

Biotechnological approaches for the production of prebiotics and their potential applications

Worldwide interest in prebiotics have been increasing extensively both as food ingredients and pharmacological supplements, since they have beneficial properties for human health. Prebiotics not only stimulate the growth of healthy bacteria such as bifidobacteria and lactobacilli in the gut but also increase the resistance towards pathogens. In addition to this, they also act as dietary fiber, an energy source for intestinal cells after converting to short-chain fatty acids, a stimulator of immune systems, sugar replacer etc. Moreover, due to heat resistant properties, they are able to maintain their intact form during the baking process and allow them to be incorporated into every day food products. Thus, they can be interesting and useful ingredients in the development of novel functional foods. This review provides comprehensive information about the different biotechnological techniques employed in the production of prebiotics and their potential applications in different areas.

Recombinant production of hyperthermostable CelB from Pyrococcus furiosus in Lactobacillus sp

Lactic acid bacteria (LAB) are used widespread in the food industry as traditional starters for various fermented foods. For recombinant protein production, LAB would be superior with view from the food safety demands since most of them are Generally Recognized As Safe organisms. We investigated the two pSIP expression systems, pSIP403 and pSIP409 (Sørvig et al. 2005), to produce a hyper-thermophilic β-glycosidase (CelB) from Pyrococcus furiosus in Lactobacillus plantarum NC8 and Lactobacillus casei as hosts, respectively. Both lactobacilli harboring the pSIP409-celB vector produced active CelB in batch bioreactor cultivations (MRS medium) while the specific CelB activity of the cell free extract was about 44 % higher with L. plantarum (1,590 ± 90 nkat/mg(protein)) than with L. casei (1,070 ± 66 nkat/mg(protein)) using p-nitrophenyl-β-galactoside (pNPGal) as the substrate. A fed-batch bioreactor cultivation of L. plantarum NC8 pSIP409-celB resulted in a specific CelB activity of 2,500 ± 120 nkat ( pNPGal)/mg(protein) after 28 h. A repeated dosage of the inducer spp-IP did not increase the enzyme expression further. As alternative for the cost intensive MRS medium, a basal whey medium with supplements (yeast extract, Tween 80, NH(4)-citrate) was developed. In bioreactor cultivations using this medium, about 556 ± 29 nkat ( pNPGal)/mg(protein) of CelB activity was achieved. It was shown that both LAB were potential expression hosts for recombinant enzyme production. The pSIP expression system can be applied in L. casei.

Lactulose production from lactose as a single substrate by a thermostable cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus

The conditions for maximum lactulose production from lactose, as a single substrate, by a thermostable recombinant cellobiose-2-epimerase from Caldicellulosiruptor saccharolyticus were determined to be pH 7.5, 80 °C, 700 g l(-1) lactose, and 150 U ml(-1) of enzyme. Under the conditions, the enzyme produced the two bifidus factors lactulose at 408 g l(-1) and epilactose at 107 g l(-1) after 2 h. The yields of lactulose and epilactose from lactose and the productivities of lactulose and epilactose were 58%, 15%, 204 g l(-1) h(-1), and 54 g l(-1) h(-1), respectively. The yield and productivity of both lactulose and epilactose from lactose were 74% and 258 g l(-1) h(-1), respectively. The yield, concentration, and productivity of lactulose in the present study are the highest among enzymatic syntheses. This is the first trial of enzymatic synthesis of lactulose using the single substrate lactose.

Lactulose: production, purification and potential applications

Lactulose a "bifidus factor" is composed of galactose and fructose, which can be produced by the isomerization of lactose. It is a prebiotic carbohydrate which stimulates the growth of health-promoting bacteria in the gastrointestinal tract, such as bifidobacteria and lactobacilli and at the same time inhibits growth of pathogenic bacteria such as Salmonella. It can also be used for the treatment of constipation, hepatic encephalopathy, tumour prevention, and to maintain blood glucose and insulin level. This review provides comprehensive information on the different techniques used for the production of lactulose, purification and analysis. Besides this mechanism of action and its potential applications in food and pharmaceutical industries have also been discussed.