Hexose Research Articles

Carbon isotope composition of birch syrup

Birch syrup is a forest product produced from tree sap using methods similar to those used in maple syrup production. This study presents the first measurements of the carbon isotope ratio of birch syrup, which is ultimately a function of tree physiology and environmental variables. Birch syrup has an average δ13C value = −25.31 ± 0.62‰ VPDB (1σ, n = 28), which is comparable to maple syrup. A few other tree syrups were analyzed for comparison: black walnut syrup has an average δ13C value = −25.52 ± 0.33‰ (n = 4) and one butternut syrup has a δ13C value = −23.88‰. All of these syrups are within the range of carbon isotope ratios typical of C3 plants, and are distinct from the carbon ratios of common C4 sugars derived from corn and sugarcane (δ13C value≈ −11 to −12‰). Detection of exogenous C4 sugars using carbon isotope ratio can be applied to birch syrup in the same way as it is used for other C3 foods such as maple syrup, honey, and fruit products.

Microwave assisted pretreatment of eucalyptus sawdust enhances enzymatic saccharification and maximizes fermentable sugar yield

Abstract There is an urgent need of sustainable and efficient methods for the production of biofuels and chemicals from lignocellulosic feedstock. The purpose of this study was to develop a mild, cost-effective and environmentally benign pretreatment for woody lignocellulose to maximize sugar yield via enzymatic saccharification. Microwave irradiation (MW) of Eucalyptus regnans sawdust in water was investigated and compared directly against conventional liquid hot water (LHW) pretreatment. Following 30 min microwave irradiation at 180 °C, the sugar yield was 3.5 times higher using MW than LHW pretreatment under the same conditions. Complete release of C5 and C6 sugars was achieved after the two-step method of MW pretreatment followed by enzymatic hydrolysis, compared with only 4% without pretreatment and 31% after LHW. Removal of ‘lignin droplets’ formed on the surface of the pretreated fibers via flowing hot water showed only minor improvement in the yield of enzymatic saccharification. Our results support the hypothesis that lignin prevents access of enzymes rather than inhibits their activity. MW accelerated depolymerization of hemicellulose, opening the structure more than LHW pretreatment.

Branching-First: Synthesizing C–C Skeletal Branched Biobased Chemicals from Sugars

A novel strategy to biobased chemicals with a branched carbon skeleton is introduced. Hereto, small sugars, such as 1,3-dihydroxyacetone, are coupled catalytically to obtain branched C6 sugars, such as dendroketose, in high yield at mild conditions. By bringing this branching step up front, at the level of the sugar feedstock (branching-first), new opportunities for the synthesis of useful chemicals arise. Here, we show that the branched sugar can be efficiently valorized into (i) new branched polyols and (ii) short branched alkanes. The first route preserves most of the original sugar functionality by hydrogenation with Ru/C and renders access to branched polyols with three primary alcohol groups. These molecules are potentially interesting as plasticizers, cross-linkers, or detergent precursors. The second valorization route demonstrates a facile hydrodeoxygenation of the branched sugars toward their corresponding branched alkanes (e.g., 2-methylpentane). The highest alkanes yields (>65 mol % C) are obt...

Evaluation of a combined lignocellulosic / waste water bio‐refinery for the simultaneous production of valuable biochemical products and the remediation of acid mine drainage

AbstractThe additional costs required for the pre‐treatment of lignocellulosic bio‐mass prior to enzymatic hydrolysis have limited the commercial implementation of lignocellulosic bio‐chemical production. The use of acidic mine drainage (AMD) water as an acid source for lignocellulosic pre‐treatment has recently been investigated. Large quantities of AMD in South Africa suggest that AMD can be obtained cheaply, thus reducing the cost and increasing the potential of lignocellulosic bio‐chemicals. Acidic mine drainage could undergo further remediation using sulfate‐reducing bacteria (SRB) so that the water is suitable for release. The feasibility of such a system could be greatly improved if this process were to be incorporated within a bio‐refinery, such that all fractions of the bio‐mass are used to produce multiple products. This paper investigates such a bio‐refinery system, and evaluates the different options based on the bio‐refinery complexity profile (BCP). Due to the abundance of grass in the regions where AMD is generated, this was found to be the most suitable feedstock. The most feasible bio‐refinery option was found to produce ethanol through fermentation of C6 sugars, although it is recommended that further investigation be conducted into additional high‐value bio‐chemicals from the C6 sugar platform. C5 sugars released in pre‐treatment could be used as a substrate by SRB for AMD remediation. Gasification and direct combustion of lignin had similar BCPs and thus further investigation is required to determine the preferred path. Similarly, further investigation is required for the best processing route for distillery silage. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Catalytic conversion of hemicellulosic sugars derived from biomass to levulinic acid

Catalytic conversion of hemicellulosic sugars from biomass towards levulinic acid production was conducted using modified-zeolite Y (commercial). The zeolite was treated by NaOH of different concentration (x M) before used for the conversion of C5 sugars to levulinic acid. The modified zeolites had a larger porosity and an increased concentration of stronger acid sites compared to the untreated zeolite. Levulinic acid yield of 4.6% (conversion of C5 sugar to levulinic acid: 42.7%) was maximized at 190 °C and reaction time of 180 min (batch reactor), when using the zeolite treated with 0.25 M NaOH. In addition, with the absence of C6 sugar, the conversion of C5 sugar was higher than that of C5-C6 sugar mixture. The present work provides a new heterogeneous catalytic approach for levulinic acid production from liquid hydrolysates (by-product of biomass utilization).

Microwave-Assisted Oxalic Acid Pretreatment for the Enhancing of Enzyme Hydrolysis in the Production of Xylose and Arabinose from Bagasse.

In this study, highly-efficient hydrolysis of bagasse into xylose and arabinose sugars (C5 sugars) was developed by microwave-assisted oxalic acid pretreatment under mild reaction conditions. The effects of acid and hydrolysis conditions on the C5 sugar yields were discussed. The results showed that oxalic acid performed better than hydrochloric acid and maleic acid, and was a promising alternative to sulfuric acid for xylose production at the same acid concentration. The maximum yields of xylose (95.7%) and arabinose (91.5%) were achieved via the microwave-assisted oxalic acid pretreatment (120 °C, 10 min, 0.4 mol/L, solid–liquid ratio of 1:50 g/mL), indicating that almost all xylan-type hemicelluloses were released from the cell wall and hydrolyzed into C5 sugars. After pretreatment, more than 90% of the cellulose in the residual bagasse was converted to glucose (92.2%) by enzymatic hydrolysis. This approach could realize the highly-efficient hydrolysis of xylan from bagasse into C5 sugars, which would enhance the enzyme hydrolysis of treated bagasse into glucose.

Lignocellulosic Biomass Pretreatment for Biorefinery: A Review

Lignocellulosic biomass consists of cellulose, hemicellulose, and lignin, which have the potential to produce the so-called green chemicals. Many processes are available at different scales (e.g. labs, pilots, demos, commercials), utilizing lignocellulosic biomass as the raw material. Due to its complicated chemical structures, lignocellulosic biomass must be pretreated before it can be processed further. Simultaneous separation of cellulose, hemicellulose, and lignin from the biomass is an important step to maximize the full potential of the biomass. In this review, several well-known biomass pretreatment technologies are evaluated. These are low pH process (e.g. dilute acid, steam explosion, hot water liquid, and concentrated acid), high pH (e.g. NaOH, lime, NH3), organosolv, ozonolysis, CO2 explosion, and ionic liquids. The objective of this review is to understand how effective the pretreatment process for separating cellulose, hemicellulose, and lignin. Based on this review, organosolv is the only pretreatment process that is capable of separating cellulose, C5 sugars (from hemicellulose), and lignin, simultaneously. This process is currently at pilot scales of 30 – 100 ton per day of biomass feedstock.

Simultaneous Catalytic Conversion of C6 and C5 Sugars to Methyl Lactate in Near-critical Methanol with Metal Chlorides

Cellulose and hemicellulose make up roughly two-thirds of lignocellulose. Currently, research is mainly focused on converting them to different chemicals, which causes low utilization rates and high separation costs. In this work, the simultaneous conversion of C6 and C5 sugars from cellulose and hemicellulose to methyl lactate in near-critical methanol with 15 different types of metal chlorides was studied. The trends of the catalytic conversions of C6 and C5 sugars with different metal chlorides were similar. Methyl lactate yield initially increased and then decreased steadily with an increase in the pKa value of the metal ions, which suggested that medium Lewis acidity was favorable for the production of methyl lactate. A possible reaction mechanism was proposed. The results will provide direction for the preparation of heterogeneous catalysts for simultaneously converting cellulose and hemicellulose to methyl lactate.

Production of 1,3‐butadiene and ε‐caprolactam from C6 sugars: Techno‐economic analysis

AbstractThis study assesses the techno‐economic performance of production lines for obtaining 1,3‐butadiene and ε‐caprolactam from C6 sugars. Process models were developed to assess their technical performance and to derive inputs for economic analysis. The economic assessment was carried out using net present value (NPV) and production costs as indicators. Sensitivity analyses were carried out to account for the effects of variations in inputs, such as processing capacity, valorization of humins, and prices, on the economic outputs. Results indicate that both production lines perform similarly from an energy intensity point of view (34–50 MJ/kg of main product). However, in terms of yield (kg of product per kg C6 sugar), caprolactam shows higher values by a factor of 1.6–3.6 in comparison to that of butadiene. The butadiene production line is not economically attractive, showing a negative NPV (−647 to −642 M€) and production costs 3–5 times higher than the reference market price (Case I 4369 €/tonne, Case II 3406 €/tonne). The caprolactam production line seems to be unfeasible with negative NPV (−229 M€) and production costs 30% higher than the reference price (Case III 2595 €/tonne, Case IV 1875 €/tonne). However, if the production yield is increased, the caprolactam production line becomes economically attractive with production costs 6% lower than its reference market price. The production costs of caprolactam can be further decreased if the process capacity is increased, reflecting the benefits of the economies of scale, as well as including heat and power produced from humins. Overall, the caprolactam production line shows higher economic potential. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Exploration and optimization of mixed acid synergistic catalysis pretreatment for maximum C5 sugars

The liquid hot water (LHW) pretreatment could be strengthened by acetic and lactic acids produced from the process. The synergistic effect of the mixed acid catalyst of lactic acid and acetic acid was investigated for the purpose of maximization of the overall C5 sugars yield. Individual acids (acetic and lactic acid) and mixed acid were used to strengthen the LHW pretreatment at different conditions. The results showed that the suitable conditions of mixed acid synergistic catalysis was at 180 °C for 60 min and 3 wt% mixed acid where the ratio of 40% (i.e. 0.40 in mass fraction of lactic acid in mixed acid). Response surface methodology (RSM) was applied to further optimize this process. The highest yield of C5 sugars of 93.83% according to theoretical predicted model, was close to the experiment value of 92.53% at 177 °C for 67 min and with the ratio of mixed acid of 40%.

Oxidation of Aldoses Contained in Softwood Hemicellulose Acid Hydrolysates into Aldaric Acids under Alkaline or Noncontrolled pH Conditions

The hemicellulose-derived aqueous solution of C6 and C5 sugars (d-mannose, d-galactose, d-glucose, d-xylose, l-arabinose), obtained from the extraction and hydrolysis of the hemicellulosic polymers in softwoods prior to the production of pulp, was catalytically converted to the corresponding aldaric acids under alkaline (Pt/C) or native (Au–Pt/ZrO2) aqueous conditions with air. The inhibiting effect of some residual impurities and degraded compounds in the hydrolysate was confirmed, such as colored unsaturated compounds and 5-hydroxymethylfurfural. A combined purification process consisting of filtration, demineralization by ion-exchange resins, evaporation, and active carbon treatment of the raw aqueous-stream gave a purified hydrolysate of aldoses that was oxidized to hexaric and pentaric acids. The yields were close to those of a synthetic solution of the pure sugars with the same distribution. The yields of aldaric acids accounted for ca. 50% of hexaric acids and up to 70% of pentaric acids.

Dual acidic titania carbocatalyst for cascade reaction of sugar to etherified fuel additives

An inexpensive carbocatalyst containing Brønsted acidic sulfonic acid group and Lewis acidic Ti4+ is found to be effective for cascade conversion of C6 sugar to 5-ethoxymethylfurfural (EMF) via sequential dehydration, and etherification reactions. HMF and fructose conversions at mild conditions achieved 91% and 64% EMF yields, respectively. The results indicate that the two acid sites interplay synergistically for high EMF yield and minimal ring-opened product ethyl levulinate (EL), another promising biofuel additive. Etherification of 2,5-bis(hydroxymethyl)furan (BHMF) with alcohols of varying carbon lengths formed alkoxymethylfurans (AMF) with high yields. The catalyst retained good activity upon recycling. The nature and strength of the acid sites are elucidated.

Determination of the physicochemical properties and 13C/12C isotope ratios of some honeys from the northeast Anatolia region of Turkey

In the study, the honey was subjected to analyses after being taken from different producers immediately after the end of the production season. 13C/12C analysis was performed on the samples using an isotope ratio mass spectrometer (EA-IRMS) combined with an elemental analyzer. In all of the honey samples, the δ13C value was found to be more negative than −23.5‰ and even the C4 sugar ratio was found to be lower than 7%. The results from the physicochemical analysis of the samples were determined to be 15.9 ± 1.6% for the moisture content, 82.8 ± 1.1 for brix, 0.183 ± 0.02 mS/cm for conductivity, 24.4 ± 4.0 meq/kg for total acidity, 546 ± 80 mg/kg for proline, and 14.5 ± 3.5 for diastase activity. In addition, the sugar content was determined to be 38.8 ± 1.8% for fructose, 30.2 ± 1.7% for glucose, 69.1 ± 3.3% for fructose + glucose, and 1.29 ± 0.5 for fructose/glucose. When the analysis results were evaluated according to the relevant standards and codex, it was evident that the honey samples produced within the region are of very good quality.

Engineering Escherichia coli to grow constitutively on D-xylose using the carbon-efficient Weimberg pathway.

Bio-production of fuels and chemicals from lignocellulosic C5 sugars usually requires the use of the pentose phosphate pathway (PPP) to produce pyruvate. Unfortunately, the oxidation of pyruvate to acetyl-coenzyme A results in the loss of 33 % of the carbon as CO2, to the detriment of sustainability and process economics. To improve atom efficiency, we engineered Escherichia coli to utilize d-xylose constitutively using the Weimberg pathway, to allow direct production of 2-oxoglutarate without CO2 loss. After confirming enzyme expression in vitro, the pathway expression was optimized in vivo using a combinatorial approach, by screening a range of constitutive promoters whilst systematically varying the gene order. A PPP-deficient (ΔxylAB), 2-oxoglutarate auxotroph (Δicd) was used as the host strain, so that growth on d-xylose depended on the expression of the Weimberg pathway, and variants expressing Caulobacter crescentus xylXAB could be selected on minimal agar plates. The strains were isolated and high-throughput measurement of the growth rates on d-xylose was used to identify the fastest growing variant. This strain contained the pL promoter, with C. crescentus xylA at the first position in the synthetic operon, and grew at 42 % of the rate on d-xylose compared to wild-type E. coli using the PPP. Remarkably, the biomass yield was improved by 53.5 % compared with the wild-type upon restoration of icd activity. Therefore, the strain grows efficiently and constitutively on d-xylose, and offers great potential for use as a new host strain to engineer carbon-efficient production of fuels and chemicals via the Weimberg pathway.

Nitrogen and phosphorus supply controls soil organic carbon mineralization in tropical topsoil and subsoil

Nitrogen (N) deposition to soils is globally rising, but its effect on soil organic carbon (SOC) turnover is still uncertain. Moreover, common theories of stoichiometric decomposition and microbial N mining predict opposing effects of N supply on SOC turnover. We hypothesized that the effect of N deposition on SOC turnover depends on initial soil nutrient conditions. Thus, we sampled tropical forests and rubber gardens with pronounced gradients of nutrient availability from the topsoil to the deep subsoil (up to 400 cm) and measured substrate-induced respiration (SIR) for 30 days in four treatments (C, CN, CP, CNP additions). A natural 13C abundance approach was conducted to quantify priming effects (PE) of the added C on SOC mineralization. For this purpose we assessed the 13CO2 isotope composition after adding a C4 sugar to the C3 soil; to correct for isotopic fractionation a treatment with C3 sugar additions served as control. We found that nutrient additions to topsoil did neither alter cumulative CO2 release within 30 days (SIRacc) nor PE (PE = 1.6, i.e., sugar additions raised the release of SOC-derived CO2 by a factor of 1.6). In the upper subsoil (30–100 cm), however, both CN and CP additions increased SIRacc (by 239% and 92%, respectively) and the PE (PE = 5.2 and 3.3, respectively) relative to the treatments that received C only (PE = 1.7), while CNP additions revealed the largest increase of SIRacc (267%) and PE (PE = 6.0). In the deep subsoil (>130 cm depth), only the CNP addition consistently increased SIRacc (by 871%) and PE (PE = 5.2) relative to only C additions (PE = 2.0). We conclude that microbial activity was not limited by nutrients in the topsoil but was co-limited by both N and P in the subsoil. The results imply that microbes mine nutrients from previously unavailable pools under the conditions that 1) deficiency actually exists, 2) co-limitation is alleviated, and 3) nutrient reserves are present. Yet, as opposed to microbial nutrient mining theories, we showed that the subsoil PE is highest when nutrient supply matches microbial demand. As a result also N deposition might exert variable effects on SOC turnover in tropical soils: it might have no effect in nutrient-rich topsoils and in co-limited subsoils without P reserves but might increase SOC turnover in co-limited subsoils with potentially acquirable P reserves.

Effect of Lewis and Brønsted acidity on glucose conversion to 5-HMF and lactic acid in aqueous and organic media

Among the different metal-promoted catalysts for the conversion of C6 sugars to platform chemicals, Sn-based catalysts have demonstrated high activity for different types of reactions, such as isomerization, retro-aldol conversion and dehydration of glucose or its isomers. The form of Sn species, as oxides or ions, along with the properties of the support are important factors determining the prevalent reaction pathway and product distribution. In this framework, we have studied the conversion of glucose mainly in biphasic (H2O/DMSO) media, using four types of Sn-based catalysts, i.e. Sn(II) and Sn(IV) as homogeneous catalysts (Cl- salts) or as the respective oxides in heterogeneous systems, Sn(IV) as SnO2 supported on γ-Al2O3, zeolites (ZSM-5 and Beta) or mesoporous aluminosilicates (Al-MCM-41), and Snδ+ as ion-exchange cations on the above zeolites. The solid catalysts were characterized by XRD, FT-IR/pyridine, ICP-OES, XRF and N2 porosimetry. Under the studied conditions, the main products obtained were 5-HMF and lactic acid in both the homogeneous and heterogeneous systems. Based on the results obtained, it was concluded that the Lewis acidity offered by Sn oxides promotes the retro-aldol reaction pathway towards lactic acid, while the Lewis acidity offered by γ-Al2O3 enhances the synthesis of both 5-HMF and lactic acid. By combining these two functions, the Sn impregnated γ-Al2O3 catalysts induce further increase of both 5-HMF and lactic acid yields. In case of catalysts that possess Brønsted acidity as well (i.e. Sn ion-exchanged or impregnated zeolites and Al-MCM-41), dehydration reactions are promoted and the product selectivity is shifted towards 5-HMF synthesis. The highest 5-HMF molar yield of 27.5% (at complete glucose conversion) was achieved by Sn20/γ-Al2O3 accompanied by lactic acid at 16.5% molar yield. For this catalyst the effect of the solvent, catalyst concentration and reaction temperature and time, were further evaluated.

Engineering E. coli for simultaneous glucose\u2013xylose utilization during methyl ketone production

BackgroundWe previously developed an E. coli strain that overproduces medium-chain methyl ketones for potential use as diesel fuel blending agents or as flavors and fragrances. To date, the strain’s performance has been optimized during growth with glucose. However, lignocellulosic biomass hydrolysates also contain a substantial portion of hemicellulose-derived xylose, which is typically the second most abundant sugar after glucose. Commercialization of the methyl ketone-producing technology would benefit from the increased efficiency resulting from simultaneous, rather than the native sequential (diauxic), utilization of glucose and xylose.ResultsIn this study, genetic manipulations were performed to alleviate carbon catabolite repression in our most efficient methyl ketone-producing strain. A strain engineered for constitutive expression of xylF and xylA (involved in xylose transport and metabolism) showed synchronized glucose and xylose consumption rates. However, this newly acquired capability came at the expense of methyl ketone titer, which decreased fivefold. Further efforts were made to improve methyl ketone production in this strain, and we found that two strategies were effective at enhancing methyl ketone titer: (1) chromosomal deletion of pgi (glucose-6-phosphate isomerase) to increase intracellular NADPH supply and (2) downregulation of CRP (cAMP receptor protein) expression by replacement of the native RBS with an RBS chosen based upon mutant library screening results. Combining these strategies resulted in the most favorable overall phenotypes for simultaneous glucose–xylose consumption without compromising methyl ketone titer at both 1 and 2% total sugar concentrations in shake flasks.ConclusionsThis work demonstrated a strategy for engineering simultaneous utilization of C6 and C5 sugars in E. coli without sacrificing production of fatty acid-derived compounds.

Gene stacking of multiple traits for high yield of fermentable sugars in plant biomass

BackgroundSecond-generation biofuels produced from biomass can help to decrease dependency on fossil fuels, bringing about many economic and environmental benefits. To make biomass more suitable for biorefinery use, we need a better understanding of plant cell wall biosynthesis. Increasing the ratio of C6 to C5 sugars in the cell wall and decreasing the lignin content are two important targets in engineering of plants that are more suitable for downstream processing for second-generation biofuel production.ResultsWe have studied the basic mechanisms of cell wall biosynthesis and identified genes involved in biosynthesis of pectic galactan, including the GALS1 galactan synthase and the UDP-galactose/UDP-rhamnose transporter URGT1. We have engineered plants with a more suitable biomass composition by applying these findings, in conjunction with synthetic biology and gene stacking tools. Plants were engineered to have up to fourfold more pectic galactan in stems by overexpressing GALS1, URGT1, and UGE2, a UDP-glucose epimerase. Furthermore, the increased galactan trait was engineered into plants that were already engineered to have low xylan content by restricting xylan biosynthesis to vessels where this polysaccharide is essential. Finally, the high galactan and low xylan traits were stacked with the low lignin trait obtained by expressing the QsuB gene encoding dehydroshikimate dehydratase in lignifying cells.ConclusionThe results show that approaches to increasing C6 sugar content, decreasing xylan, and reducing lignin content can be combined in an additive manner. Thus, the engineered lines obtained by this trait-stacking approach have substantially improved properties from the perspective of biofuel production, and they do not show any obvious negative growth effects. The approach used in this study can be readily transferred to bioenergy crop plants.

Investigating the strategies for microbial production of trehalose from lignocellulosic sugars.

Trehalose, a multi-functional and value-added disaccharide, can be efficiently biosynthesized from glucose by using a synergetic carbon utilization mechanism (SynCar) which coupled phosphoenolpyruvate (PEP) generation from the second carbon source with PEP-dependent phosphotransferase system (PTS) to promote non-catabolic use of glucose. Considering glucose and xylose present in large amounts in lignocellulosic sugars, we explored new strategies for conversion of both sugars into trehalose. Herein, we first attempted trehalose production from xylose directly, based on which, synergetic utilization of glucose, and xylose prompted by SynCar was implemented in engineered Escherichia coli. As the results, the final titer of trehalose reached 5.55 g/L in shake flask experiments. The conversion ratio or utilization efficiency of glucose or xylose to trehalose was around fourfold higher than that of the original strain (YW-3). This work not only demonstrated the possibility of directly converting xylose (C5 sugar) into trehalose (C12 disaccharide), but also suggested a promising strategy for trehalose production from lignocellulosic sugars for the first time.

Direct conversion of C6 sugars to methyl glycerate and glycolate in methanol.

The present work deals with the one-pot conversion of C6 sugars to methyl glycerate and glycolate via a cascade of retro-aldol condensation and oxidation processes catalyzed by using MoO3 as the Lewis acid catalyst and Au/TiO2 as the oxidation catalyst in methanol. Methyl glycerate (MGLY) is the product of C6 ketose (fructose), while methyl glycolate (MG) is produced from C6 aldose (mannose, glucose). It is found that a good one-pot match between two reactive processes is the key to the production of MGLY and MG with high yield (27.6% MGLY and 39.2% MG). A separated retro-aldol condensation and oxidation process greatly decreases their yields, and even no MGLY can be obtained in this separated process. We attribute this to high instability of glyceraldehyde/glycolaldehyde and their different reaction pathways which mainly depend on whether acetalization of retro-aldol products (glyceraldehyde and glycolaldehyde) occurs with methanol or not. This result opens a new prospect on the accumulation of C3 products other than lactate from biomass-derived carbohydrates.