Production Of Aromatic Compounds Research Articles

Heterogeneous Diels–Alder catalysis for biomass-derived aromatic compounds

This review highlights Diels–Alder heterogeneous catalysis for the production of biomass-derived aromatic compounds.

Biotechnological production of aromatic compounds of the extended shikimate pathway from renewable biomass

Aromatic chemicals that contain an unsaturated ring with alternating double and single bonds find numerous applications in a wide range of industries, e.g. paper and dye manufacture, as fuel additives, electrical insulation, resins, pharmaceuticals, agrochemicals, in food, feed and cosmetics. Their chemical production is based on petroleum (BTX; benzene, toluene, and xylene), but they can also be obtained from plants by extraction. Due to petroleum depletion, health compliance, or environmental issues such as global warming, the biotechnological production of aromatics from renewable biomass came more and more into focus. Lignin, a complex polymeric aromatic molecule itself, is a natural source of aromatic compounds. Many microorganisms are able to catabolize a plethora of aromatic compounds and interception of these pathways may lead to the biotechnological production of value-added aromatic compounds which will be discussed for Corynebacterium glutamicum. Biosynthesis of aromatic amino acids not only gives rise to l-tryptophan, L-tyrosine and l-phenylalanine, but also to aromatic intermediates such as dehydroshikimate or chorismate from which value-added aromatic compounds can be derived. In this review, we will summarize recent strategies for the biotechnological production of aromatic and related compounds from renewable biomass by Escherichia coli, Pseudomonas putida, C. glutamicum and Saccharomyces cerevisiae. In particular, we will focus on metabolic engineering of the extended shikimate pathway.

Yeast factories for the production of aromatic compounds: from building blocks to plant secondary metabolites.

The aromatic amino acid biosynthesis pathway is a source to a plethora of commercially relevant chemicals with very diverse industrial applications. Tremendous efforts in microbial engineering have led to the production of compounds ranging from small aromatic molecular building blocks all the way to intricate plant secondary metabolites. Particularly, the yeast Saccharomyces cerevisiae has been a great model organism given its superior capability to heterologously express long metabolic pathways, especially the ones containing cytochrome P450 enzymes. This review contains a collection of state-of-the-art metabolic engineering work devoted towards unraveling the mechanisms for enhancing the flux of carbon into the aromatic pathway. Some of the molecules discussed include the polymer precursor muconic acid, as well as important nutraceuticals (flavonoids and stilbenoids), and opium-derived drugs (benzylisoquinoline alkaloids).

Complete Genome Sequence of Staphylococcus carnosus LTH 3730.

Specific strains of the apathogenic coagulase-negative species Staphylococcus carnosus are frequently used as meat starter cultures, as they contribute to color formation and the production of aroma compounds. Here, we report the complete genome sequence of S. carnosus LTH 3730, a strain isolated from a fermented fish product.

Photocatalytic Oxidation of Lignin Model Systems by Merging Visible-Light Photoredox and Palladium Catalysis.

Lignin valorization has long been recognized as a sustainable solution for the renewable production of aromatic compounds. Two-step oxidation/reduction strategies, whereby the first oxidation step is required to "activate" lignin systems for controlled fragmentation reactions, have recently emerged as viable routes toward this goal. Herein we describe a catalytic protocol for oxidation of lignin model systems by combining photoredox and Pd catalysis. The developed dual catalytic protocol allowed the efficient oxidation of lignin model substrates at room temperature to afford the oxidized products in good to excellent yields.

In Depth Proteome Analysis of Ripening Muscadine Grape Berry cv. Carlos Reveals Proteins Associated with Flavor and Aroma Compounds.

Ripening in nonclimacteric fruits such as grape involves complex chemical changes that have a profound influence on the accumulation of flavor and aroma compounds distinct to a particular grape genotype. In this study, proteome characterization of wine type bronze muscadine grape (Vitis rotundifolia cv. Carlos), primarily grown in the Southeastern United States was performed during berry ripening. Stage-specific protein expression was obtained among different stages of berries. Differential analysis showed the expression of 522 proteins that regulate diverse biological processes and metabolic pathways. Of these, 30 proteins are associated with the production of key phenolic compounds, whereas 25 are associated with the production of muscadine aroma compounds. These proteins are involved in the phenylpropanoid pathway, terpene synthesis, fatty acid derived volatiles and esters that affect muscadine berry flavor and aroma characteristics. Further, gene expression analysis during ripening validated the expression pattern of 12 proteins. Catechin, epicatechin, and four stilbenes were quantified to correlate observed proteome changes. This study not only revealed biochemical changes during muscadine berry ripening but also offers indicators for marker-assisted breeding to enhance organoleptic properties of muscadine grape to improve its flavor and aroma properties.

Evaluation of the co-pyrolysis of lignin with plastic polymers by TG-FTIR and Py-GC/MS

Lignin extracted from black liquor was co-pyrolyzed with three kinds of plastic polymers (low density polyethylene (LDPE); polycarbonate (PC); polystyrene (PS)), in order to investigate the effect of plastic polymers on the distribution of pyrolysis products (especially monomeric aromatic compounds). TG-FTIR and Py-GC/MS were employed to understand the thermal behavior and identify the typical products from the pyrolysis of individual samples and their mixtures (mass ratio for the mixture: 1:1). For TG-FTIR analysis, the thermal decomposition behavior of lignin-PC mixture exhibits notable difference between the experimental and estimated results over that of lignin-PS mixture and lignin-LDPE mixture. The apparent activation energy for the main conversion zone of co-pyrolysis of lignin with PC (73.08 kJ/mol) is lowest among those of the lignin-plastic mixtures (180.17 kJ/mol for lignin with LDPE and 179.91 kJ/mol for lignin with PS mixtures), suggesting the strongest interaction between lignin and PC. The H2O produced by the decomposition of lignin at low temperature may promote the hydrolytic reaction of PC and the release of CO2. The production of several aromatic compounds assigned to lignin pyrolysis was suppressed by the addition of PC or LDPE, while the formation of monomer aromatic hydrocarbons was notably promoted during the co-pyrolysis of lignin with PS.

Investigating strain dependency in the production of aromatic compounds in Saccharomyces cerevisiae.

Although Saccharomyces cerevisiae is the most highly domesticated yeast, strain dependency in biotechnological processes still remains as a common, yet poorly understood phenomenon. To investigate this, the entrance to the aromatic amino acid biosynthetic pathway was compared in four commonly used S. cerevisiae laboratory strains. The strains were engineered to accumulate shikimate by overexpressing a mutant version of the pentafunctional ARO1 enzyme with disrupted activity in the shikimate kinase subunit. Carbon tracing and 13 C metabolic flux analysis combined with quantitative PCR, revealed that precursor availability and shikimate production were dramatically different in the four equally engineered strains, which were found to be correlated with the strains' capacity to deal with protein overexpression burden. By implementing a strain-dependent approach, the genetic platform was reformulated, leading to an increase in yield and titer in all strains. The highest producing strain, INVSc1-SA3, produced 358 mg L-1 of shikimate with a yield of 17.9 mg g-1glucose. These results underline the importance of strain selection in developing biological manufacturing processes, demonstrate the first case of high production of shikimate in yeast, and provide an appropriate platform for strain selection for future production of aromatic compounds. Biotechnol. Bioeng. 2016;113: 2676-2685. © 2016 Wiley Periodicals, Inc.

The effects of reactants ratios, reaction temperatures and times on Maillard reaction products of the L-ascorbic acid/L-glutamic acid system

The transformation law of the Maillard reaction products with three different reactants ratios - equimolar reactants, excess L-glutamic acid and excess L-ascorbic acid reaction respectively, five different temperatures, and different time conditions for the L-ascorbic acid / L-glutamic acid system were investigated. Results showed that, the increase of the reaction time and temperature led to the increase of the browning products, uncoloured intermediate products, as well as aroma compounds. Compared with the equimolar reaction system, the excess L-ascorbic acid reaction system produced more browning products and uncoloured intermediate products, while the aroma compounds production remained the same. In the excess L-glutamic acid system, the uncoloured intermediate products increased slightly, the browning products remained the same, while the aroma compounds increased.

Target Analysis of Polycyclic Aromatic Hydrocarbons (PAHs) in Consumer Products and Total Content of Polycyclic Aromatic Compounds (PACs)

ABSTRACTThe fabrication of consumer products is tightly linked to the usage of polymeric materials. The application of mineral oil products as plasticizers or lubricants in this manufacture is very common and so is the addition of carbon black for coloring and abrasion resistance purposes. Whereas mineral oils often contain highly alkylated aromatic species, alkylation of polycyclic aromatic compounds (PACs) is rather low or even absent in the case of carbon black. Since they are broadly applied in various products, consumers might get exposed to PACs, for instance, via dermal contacts. Here, we characterized several commodities not only via the common way of targeted analysis for their contents on PAHs, but also with regard to its total amounts of unsubstituted and substituted aromatic hydrocarbons. The methods applied to analyze consumer products were as follows: (i) online coupling of liquid chromatography to gas chromatography with flame ionization detection (LC-GC-FID) for quantification of total PAH and mineral oil saturated hydrocarbon (MOSH) contents; (ii) coupling of tandem mass spectrometry to gas chromatography (GC-MS/MS) to quantify occasionally occurring PAHs with high specificity; and (iii) 2D gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-MS) to characterize the complex mixtures concerning analytes’ ring systems and degrees of alkylation. We found PAH contents in the range of parts per million (ppm) in consumer products, while overall amounts of aromatics were in the percent range.

Construction of a Corynebacterium glutamicum platform strain for the production of stilbenes and (2S)-flavanones

Corynebacterium glutamicum is an important organism in industrial biotechnology for the microbial production of bulk chemicals, in particular amino acids. However, until now activity of a complex catabolic network for the degradation of aromatic compounds averted application of C. glutamicum as production host for aromatic compounds of pharmaceutical or biotechnological interest. In the course of the construction of a suitable C. glutamicum platform strain for plant polyphenol production, four gene clusters comprising 21 genes involved in the catabolism of aromatic compounds were deleted. Expression of plant-derived and codon-optimized genes coding for a chalcone synthase (CHS) and a chalcone isomerase (CHI) in this strain background enabled formation of 35mg/L naringenin and 37mg/L eriodictyol from the supplemented phenylpropanoids p-coumaric acid and caffeic acid, respectively. Furthermore, expression of genes coding for a 4-coumarate: CoA-ligase (4CL) and a stilbene synthase (STS) led to the production of the stilbenes pinosylvin, resveratrol and piceatannol starting from supplemented phenylpropanoids cinnamic acid, p-coumaric acid and caffeic acid, respectively. Stilbene concentrations of up to 158mg/L could be achieved. Additional engineering of the amino acid metabolism for an optimal connection to the synthetic plant polyphenol pathways enabled resveratrol production directly from glucose. The construction of these C. glutamicum platform strains for the synthesis of plant polyphenols opens the door towards the microbial production of high-value aromatic compounds from cheap carbon sources with this microorganism.

A Dual Catalyst with SERS Activity for Probing Stepwise Reduction and Oxidation Reactions

AbstractAromatic azo compounds are high‐value chemicals extensively used as pigments, drugs, and food additives, but their production typically requires stoichiometric amounts of environmentally unfriendly metals or nitrites. There is an urgent need to develop a dual catalytic system capable of reducing nitroaromatics to aromatic amines, followed by their oxidation to azo compounds. Here we report such a dual catalyst based on Ag@Pd‐Ag core‐frame nanocubes for the stepwise conversion of 4‐nitrothiophenol to trans‐4,4′‐dimercaptoazobenzene under ambient conditions. Our in situ surface‐enhanced Raman spectroscopy study reveals three sequential processes that include the Pd‐catalyzed reduction of 4‐nitrothiophenol to 4‐aminothiophenol by hydrogen, a period during which the 4‐aminothiophenol remain unchanged until all hydrogen has depleted, and the Ag‐catalyzed oxidation of 4‐aminothiophenol to trans‐4,4′‐dimercaptoazobenzene by the O2 from air. This work will lead to an environmentally friendly and sustainable approach to the production of aromatic azo compounds.

Integrated Dual-Production Mode Modeling and Multiobjective Optimization of an Industrial Continuous Catalytic Naphtha Reforming Process

Catalytic naphtha reforming is a key process both in refineries and in the production of aromatic compounds. However, the characteristics of dual-production modes render the process model difficult to adapt to changing production needs. Because catalytic naphtha reforming has a complicated reaction mechanism along with multiple operation variables and objectives, its optimization is challenging. We herein report the modeling and optimization steps employed to resolve these issues. A detailed continuous catalytic regenerative (CCR) reforming process model was established, integrating the reaction kinetic model, reactor model, heater model, compressor model, and separator model. On the basis of the CCR model, multiobjective optimizations were performed, and a hierarchical structure of stochastic algorithm was proposed, thus reducing computation costs during model calculations. Three multiobjective optimization problems were solved using the proposed algorithm, with these cases being based on refinery produc...

Fast co-pyrolysis of low density polyethylene and biomass residue for oil production

Co-pyrolysis of low density polyethylene (LDPE) with three kinds of biomass was performed in a dropdown tube reactor. The synergistic effect was investigated by comparing the experimental relative yield and characteristics of oil with the calculated ones based on the results from the pyrolysis of the individual components in the mixture. It is found that the maximum oil relative yield in the case of co-pyrolysis process was obtained at 600°C, which was significantly higher than the optimum temperature of biomass or LDPE pyrolysized alone. Although the inorganic elements in biomass improved the decomposition of LDPE, more organics with larger molecule weight (>C12) were produced due to the further reaction between the decomposition products from LDPE and biomass. The synergistic effect was positive for the production of aliphatic compounds. However, it could be positive or negative for the production of aromatic compounds, which depended on the type of biomass in the feedstock. The significant removal of aldehydes, acids, ethers, furans, ketones, phenols and sugars from the final co-pyrolysis oil, in which there was a significant increase of alcohols, was achieved.

Non-conventional Yeast Species for Lowering Ethanol Content of Wines

Rising sugar content in grape must, and the concomitant increase in alcohol levels in wine, are some of the main challenges affecting the winemaking industry nowadays. Among the several alternative solutions currently under study, the use of non-conventional yeasts during fermentation holds good promise for contributing to relieve this problem. Non-Saccharomyces wine yeast species comprise a high number or species, so encompassing a wider physiological diversity than Saccharomyces cerevisiae. Indeed, the current oenological interest of these microorganisms was initially triggered by their potential positive contribution to the sensorial complexity of quality wines, through the production of aroma and other sensory-active compounds. This diversity also involves ethanol yield on sugar, one of the most invariant metabolic traits of S. cerevisiae. This review gathers recent research on non-Saccharomyces yeasts, aiming to produce wines with lower alcohol content than those from pure Saccharomyces starters. Critical aspects discussed include the selection of suitable yeast strains (considering there is a noticeable intra-species diversity for ethanol yield, as shown for other fermentation traits), identification of key environmental parameters influencing ethanol yields (including the use of controlled oxygenation conditions), and managing mixed fermentations, by either the sequential or simultaneous inoculation of S. cerevisiae and non-Saccharomyces starter cultures. The feasibility, at the industrial level, of using non-Saccharomyces yeasts for reducing alcohol levels in wine will require an improved understanding of the metabolism of these alternative yeast species, as well as of the interactions between different yeast starters during the fermentation of grape must.

Catalytic Reforming of Lignin-Derived Bio-Oil Over a Nanoporous Molecular Sieve Silicoaluminophosphate-11.

Catalytic pyrolysis of lignin, a major constituent of biomass, was performed. A nanoporous molecular sieve silicoaluminophosphate-11 (SAPO-11) was selected as catalyst. Thermogravimetric analysis showed that 500 degrees C was the optimal pyrolysis temperature. Pyrolyzer-gas chromatography/mass spectroscopy was used to investigate the pyrolysis product distribution. Production of phenolics, the dominant product from the pyrolysis of lignin, was promoted by the increase in the catalyst dose. In particular, low-molecular-mass phenolics were produced more over SAPO-11, while high-molecular-mass phenolics and double-bond-containing phenolics were produced less. The fraction of aromatic compounds, including benzene, toluene, xylene, and ethylbenzene, was also increased by catalytic reforming. The catalytic effects were more pronounced when the catalyst/biomass ratio was increased. The enhanced production of aromatic compounds by an acidic catalyst obtained in this study is in good agreement with the results of previous studies.

Catalytic conversion of biomass-derived sorbitol to aromatic compounds

ABSTRACTThe present wok is focused on a novel method of aromatic compounds production from biomass-derived sorbitol via catalytic processing. Aromatic compounds including substituted benzenes and olefins have been considered to be very promising in the substitution of diminishing fossil fuels since they are component of transportation fuels such as gasoline. The yield of aromatic compounds was found to be affected to a certain extent by reaction parameters and the catalyst. The effects of reaction parameters such as reaction temperature, weight hourly space velocity (WHSV), gas hourly space velocity (GHSV), and hydrogen pressure on the catalytic performance of the catalyst were investigated. The optimum reaction conditions were achieved as follows: 280°C of the temperature, 2.25 hr−1 of WHSV, 2000 hr−1 of GHSV, and 4.0 MPa of pressure. Meanwhile, the Ni/HZSM-5 catalyst modified by MCM-41 was selected to catalyze sorbitol into aromatic compounds. The testing results indicated that the catalyst containing metal centers and acid sites had the maximal activity with 100% of sorbitol conversion. Dehydration and aromatization of sorbitol was induced on the acidic sites of zeolite and its shape selectivity, whereas hydrogenation and cracking was carried out on those mental centers. The carbon distribution of the products was also close to the acidity of the catalyst.

DOMATES MEYVESİNİN BÜYÜME VE OLGUNLAŞMA SIRASINDA BİLEŞİMİNDE MEYDANA GELEN DEĞİŞİMLER

Tomato fruits have large amount of water content. The remaining contains carbohydrates, organic acids, vitamins, pigments, phenolic compounds and various mineral matters. During fruit growth and maturation dramatic changes in chemical composition of the fruit occur. Some of the important changes are degradation of starch, production in glucose and fructose, loss of chlorophyll, synthesis of pigments such as carotene and lycopene, increase in ratio of citric acid to malic acid, production of flavour and aroma compounds, breakdown of the toxic alkaloid tomatine and increase in glutamic acid. As a result of these ripening processes changes in colour in flavour and texture of fruit take place.

Ex-situ catalytic pyrolysis of citrus fruit peels over mesoporous MFI and Al-MCM-41

The thermal and ex-situ catalytic pyrolysis of different citrus peels, Citrus paradisi peel, Citrus sinensis peel, Citrus unshiu peel, and Citrus limon peel, were studied by thermogravimetric, evolved gas analysis–mass spectrometry and tandem micro-reactor–gas chromatograph/mass spectrometry analyses. Kinetic analysis revealed more complicated reaction steps and a wider range of activation energies of citrus peels than those of wood powder due to the presence of pectin in the citrus peels. Large amounts of methanol formation from each citrus peel were also recorded by evolved gas analysis–mass spectrometry and fast pyrolysis–gas chromatograph/mass spectrometry analyses at the main decomposition temperature of pectin, between 150 and 250°C. Mesoporous MFI was found to be a more effective catalyst for the production of mono aromatic compounds (benzene, toluene, ethylbenzene, and xylene; 3.06–4.17C%) and light olefins (ethene, propene, butene, and butadiene; 8.13–9.13C%) than Al-MCM-41 (mono aromatic compounds 0.67–0.93C% and light olefins 3.61–4.58C%) because of its higher catalytic activity in deoxygenation and aromatization due to the stronger acidity of mesoporous MFI. The yield of mono aromatic compounds over mesoporous MFI was highest from C. paradisi peel (4.17C%), followed in order by C. sinensis peel (3.83C%), C. unshiu peel (3.61C%), and C. limon peel (3.06C%), due mainly to the different contents and properties of pectin in each citrus peel. The higher activities of mesoporous MFI than Al-MCM-41 were also maintained during the 7 times sequential catalytic pyrolysis of C. paradisi peel, demonstrating the stability of mesoporous MFI catalyst.

Monitoring Volatile Aroma Compounds during Fermentation in a Chemically Defined Grape Juice Medium Deficient in Leucine

Model media are frequently used to study wine fermentation outcomes, as they are considered an acceptable and reproducible representation of real juices. Identifying and quantifying the progression of the aroma compounds formed during fermentation is of importance for studies aimed at tailoring winemaking outcomes. Overexpression libraries of the yeast Saccharomyces cerevisiae can be used to determine the impact of the overexpression of specific genes. Recently, an S. cerevisiae overexpression library has been reported that encompasses a plasmid-borne construct, which utilizes a leucine-selectable marker to differentiate between yeast that contain the plasmid and those that do not. As such, these experiments with this library require a leucine-deficient fermentation medium. Aroma-progression studies have been performed in real juice and in an MS300 model medium; however, to date, none have been performed in chemically defined grape juice medium (CDGJM) or in media lacking certain amino acids. This study reports on the progression of a library of 34 enologically relevant aroma compounds formed during fermentation using a leucine-requiring wine-strain derivative of S. cerevisiae bearing the overexpression library platform plasmid and grown in a CDGJM-Leu medium. The results indicate that the production and accumulation of all 34 aroma compounds followed similar progression trends to those found in previous studies with MS300 and juice-exploiting wild-type yeast, with the exception of the compounds associated with pathways connected to the biosynthesis and metabolism of leucine. The findings confirm the likely utility of this system for evaluating the importance of overexpression of specific genes in aroma-compound production.