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d -Allulose is a low-calorie sweetener with multiple nutritional functions that can be produced through d -fructose isomerization by ketose 3-epimerase (KEase). l -Ribulose 3-epimerase from Arthrobacter globiformis (AgLRE) is one of the most important enzymes that produce d -allulose; however, its substrate recognition mechanism is unknown. In this study, the crystal structures of AgLRE and its complex with d -allulose and d -fructose were determined. Upon substrate binding, the hydrophobic residues around the active-site entrance move toward the bound substrate. A comparison of AgLRE and other KEase structures revealed that the substrate-binding residues are not the main factors responsible for its marked specificity for d -allulose and d -fructose, but the hydrophobicity of the active site pocket influences substrate recognition. Particularly, the two hydrophobic regions at the active site entrance are the regulatory elements that modulate substrate recognition by AgLRE. This study provides useful information for designing AgLRE to increase its affinity for d -allulose and d -fructose. [Display omitted] • The ketose 3-epimerase active site has a substrate-binding and a hydrophobic site. • The hydrophobicity and size of the hydrophobic pockets vary between species. • Hydrophobic residues are involved in the recognition of d -fructose and d -allulose. • Provides a new perspective on the substrate recognition mechanism of ketose 3-epimerase. [ABSTRACT FROM AUTHOR]

In this study, a new deep eutectic mixture (DEM) was prepared from D-fructose, L-arginine, and urea and characterized by Fourier transform infrared (FT-IR), refractive index measurement, and thermogravimetric analysis (TGA). In continue this mixture was used as a green catalyst to promote the synthesis of three important derivatives of heterocyclic compounds. The highlights of this work include some notable advantages such as ease of the preparation and simple catalytic process, low cost, green reaction conditions, biodegradability of the catalyst, short reaction times, high yields of the products and simple work-up. Also, the catalyst could be recovered easily and reused up to several times without significant loss of catalytic activity. [ABSTRACT FROM AUTHOR]

An efficient solvent mediated & use of metal-free catalyst strategy was developed for synthesis of FDCA over two steps. A simple & economical glucose-hydrothermally carbonized (Glu-HTC) catalyst was prepared and evaluated for synthesis of 2,5-Diformyl furan (DFF) from fructose & 5-hydroxymethylfurfural (HMF) in the 1st step. DFF was then converted to FDCA using Pinnick oxidation in the 2nd step. DFF was obtained in 82% & 86% yields from fructose & HMF respectively whereas FDCA was obtained in 94–95% yield from DFF. FDCA was thus formed in an overall yield of 78% and 81% from fructose & HMF respectively. This strategy eliminated use of expensive noble metals for FDCA synthesis and also intermediates such as HMFCA & FFCA were not observed after the reaction as DFF was completely oxidized to FDCA. [ABSTRACT FROM AUTHOR]

Graphene was successfully isolated by Professors Andre Geim and Kostya Novoselov in 2004. Graphene has attracted considerable research importance for its distinctive properties and potential applications. In this study, low-cost and high blue, yellow, and green photoluminescent (PL) graphene quantum dots (GQDs) were synthesized with deionized water (DI) and D-fructose as precursors by the dehydration method in the presence of hydrochloric acid. Transmission electron microscopy imaging proved the changing size of the GQDs and, by nuclear magnetic resonance spectroscopy, we observed the hydrogen-functionalized GQDs. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the synthesized GQDs were determined, and an energy bandgap was obtained from optical investigations.

In this study, two new deep eutectic mixtures were prepared via combination of D-fructose with urea and L-aspartic acid or L-arginine. After identification, the catalytic activity of these mixtures, was evaluated in the one-pot multi-component synthesis of tetrahydro-1,2,4-triazolo[5,1-b]quinazolin-8(4H)-one derivatives. In the presence of both prepared mixtures the desired products were obtained with high diversity from the reaction of 3-amino-1,2,4-triazole, aromatic aldehydes and dimedone or cyclohexanedione in short reaction times with good yields. The reported methods have notable features such as easy preparation of the catalysts, green processes, cost-effectiveness and simple work-up procedures. Addintionally, the catalysts are easily recoverable and can be recycled up to five times without substantial loss of their activity. [ABSTRACT FROM AUTHOR]

Chitosan (CH) is a very well‐known biopolymer that has been widely used for the development of biomaterials with a wide range of applications in the biomedical field, such as the preparation of hydrogels, owing to its outstanding anti‐inflammatory, antibacterial and antifungal properties, biocompatibility and biodegradability, although they present limited mechanical properties. Chemical crosslinking is one of the most recurrent strategies for the reinforcement of these structures and, above all, crosslinking with natural‐origin compounds that do not compromise their biocompatibility is considered a hot topic in this research field. D‐fructose (F), obtained from the hydrolyzation and further isomerization of starch, an abundant raw material and genipin (G), which is extracted from the fruits of Gardenia jasminoides Ellis are used as natural crosslinkers. Chitosan‐based hydrogels crosslinked with each crosslinking agent are prepared and characterized through Fourier transform infrared (FTIR) spectroscopy, crosslinking and swelling degree determination, rheological, microstructural, and biological studies. The results demonstrate that crosslinking with G is more beneficial for chitosan‐based hydrogels since these samples showed more compact structures and better rheological performance. Additionally, excellent biological in vitro behavior due to the crosslinking with G, unlike that of F. [ABSTRACT FROM AUTHOR]

Abstract Chitosan (CH) is a very well‐known biopolymer that has been widely used for the development of biomaterials with a wide range of applications in the biomedical field, such as the preparation of hydrogels, owing to its outstanding anti‐inflammatory, antibacterial and antifungal properties, biocompatibility and biodegradability, although they present limited mechanical properties. Chemical crosslinking is one of the most recurrent strategies for the reinforcement of these structures and, above all, crosslinking with natural‐origin compounds that do not compromise their biocompatibility is considered a hot topic in this research field. D‐fructose (F), obtained from the hydrolyzation and further isomerization of starch, an abundant raw material and genipin (G), which is extracted from the fruits of Gardenia jasminoides Ellis are used as natural crosslinkers. Chitosan‐based hydrogels crosslinked with each crosslinking agent are prepared and characterized through Fourier transform infrared (FTIR) spectroscopy, crosslinking and swelling degree determination, rheological, microstructural, and biological studies. The results demonstrate that crosslinking with G is more beneficial for chitosan‐based hydrogels since these samples showed more compact structures and better rheological performance. Additionally, excellent biological in vitro behavior due to the crosslinking with G, unlike that of F.

Graphene was successfully isolated by Professors Andre Geim and Kostya Novoselov in 2004. Graphene has attracted considerable research importance for its distinctive properties and potential applications. In this study, low-cost and high blue, yellow, and green photoluminescent (PL) graphene quantum dots (GQDs) were synthesized with deionized water (DI) and D-fructose as precursors by the dehydration method in the presence of hydrochloric acid. Transmission electron microscopy imaging proved the changing size of the GQDs and, by nuclear magnetic resonance spectroscopy, we observed the hydrogen-functionalized GQDs. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the synthesized GQDs were determined, and an energy bandgap was obtained from optical investigations. [ABSTRACT FROM AUTHOR]

Rare sugars attract more and more attention as safe low-calorie sweeteners and functional compounds in the food, pharmaceutical and medical industries. D-Allulose, first discovered in wheat over 70 years ago, has significant application potential but its widespread use is limited by high production costs. The epimerization reactions of available sugars resulting in D-allulose production are catalyzed by enzymes of the epimerase group, ketose-3-epimerases. The key tasks of the study of the ketose-3-epimerases family enzymes are defining the exact mechanisms of their action, the improvement of enzymatic activity and stability in order to achieve a higher efficiency of D-allulose production. The review summarizes the latest innovations in the use of ketose-3-epimerases and optimization of D-allulose manufacturing processes. The structural features of the main enzymes explored in the production of the rare sugar, molecular modifications of biocatalysts, and prospects for the practical use of discussed in this work enzyme pathways are also considered. [ABSTRACT FROM AUTHOR]

Novel BF2‐β‐diketonate complexes 1–4 bearing phenylboronic acid moieties and methoxyphenyl or dimethylaminophenyl groups were synthesized and their photophysical properties, pH response, and reactivity to D‐fructose were evaluated. Complexes 1 and 2 bearing a methoxyphenyl group luminesced with high intensity in a range of non‐polar to polar solvents, except in DMSO, whereas complexes 3 and 4 containing a dimethylaminophenyl group with twisted intramolecular charge transfer (TICT) properties showed a dramatic decrease in luminescence intensity with increasing solvent polarity. The luminescence intensity of complexes 1 and 2 decreased with increasing pH due to intermolecular vibration which associated with hydrogen bonding between the complexes and solvent water molecules, whereas it increased when they reacted with D‐fructose due to the suppression of the intermolecular vibration. In contrast, the luminescence intensity of complexes 3 and 4 increased with increasing pH and upon reaction with D‐fructose due to the loss of its TICT properties. The photophysical properties of complexes 1–4 and the TICT properties of complexes 3 and 4 were supported by density functional theory calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Basicity of an amine is the major factor determining catalytic activity. • Catalytic activity in DMSO and DMF is higher than in water and methanol. • Fructofuranose and -pyranose isomerize into allulose and glucose, respectively. • Solvents impact selectivity by influencing tautomeric equilibrium of fructose. • Operando NMR to explore the reaction. Rational catalyst design and optimal solvent selection are key to advancing biorefining. Here, we explored the organocatalytic isomerization of d- fructose to a valuable rare monosaccharide, d- allulose, as a function of solvent. The isomerization of d- fructose to d- allulose competes with its isomerization to d- glucose and sugar degradation. In both water and DMF, the catalytic activity of amines towards d- fructose is correlated with their basicity. Solvents impact the selectivity significantly by altering the tautomeric distribution of d- fructose. Our results suggest that the furanose tautomer of d- fructose is isomerized to d- allulose, and the fractional abundance of this tautomer increases as follows: water < MeOH < DMF ≈ DMSO. Reaction rates are also higher in aprotic than in protic solvents. The best d- allulose yield, 14 %, was obtained in DMF with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst. The reaction kinetics and mechanism were explored using operando NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Exhaled breath condensate (EBC) as a test material in metabolomic studies continues to receive the attention of analysts. The exhaled air condensate is a sample whose composition reflects the characteristics of biochemical processes in the body; this is a relatively pure matrix, as compared to blood, which contains more polar components (including nonvolatile ones) unlike exhaled air. In addition, EBC sampling is noninvasive. The silylation products of lyophilized EBC samples from healthy volunteers and patients with bronchial asthma (BA) and chronic obstructive pulmonary disease (COPD) were studied using gas chromatography–mass spectrometry with electron ionization. The total ion current chromatograms corresponding to the samples of BA and COPD patients exhibited silyl derivatives of mono-D-fructose and disaccharides. It was hypothesized that D-fructose can be a marker of biochemical processes occurring in the patients diagnosed with BA and COPD. [ABSTRACT FROM AUTHOR]

Melanoidins can be diagnosed using the Fourier transform infrared (FTIR) technique. UV/Vis is an effective tool for both qualitative and quantitative analysis of chemical components in melanoidin polymers. The structural and vibrational features of melanoidin synthesized from D-glucose and D-fructose are identical, according to FTIR spectra, with the only difference being the intensity of bands. Using FTIR spectra, the skeleton of melanoidin is divided into seven major regions. The existence of the C=C, C=N, and C=O groups in all melanoidins formed from fructose and glucose with ammonia is confirmed by the areas ranging from 1600 to 1690 cm-1,and the band is largely evident as a broad shoulder. Both melanoidins have a carboxyl or carbonyl extending around 1700 cm-1 . In all melanoidins, the NH+ group has vanished in the 3080 cm-1 range. However, the color intensity depends on the type of sugar employed in melanoidin synthesis. Furthermore, in comparison to Glc-ammonia, which has a higher proportion of sp³ hybridized carbon, Fru-ammonia has a higher proportion of sp² hybridized carbon based on UV/Vis, FTIR and secondderivative spectra. Moreover, the data were simulated using principal component analysis. Principal component analysis (PCA) was used to interpret the data. [ABSTRACT FROM AUTHOR]

d-allulose is a rare low-calorie sugar that has many fundamental biological functions. d-allulose 3-epimerase from Agrobacterium tumefaciens (AT-DAEase) catalyzes the conversion of d-fructose to d-allulose. The enzyme has attracted considerable attention because of its mild catalytic properties. However, the bioconversion efficiency and reusability of AT-DAEase limit its industrial application. Magnetic metal–organic frameworks (MOFs) have uniform pore sizes and large surface areas and can facilitate mass transport and enhance the capacity for enzyme immobilization. Here, we successfully encapsulated cobalt-type AT-DAEase into the cobalt-based magnetic MOF ZIF-67@Fe3O4 using a self-assembly strategy. We confirmed the immobilization of enzyme AT-DAEase and characterized the enzymatic properties of the MOF-immobilized AT-DAEase@ZIF-67@Fe3O4. The AT-DAEase@ZIF-67@Fe3O4 nanoparticles had higher catalytic activity (65.1 U mg−1) and bioconversion ratio (38.1%) than the free AT-DAEase. The optimal conditions for maximum enzyme activity of the AT-DAEase@ZIF-67@Fe3O4 nanoparticles were 55 °C and pH 8.0, which were significantly higher than those of the free AT-DAEase (50 °C and pH 7.5). The AT-DAEase@ZIF-67@Fe3O4 nanoparticles displayed significantly improved thermal stability and excellent recycling performance, with 80% retention of enzyme activity at a temperature range of 45–70 °C and > 45% of its initial activity after eight cycles of enzyme use. The AT-DAEase@ZIF-67@Fe3O4 nanoparticles have great potential for large-scale industrial preparation of d-allulose by immobilizing cobalt-type AT-DAEase into magnetic MOF ZIF-67@Fe3O4. [ABSTRACT FROM AUTHOR]

The robust use of osmolytes (i.e., polyols and sugars) in the key therapeutic regimens/formulations has questioned their impact beyond the stability of therapeutic proteins as these osmolytes trigger structural alterations into proteins including misfolding and subsequent aggregation into amyloid fibrils. Therefore, the current study is the first to delineate the inhibitory effect of carvacrol (CRV) on the carbonyl osmolyte-induced aggregation as well as structural alterations to the bovine serum albumin (BSA) via a set of physicochemical as well as artificial intelligence (AI)-based molecular docking studies. Our initial findings from physicochemical investigations revealed that CRV exhibits substantial protection to BSA under carbonyl osmolyte stress as evident by the compromised hyperchromicity, Schiff's bases, carbonyl and hydroxymethyl furfural content, reduced fluorescent signals, low Rayleigh scattering and prevention of covalent modifications at Lys and Arg residues. The protection against aggregate formation by CRV was further confirmed through the reduced amyloid-specific congo red absorbance as well as fluorescent signals recorded after adding the fibril-specific extrinsic fluorophore probes (i.e., ThT and ANS). The AI-based molecular docking analysis further revealed that CRV (ΔG: −4.96 kcal/mol) competes with d -fructose (ΔG: −4.40 kcal/mol) to mask the Lys and Arg residues to restrict the osmolyte-mediated protein modifications. In conclusion, CRV exhibits substantial protective impact against carbonyl osmolyte-induced structural alterations and protein misfolding and aggregation. [ABSTRACT FROM AUTHOR]

Fructose is widely used in food and beverage industries as a sweetener. In this study, solubility data of fructose in aqueous ethanol (50, 60, 70, 80, and 90 % w/w) at 25, 35, and 45°C were experimentally investigated. With the increase in the ethanol concentration the solubility decreased while with the increase in temperature the solubility increased. Dissolution enthalpy was determined according to the van’t Hoff plot. It was found that the enthalpy linearly increased with the ethanol concentration. Additionally, an empirical solubility model was developed to estimate fructose solubility and validated with literature data. The model gave different root mean square errors (RMSE) for different sets of literature data, but overall, the model can estimate the solubility of fructose (mass fraction) with relatively high accuracy with RMSE of 0.056. [ABSTRACT FROM AUTHOR]

d-Tagatose is a highly promising functional sweetener known for its various physiological functions. In this study, a novel tagatose 4-epimerase from Thermoprotei archaeon (Thar-T4Ease), with the ability to convert d-fructose to d-tagatose, was discovered through a combination of structure similarity search and sequence-based protein clustering. The recombinant Thar-T4Ease exhibited optimal activity at pH 8.5 and 85 °C, in the presence of 1 mM Ni 2+ . Its k cat and k values toward d-fructose were measured to be 248.5 min cat / K m values toward d-fructose were measured to be 248.5 min -1 value of 198 h at 80 °C. Moreover, it achieved a conversion ratio of 18.9% using 100 g/L d-fructose as the substrate. Finally, based on sequence and structure analysis, crucial residues for the catalytic activity of Thar-T4Ease were identified by molecular docking and site-directed mutagenesis. This research expands the repertoire of enzymes with C4-epimerization activity and opens up new possibilities for the cost-effective production of d-tagatose from d-fructose.-1 ·min -1 , respectively. Notably, Thar-T4Ease exhibited remarkable thermostability, with a t 1/2 value of 198 h at 80 °C. Moreover, it achieved a conversion ratio of 18.9% using 100 g/L d-fructose as the substrate. Finally, based on sequence and structure analysis, crucial residues for the catalytic activity of Thar-T4Ease were identified by molecular docking and site-directed mutagenesis. This research expands the repertoire of enzymes with C4-epimerization activity and opens up new possibilities for the cost-effective production of d-tagatose from d-fructose.

Herein, a robust catalytic system was developed for the green synthesis of 5‐methylfurfural (5‐MF) by iodide‐mediated transfer hydrogenation. Around 50 % of 5‐MF was yielded from d‐fructose within 7.5 min using NaI as the catalyst and formic acid as both the hydrogen source and co‐catalyst. The catalytic system was used for six consecutive cycles without any decrease in the yield. Various starch and raw biomass could be used as promising starting materials for 5‐MF synthesis with moderate yields, and the productivity of 5‐MF from corn starch reached 103 mmol gcat−1 h−1, which is comparable with the best result from l‐rhamnose. Moreover, the co‐production of 5‐MF and furfural from raw biomass makes this methodology more competitive than other routes. [ABSTRACT FROM AUTHOR]

We found a putative dolichol phosphate mannose synthases (DPMS) from Bacillus sp., which exhibited the highest specific activity toward d-allulose, one of a functional rare sugars and also known as d-psicose, and identified it as d-allulose 3-epimerase (Basp_DAEase). The gene of Basp_DAEase from Bacillus sp. was cloned to the expression vector (pET-28a(+)) and then expressed as a recombinant enzyme in the Escherichia coli BL21(DE3). The recombinant enzyme was purified homogeneously on the SDS-PAGE with 34 kDa by 6XHis-tagging affinity chromatography and it was found to exist in dimer form as its activity form by Sephacryl S 200 HR 16/60 gelfiltration chromatography. The reaction conditions for a recombinant Basp_DAEase were optimized to produce d-allulose from d-fructose. The epimerization activity of Basp_DAEase toward d-fructose was maximum at pH 7.5 and 40°C with 1 mM Co2+. The half-lives of Basp_DAEase at 35°C, 40°C, 45°C, 50°C, and 55°C were 45.8, 4.18, 1.24, 0.46, and 0.17 h, respectively. At pH 7.5, 40°C, and 1mM Co2+, 215 g/L of d-allulose was produced from 700 g/L of d-fructose by 20 U/mL of Basp_DAEase after 50 min of enzyme reaction with a conversion yield of 31% and productivity of 258 g/L/h. This is the highest productivity of d-allulose from d-fructose reported to date. From this result, it is strongly suggested that Basp_DAEase has high potential application value in the industrial d-allulose production from d-fructose. [ABSTRACT FROM AUTHOR]

The main objective of this work was to found the different sugar adsorption on teeth surface and to obtain information about the process adsorption, such as equilibrium and kinetics process. First, synthetic aqueous solution from different milk solution (100ml) and the concentration (0.05) of stock solution such as glucose was diluted by distilled water from (0.04,0.03,0.02 and 0.01M) and (0.005M) for D-fructose and (0.17M) for raw sugar cubes and using (25 ml) from each solution of different sugars were shaken with (19.5 g) of teeth surface at different temperatures and at pH= 7 for (15 min) and measured the absorbance for these solutions before and after adsorption. When reached the contact time between the adsorbate and adsorbent in adsorption process after 15 minutes and from the amounts adsorbed on teeth, it was described under the Freundlich adsorption isotherms. In conclusion, the factors influencing for the adsorption process such as adsorbent dosage, contact time and temperature and found that the adsorption capacity was increased with increasing initial sugars concentrations and showed that the adsorption increased by increased temperature. Also, studied the thermodynamic parameters such as ÄHo, ÄSo and ÄGo which indicated that the adsorption was endothermic nature and physical adsorption. [ABSTRACT FROM AUTHOR]

The thermodynamics data of crystalline states of two representative components in blood sugar, d-glucose and d-fructose, are significant in researching artificial synthesis and composition transformation in vivo. The heat capacities of d-glucose and d-fructose over a temperature range of 1.9–300 K were measured and calculated by the heat capacity measurement module of physical property measurement system (PPMS). The heat capacities of two compounds increased steadily with temperature, showing a smooth curve without any thermal anomalies. The heat capacity of d-glucose is greater than that of d-fructose in the range of 0 K < T < 80 K, which is smaller than that of d-fructose between 80 and 300 K. Based on the lattice vibration mode, factors of generating the difference heat capacity data between the two isomers were investigated. Additionally, the heat capacity data were fitted by low-temperature heat capacity theoretical model. The thermodynamic data that molar entropy change and molar enthalpy change over the temperature range of 0–300 K were calculated. The standard molar entropy of d-glucose and d-fructose at 298.15 K was calculated by heat capacity fitting to be 214.64 and 217.56 J K−1 mol−1, all with an error of 0.21. [ABSTRACT FROM AUTHOR]

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5-Hydroxymethyl-2-furfurylamine (5-HMFA) as an important 5-HMF derivative has been widely utilized in the manufacture of diuretics, antihypertensive drugs, preservatives and curing agents. In this work, an efficient chemoenzymatic route was constructed for producing 5-(hydroxymethyl)furfurylamine (5-HMFA) from biobased D-fructose in deep eutectic solvent Betaine:Glycerol–water. The introduction of Betaine:Glycerol could greatly promote the dehydration of D-fructose to 5-HMF and inhibit the secondary decomposition reactions of 5-HMF, compared with a single aqueous phase. D-Fructose (200 mM) could be catalyzed to 5-HMF (183.4 mM) at 91.7% yield by SG(SiO2) (3 wt%) after 90 min in Betaine:Glycerol (20 wt%), and at 150 °C. E. coli AT exhibited excellent bio-transamination activity to aminate 5-HMF into 5-HMFA at 35 °C and pH 7.5. After 24 h, D-fructose-derived 5-HMF (165.4 mM) was converted to 5-HMFA (155.7 mM) in 94.1% yield with D-Ala (D-Ala-to-5-HMF molar ratio 15:1) in Betaine:Glycerol (20 wt%) without removal of SG(SiO2), achieving a productivity of 0.61 g 5-HMFA/(g substrate D-fructose). Chemoenzymatic valorization of D-fructose with SG(SiO2) and E. coli AT was established for sustainable production of 5-HMFA, which has potential application.

The sulfonated H‐β zeolite was successfully prepared and used for the synthesis of levulinic acid (LA) from D‐fructose. The catalyst was characterized by powder X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, N2 physisorption, NH3‐temperature programmed desorption and carbon–hydrogen–nitrogen–sulfur analysis. The total acid amount is increased with increase in sulfur loading, confirmed that the sulfonic acid group (SO3‐H) is successfully grafted onto zeolite structure. The various parameters such as different amount of sulfur loading, reaction temperature, time, catalyst loading was studied for selective production of LA. The catalytic activity of sulfonated H‐β (S‐β) zeolite was found to be efficient for synthesis of LA from D‐fructose in aqueous media. Maximum LA yield of 43.5 mol%, low HMF yield (<1%) with 98.15% fructose conversion was obtained with 3% S‐β catalyst at 160°C for 7 hr. The catalyst was reusable for minimum three times by H2O2 regeneration. This study provides the new zeolitic catalyst for the efficient production of LA at shorter reaction time (7 hr) and low catalyst to substrate ratio (0.7:1). [ABSTRACT FROM AUTHOR]

Objective: To develop a method combining enzymatic catalysis and resting-cell biotransformation to produce allitol from low cost substrate d-glucose. Results: The recombinant E. coli expressing d-psicose-3-epimerase (DPE), ribitol dehydrogenase (RDH) and formate dehydrogenase (FDH) for allitol production from d-fructose was constructed. The optimizations of the cell catalytic conditions and the cell cultivation conditions were made. Then, 63.4 g allitol L−1 was obtained from 100 g d-fructose L−1 in 4 h catalyzed by the recombinant E. coli cells. In order to decrease the substrate cost, d-glucose was used as the substrate instead of d-fructose and immobilized glucose isomerase was used to convert d-glucose into d-fructose. In order to simplify allitol production process from d-glucose, one-pot reaction using the mixed catalysts was used and the reaction conditions were optimized. Finally, 12.7 g allitol L−1 was obtained from 50 g d-glucose L−1 catalyzed by the mixed catalysts of immobilized glucose isomerase and the recombinant E. coli cells. Conclusions: Allitol can be efficiently produced from low cost substrate d-glucose by using the method combining enzymatic catalysis and resting-cell biotransformation, which is the first report. [ABSTRACT FROM AUTHOR]

Allitol is a kind of rare sugar alcohol with potential application value. An engineered strain, which simultaneously expressed d-psicose-3-epimerase (DPE), ribitol dehydrogenase (RDH), and formate dehydrogenase (FDH) three enzymes, was constructed by cloning above three genes into one plasmid and transformed into the host E. coli strain, and used as the whole-cell catalysts for biotransformation of allitol from the low-cost substrate of d-fructose. The whole cell allitol biotransformation conditions were optimized. The medium, recombinant gene induction conditions, and the substrate feeding rate for cultivation of the catalytic cells were optimized. Then, the fed-batch culture was made and scaled up to 10 L fermentor. Finally, 63.44 g/L allitol was obtained from 100 g/L d-fructose after 3 h of biotransformation, and the allitol crystals of 99.9% purity were obtained by using cooling recrystallization. The allitol production method developed in this research has high product purity, and is highly efficient, easily scaled up, and suitable for large-scale production of highly purified allitol. [ABSTRACT FROM AUTHOR]

The present work was undertaken to ascertain whether IL-metal salt catalyzed isopropylidenation of d-fructose yield desired acetonides. For the first time, an imidazole based ionic liquid compound accompanied with strontium chloride has been identified as a suitable dual catalyst system for the chemoselective O-isopropylidenation of d-fructose with acetone. In the present protocol, mainly the kinetically controlled less stable cyclic ketal 1,2;4,5-di-O-isopropylidene-β-d-fructopyranose is formed as an initial product with satisfactory yield and without isomerization to the thermodynamically more stable cyclic ketal 2,3;4,5-di-O-isopropylidene-β-d-fructopyranose. Therefore, this protocol is more advantageous compared to other mineral acid catalyzed protocols that require more sensitive reaction conditions. [ABSTRACT FROM AUTHOR]

Stereocontrolled synthesis of rare sugar derivatives, namely α- d -allulofuranosides, was achieved using d -fructose, one of the most abundant carbohydrates in nature. The following are the key steps of the α- d -allulofuranosides' synthesis. (1) An α-selective glycosidation reaction of 1,3,4,6-tetra- O -benzoylated d -fructofuranosyl donor to obtain α- d -fructofuranosides with 98 %–75 % isolated yields. (2) A regioselective 1,4,6-tri-O-pivaloylation reaction of the tetraol of α- d -fructofuranosides with the C3-hydroxy group remaining intact. (3) The oxidation of the C3-hydroxy group followed by the stereoselective reduction of the C3-carbonyl group. Primary and secondary alcohols and sugars can be used as glycosyl acceptors and aglycones for the following pivaloylation and stereoinversion reactions to obtain α- d -allulofuranosides. [Display omitted] • Rare sugar derivative, α- d -allulofuranoside, has been synthesized from d -fructose. • Glycosidation of d -fructofuranosyl donor produces α- d -fructofuranoside selectively. • Regioselective 1,4,6-tri- O -pivaloylation of α- d -fructofuranoside has been achieved. • Stereoinversion at C3–OH of α- d -fructofuranoside provides α- d -allulofuranoside. [ABSTRACT FROM AUTHOR]

Due to the increasing demand for health-conscious and environmentally friendly products, D-mannose has gained significant attention as a natural, low-calorie sweetener. The use of D-mannose isomerases (D-MIases) for D-mannose production has emerged as a prominent area of research, offering superior advantages compared with conventional methods such as plant extraction and chemical synthesis. In this study, a gene encoding D-MIase was cloned from Bifidobacterium and expressed in E. coli BL21 (DE3). The heterologously expressed enzyme, Bifi-mannose, formed a trimer with a molecular weight of 146.3 kDa and a melting temperature (T m) of 63.39 ± 1.3 °C. Bifi-mannose exhibited optimal catalytic activity at pH 7.5 and 55 °C, and retained more than 80% of its activity after a 3-hour incubation at 55 °C, demonstrating excellent thermal stability. The K m , V max , and k cat / K m values of Bifi-mannose for D-fructose isomerization were determined as 538.7 ± 62.5 mM, 11.7 ± 0.9 μmol·mg 1·s 1, and 1.02 ± 0.3 mM 1·s 1, respectively. Notably, under optimized conditions, catalytic yields of 29.4, 87.1, and 148.5 mg·mL 1 were achieved when using 100, 300, and 500 mg·mL 1 of D-fructose as substrates, resulting in a high conversion rate (29%). Furthermore, kinetic parameters and molecular docking studies revealed that His387 residue primarily participates in the opening of the pyranose ring, while His253 acts as a basic catalyst in the isomerization process. [Display omitted] • A novel D-mannose isomerase from Bifidobacterium was biochemically characterized. • Bifi-MIase had a homo-trimeric structure and was quite stable at 55 °C. • A high conversion rate (29%) was achieved using Bifi-MIase to produce d-mannose. • Molecular simulation depicted the presumed catalysis mechanism of Bifi-MIase. [ABSTRACT FROM AUTHOR]

Abstract Background d-Tagatose 3-epimerase epimerizes d-fructose to yield d-psicose, which is a rare sugar that exists in small quantities in nature and is difficult to synthesize chemically. We aim to explore potential industrial biocatalysts for commercial-scale manufacture of this rare sugar. A d-tagatose 3-epimerase from Rhodobacter sphaeroides (RsDTE) has recently been identified as a d-tagatose 3-epimerase that can epimerize d-fructose to yield d-psicose with a high conversion rate. Results The purified RsDTE by Ni-affinity chromatography, ionic exchange chromatography and gel filtration forms a tetramer in solution. The maximal activity was in Tris–HCl buffer pH 8.5, and the optimal temperature was at 35 °C. The product, d-psicose, was confirmed using HPLC and NMR. Crystals of RsDTE were obtained using crystal kits and further refined under crystallization conditions such as 10% PEG 8000,0.1 M HEPES pH 7.5, and 8% ethylene glycol at 20 °C using the sitting-drop vapor diffusion method. The RsDTE homology model showed that it possessed the characteristic TIM-barrel fold. Four residues, Glu156, Asp189, Gln215 and Glu250, forms a hydrogen bond network with the active Mn(II) for the hydride transfer reaction. These residues may constitute the catalytic tetrad of RsDTE. The residues around O1, O2 and O3 of the substrates were conserved. However, the binding-site residues are different at O4, O5 and O6. Arg118 formed the unique hydrogen bond with O4 of d-fructose which indicates RsDTE’s preference of d-fructose more than any other family enzymes. Conclusions RsDTE possesses a different metal-binding site. Arg118, forming unique hydrogen bond with O4 of d-fructose, regulates the substrate recognition. The research on d-tagatose 3-epimerase or d-psicose 3-epimerase enzymes attracts enormous commercial interest and would be widely used for rare sugar production in the future.

• High Cu-Ni interaction was achieved through coprecipitation-deposition over SiO 2 at constant pH. • CuNi/SiO 2 has better catalytic performance than the corresponding monometallic catalysts. • Synergy between Cu and Ni improves catalytic performance in aqueous-phase fructose hydrogenation. • Original catalytic activity of CuNi/SiO 2 can be recovered by treatment under H 2 flow at 773 K. D-fructose hydrogenation in aqueous phase, at 373 K and 40 bar, was performed using monometallic and bimetallic Cu-Ni/SiO 2 catalysts prepared by precipitation-deposition at controlled pH, without any type of co-catalysts and/or additives in solution. The precursors and catalysts were characterized by X-ray diffraction (XRD), N 2 physisorption at 77 K, temperature programmed reduction (TPR), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS) analysis, temperature programmed desorption of H 2 (H 2 -TPD) and X-ray photoelectron spectroscopy (XPS). The characterization of the mono and bimetallic samples showed that metal phase is composed of nanoparticles highly dispersed on SiO 2 surface. It was also found evidence that a Cu-Ni like-alloy forms in the bimetallic sample. Precisely, the best catalytic performance was obtained with the bimetallic catalyst. This was attributed to a synergistic effect between Cu and Ni, favored by the intimate contact between both elements, which was reached from the Cu-Ni coprecipitation at controlled pH over SiO 2. In a three cycles experiment performed with CuNi/SiO 2 , partial catalyst deactivation was observed. The original activity could be recovered by ex-situ reduction under H 2 flow. By temperature programmed oxidation (TPO), it was found that this deactivation is due to surface carbon species strongly chemisorbed on the metallic phase. [ABSTRACT FROM AUTHOR]

• A novel D-LI was characterized from Thermoflavimicrobium dichotomicum. • It was strictly metal-dependent and showed maximum activity at 60 °C and pH 7.5. • Equilibrium ratio of d -mannose and d -fructose was measured to be 25:75. • From 500 g/L of d -fructose, 110.5 g/L of d -mannose was produced by T. dichotomicum D-LI. d -Mannose is the aldose isomer of d -fructose and displays unique physiological functions and health applications. As a result, it has attracted increasing interest from the public. Because of its wide substrate specificity, d -lyxose isomerase (D-LI) has been applied to d -mannose bioproduction. In this article, the Thermoflavimicrobium dichotomicum D-LI encoding gene was cloned and overexpressed in Escherichia coli BL21(DE3). The novel protein T. dichotomicum D-LI was identified and characterized, and its maximum enzyme activity was exhibited at pH 7.5 (phosphate buffer) and 60 °C in the presence of Mn2+. Similar to other D-LIs, T. dichotomicum D-LI formed a homodimeric structure and showed strict conservation of the metal coordination and substrate binding sites. The D-LI half-life (t 1/2) was 9.91 h and 3.05 h at 55 and 60 °C, respectively, and its melting temperature (T m) was 72.85 °C. T. dichotomicum D-LI displayed the highest specific activity towards d -lyxose among the substrates tested, followed by d -mannose. It also efficiently converted d -fructose to d -mannose, and the equilibrium ratio between d -mannose and d -fructose during T. dichotomicum D-LI activity was 25:75. From 500 g/L d -fructose, 110.5 g/L d -mannose was produced after 6 h, suggesting that T. dichotomicum D-LI might provide an alternative for d -mannose production. [ABSTRACT FROM AUTHOR]

d-Allulose is a rare monosaccharide that exists in extremely small quantities in nature, and it is also hard to prepare at a large scale via chemical or enzyme synthetic route due to low conversion and downstream separation complexity. Using d-psicose epimerase and l-rhamnulose kinase, a method enabling high conversion of d-allulose from d-fructose without the need for a tedious isomer separation step was established recently. However, this method requires expensive ATP to facilitate the reaction. In the present study, an ATP regenerate system was developed coupling with polyphosphate kinase. In our optimized reaction with purified enzymes, the conversion rate of 99% d-fructose was achieved at the concentrations of 2 mM ATP, 5 mM polyphosphate, 20 mM d-fructose, and 20 mM Mg2+ when incubated at 50 °C and at pH 7.5. ATP usage can be reduced to 10% of the theoretical amount compared to that without the ATP regeneration system. A fed-batch mode was also studied to minimize the inhibitory effect of polyphosphate. The biosynthetic system reported here offers a potential and promising platform for the conversion of d-fructose into d-allulose at reduced ATP cost. [ABSTRACT FROM AUTHOR]

Most monosaccharides in nature are hexoses, which have six carbon atoms; the most well-known hexose is D-glucose. Various hexoses with distinct characteristics can be produced from inexpensive polysaccharides for applications in the food industry. Therefore, identification of the health-related functions of hexose will facilitate the consumption of hexoses in food products to improve quality of life. The hexoses available in foods include N-acetyl glucosamine, D-glucosamine, D-fructose, D-mannose, D-galactose, other D-hexoses, and l-hexoses. Here, an updated overview of food industrial production methods for natural hexoses by microbial, enzymatic, and chemical methods is provided. [ABSTRACT FROM AUTHOR]

In this research work, we measured the refractive indices for aqueous solutions of ethylene glycol, D-mannitol, D-fructose, sucrose, and maltose at T = 294.15, 298.15, and 303.15 K and atmospheric pressure entire wide range of molar concentrations. These measurements were done in order to investigate the power of interactions between solute and solvent molecules as well as the effect of temperature in these interactions. For these mixtures, the experimental values of refractive index were correlated with experimental equation and constants of this equation (Kr) were applied to investigate on power of interactions between solute species in solutions of this study. [ABSTRACT FROM AUTHOR]

The scarcity, richness, and other important physiological functions of D-psicose make it crucial to increase the yield of D-psicose. The production of D-psicose can be accomplished by D-psicose 3-epimerase (DPEase) from Clostridium bolteae (CbDPEase) catalyzing the substrate D-fructose. Although the catalytic efficiency of the CbDPEase has been raised via using the site-directed mutagenesis (Y68I/G109P) technique, structure-activity relationship in the wild-type CbDPEase and Y68I/G109P mutant is currently poorly understood. In our study, a battery of molecular modeling methods [homology modeling, adaptive steered molecular dynamics (ASMD) simulations, and Molecular Mechanics/Generalized Born Surface Area (MM-GB/SA)], combined with protein structure networks, were employed to theoretically characterize the reasons for the differences in the abilities of the D-fructose catalyzed by the wild-type CbDPEase and Y68I/G109P mutant. Protein structure networks demonstrated that site-directed mutagenesis enhanced the connectivity between D-fructose and CbDPEase, leading to the increased catalytic efficiency mediated by the functional residues with high betweenness. During the dissociation of the D-fructose from the Y68I/G109P mutant, planes of benzene rings of F248 and W114 could be continuously parallel to the stretching direction of D-fructose. It made the tunnel have an open state and resulted in the stable donor-π interactions between D-fructose and the benzene rings around 18Å. The stronger substrate-protein interactions were detected in the Y68I/G109P mutant, instead of in the wild-type CbDPEase, which were consistent with the binding free energy and Potential Mean of Force (PMF) results. The theoretical results illustrated the reasons that Y68I/G109P mutations increased the catalytic efficiency of CbDPEase and could be provided the new clue for further DPEase engineering.

This study aims to analyse the pH value on Lactobacillus acidophilus medium containing 3% (w/v) D-fructose. L. acidophilus was incubated at 37°C using MRS agar medium. Changes in pH values were measured for 48 hours. The non-sugar addition was also used as a comparison. Based on this research it could be seen that D-fructose slightly decreased pH in the medium at 48 hour incubation. This research might be useful to provide information on the potential use of D-fructose as a medium to maintain the reduction in pH.

Abstract The tautomer distributions of d ‑fructose, a popular model compound for biorefinery, in various lower alcohols and DMSO‑ d 6 (ROHs/DMSO‑ d 6) mixtures at 298 K were investigated by quantitative 13C NMR. The tautomer distributions of d ‑fructose in ethanol/DMSO‑ d 6 and methanol/DMSO‑ d 6 with different volume ratios of alcohols to DMSO‑ d 6 were also examined. For these normal alcohols (methanol, ethanol, n ‑propanol and n ‑butanol)/DMSO‑ d 6 , the tautomer distribution of d ‑fructose in methanol/DMSO‑ d 6 exhibited the shortest equilibration time (46 h) and the lowest concentration of β‑furanose (39.0%) at equilibrium. The fraction of fructofuranose (α‑furanose and β‑furanose) at equilibrium and time needed to reach equilibrium in branched chain alcohols/DMSO‑ d 6 obey the following order: 2‑propanol/DMSO‑ d 6 (62.2%, 320 h) > tert ‑butanol/DMSO‑ d 6 (61.6%, 307 h) > 2‑butanol/DMSO‑ d 6 (60.6%, 216 h) > isobutanol/DMSO‑ d 6 (57.8%, 134 h). For the diols/DMSO‑ d 6 , the time for the tautomer distribution of d ‑fructose to reach the equilibrium was found to be: 1,4‑butanediol/DMSO‑ d 6 (113 h) > 1,2‑propanediol/DMSO‑ d 6 (38 h) > ethylene glycol/DMSO‑ d 6 (36 h). For ethanol/DMSO‑ d 6 and methanol/DMSO‑ d 6 with respectively different volume ratios, the experimental results showed that the high concentration of ethanol or methanol increases the conversion rate of tautomers. Graphical abstract Unlabelled Image Highlights • Tautomer distributions of d ‑fructose in ROHs/DMSO‑ d 6 were investigated by 13C qNMR. • The effects of volumetric ratios between ethanol or methanol and DMSO‑ d 6 on tautomerization of d ‑fructose were examined. • Significant differences in the tautomer distributions of d ‑fructose in lower alcohols/DMSO‑ d 6 have been observed. • High concentration of ethanol or methanol increases the conversion rate of tautomers. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: The rare sugar D‐psicose has important physiological functions, and has been used as an ingredient in foods and dietary supplements. It can be mass produced from D‐fructose in industry. However, separation of D‐psicose from D‐fructose is difficult. RESULTS: In this research, a reaction purification system consisting of two continuous stirred tank reactors (CSTR) containing immobilized glucose isomerase (GI) and glucose oxidase (GOD), respectively, for D‐fructose removal was constructed. Using this system D‐fructose was transformed into gluconic acid and separated from D‐psicose easily using anion exchange resin. Modeling and simulation was carried out for this system and the model was verified by experiments and used in process predictions. CONCLUSION: D‐Psicose can be efficiently purified using the proposed reaction purification system. The final purity of the D‐psicose is 91.2%, which meets the need for crystallization to obtain highly purified product. The mathematical model developed for this system can simulate and predict the process well, which is useful in process analysis, prediction, and optimization to save time and costs compared with laboratory experiments. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Dental caries is an important global health concern and Streptococcus mutans has been established as a major cariogenic bacterial species. Reports indicate that a rare sugar, D-tagatose, is not easily catabolized by pathogenic bacteria. In the present study, the inhibitory effects of D-tagatose on the growth and biofilm formation of S. mutans GS-5 were examined. Monitoring S. mutans growth over a 24 h period revealed that D-tagatose prolonged the lag phase without interfering with the final cell yield. This growth retardation was also observed in the presence of 1% sucrose, although it was abolished by the addition of D-fructose. S. mutans biofilm formation was significantly inhibited by growth in sucrose media supplemented with 1 and 4% D-tagatose compared with that in a culture containing sucrose alone, while S. mutans formed granular biofilms in the presence of this rare sugar. The inhibitory effect of D-tagatose on S. mutans biofilm formation was significantly more evident than that of xylitol. Growth in sucrose media supplemented with D-tagatose significantly decreased the expression of glucosyltransferase, exo-ß-fructosidase and D-fructose-specific phosphotransferase genes but not the expression of fructosyltransferase compared with the culture containing sucrose only. The activity of cell-associated glucosyltransferase in S. mutans was inhibited by 4% D-tagatose. These results indicate that D-tagatose reduces water-insoluble glucan production from sucrose by inhibiting glucosyltransferase activities, which limits access to the free D-fructose released during this process and retards the growth of S. mutans. Therefore, foods and oral care products containing D-tagatose are anticipated to reduce the risk of caries by inhibiting S. mutans biofilm formation. [ABSTRACT FROM AUTHOR]

[Display omitted] • 5-Hydroxymethyl-2-furfurylamine (HMFA) was biosynthesized from biobased HMF. • The amination activity and thermostability of ω-transaminase mutant were improved. • Betaine:malonic acid − water medium was used as catalyst and solvent for producing HMF. • 900 mM HMF was aminated to HMFA in 97.4 % yield in betaine:malonic acid (5 wt%). • An efficient chemoenzymatic process gave a productivity of 0.43 g HMFA/g fructose. 5-Hydroxymethyl-2-furfurylamine (HMFA) is a key furan-based compound for manufacturing curing agents, additives, medicines and agrochemicals. It is also a good solvent for production of valuable biobased chemicals and biofuels. HMFA can be obtained by biological amination of 5-HMF by ω-transaminase (AT) from Aspergillus terreus. In this work, one stable triple mutant of AT ω-transaminase (HNILGD) was obtained via consensus mutagenesis. The half-life (t 1/2) of the mutant AT ω-transaminase [G292D (glycine to aspartate), H210N (histidine to asparagine) I77L (isoleucine to leucine)] was 1.43- and 2.14-fold higher than that of the wild-type AT ω-transaminase at 35 °C and 50 °C, respectively. Recombinant E. coli containing HNILGD ω-transaminase could aminate high load of 5-HMF (800 mM) to HMFA in the aqueous media [HMFA yield 92 %, selectivity 100 %]. In deep eutectic solvent betaine:malonic acid (5 wt%), HNILGD cells converted 900 mM 5-HMF to HMFA with a yield of 97.4 %. Moreover, d - fructose was chemoenzymatically transformed to HMFA in the betaine:malonic acid − water. 36.0 g/L of d - fructose was dehydrated into 5-HMF (63.9 % yield) with betaine:malonic acid (5 wt%) at 180 °C for 1 h, and the formed 5-HMF was further aminated to HMFA by HNILGD cells with amine donor d - alanine (d - Ala-to-5-HMF molar ratio 16:1) at 35 °C and pH 8.0 after 24 h in betaine:malonic acid (5 wt%), obtaining a productivity of 0.433 g HMFA per g d - fructose [cal. 0.96 g HMFA/(g d -fructose-derived 5-HMF)]. A significant enhancement of HMFA production from biobased d -fructose-derived HMF by a robust triple mutant ω-transaminase biocatalyst was successfully developed in a betaine:malonic acid − water system. [ABSTRACT FROM AUTHOR]

Glucose is transported in crustacean hepatopancreas and intestine by Na+-dependent co-transport, while Na+-dependent D-fructose influx has only been described for the hepatopancreas. It is still unclear if the two sugars are independently transported by two distinct cation-dependent co-transporter carrier systems. In this study, lobster (Homarus americanus) hepatopancreas brush border membrane vesicles (BBMV) were used to characterize, in detail, the cation-dependency of both D-[3H]-glucose and D-[3H]-fructose influxes, while in vitro perfused intestines were employed to determine the nature of cation-dependent sugar transport across this organ. Over the sodium concentration range of 0–100 mM, both [3H]-glucose and [3H]-fructose influxes (0.1 mM; 1 min uptakes) by hepatopancreatic BBMV were hyperbolic functions of [Na+]. [3H]-glucose and [3H]-fructose influxes by hepatopancreatic BBMV over a potassium concentration range of 15–100 mM were hyperbolic functions of [K+]. Both sugars displayed significant (p

D-allulose, a C-3 epimer of D-fructose, is a rare monosaccharide used as a food ingredient or a sweetener. In the present study, the in vitro metabolic stability of D-allulose was examined in biorelevant media, that is, simulated gastric fluid (SGF) and fasted state simulated intestinal fluid (FaSSIF) containing digestive enzymes, and in cryopreserved human and rat hepatocytes. The hepatocyte metabolic stabilities of D-allulose were also investigated and compared with those of fructose and erythritol (a sugar-alcohol with no calorific value). D-allulose was highly stable in SGF (97.8% remained after 60 min) and in FaSSIF (101.3% remained after 240 min), indicating it is neither pH-labile nor degraded in the gastrointestinal tract. D-allulose also exhibited high levels of stability in human and rat hepatocytes (94.5−96.8% remained after 240 min), whereas fructose was rapidly metabolized (43.1−52.6% remained), which suggested these two epimers are metabolized in completely different ways in the liver. The effects of D-allulose on glucose and fructose levels were negligible in hepatocytes. Erythritol was stable in human and rat hepatocytes (102.1−102.9% remained after 240 min). Intravenous pharmacokinetic studies in rats showed D-allulose was eliminated with a mean half-life of 72.2 min and a systemic clearance of 15.8 mL/min/kg. Taken together, our results indicate that D-allulose is not metabolized in the liver, and thus, unlikely to contribute to hepatic energy production.