Production Of Aromatic Compounds Research Articles

Transcriptional Comparison Investigating the Influence of the Addition of Unsaturated Fatty Acids on Aroma Compounds During Alcoholic Fermentation.

The levels of unsaturated fatty acids (UFAs) in grape must significantly influence yeast metabolism and the production of aroma compounds. In this work, cDNA microarray technology was applied to analyze the transcriptional discrepancies of wine yeast (commercial wine yeast Lalvin EC1118) fermenting in synthetic grape must supplemented with different concentrations of a mixture of UFAs (including linoleic acid, oleic acid, and α-linolenic acid). The results showed that the initial addition of a high level of UFAs can significantly enrich the intracellular UFAs when compared to a low addition of UFAs and further increase the cell population and most volatiles, including higher alcohols and esters, except for several fatty acids. Microarray analyses identified that 63 genes were upregulated, and 91 genes were downregulated during the different fermentation stages. The up-regulated genes were involved in yeast growth and proliferation, stress responses and amino acid transportation, while the repressed genes were associated with lipid and sterol biosynthesis, amino acid metabolism, TCA cycle regulation, mitochondrial respiration, and stress responses. Unexpectedly, the genes directly related to the biosynthesis of volatile compounds did not vary substantially between the fermentations with the high and low UFA additions. The beneficial aromatic function of the UFAs was ascribed to the increased biomass and amino acid transportation, considering that the incorporation of the additional UFAs in yeast cells maintains high membrane fluidity and increases the ability of the cells to resist deleterious conditions. Our results highlighted the importance of UFAs in the regulation of aroma biosynthesis during wine fermentation and suggested that the improvement of the resistance of yeast to extreme stresses during alcoholic fermentation is essential to effectively modulate and improve the production of aroma compounds. A potential way to achieve this goal could be the rational increase of the UFA contents in grape must.

Synthesis of an aromatic N-heterocycle derived from biomass and its use as a polymer feedstock

Aromatic N-heterocyclic compounds are very important chemicals, which are currently produced mostly from petroleum. Here we report that a pyridazine-based compound 6-(4-hydroxy-3-methoxyphenyl)pyridazin-3(2H)-one (GSPZ) can be efficiently synthesized by the Friedel-Crafts reaction of guaiacol and succinic anhydride, both of which can be derived from biomass. GSPZ is then treated with bio-based epichlorohydrin to prepare the epoxy resin precursor GSPZ-EP. With 4,4'-diaminodiphenylmethane as curing agent, GSPZ-EP possesses higher glass transition temperature (187 oC vs. 173 oC) and shows a 140%, 70 and 93% increase in char yield (in N2), storage modulus (30 oC) and Young’s modulus, respectively when compared with a standard petroleum-based bisphenol A epoxy resin. Moreover, the cured GSPZ-EP shows good intrinsic flame retardancy properties and is very close to the V-0 rating of UL-94 test. This work opens the door for production of aromatic N-heterocyclic compounds, which can be derived from biomass and employed to construct high performance polymers.

Operation parameters effect on yield and octane number for monometallic, bimetallic and trimetallic catalysts in naphtha reforming process

ABSTRACTNaphtha reforming is one of the vital catalytic operations in the petroleum industry due to the production of hydrogen and aromatic compounds. There are two ways to improve this process: try to design more efficient reactor setups and try to represent more efficient catalysts. Although catalyst deactivation is the inescapable phenomenon, the deactivation rate of different types of catalysts is not the same. The objective of this paper is to investigate the influence of various types of’ catalysts such as monometallic, bimetallic, and trimetallic catalysts, on the octane boosting process. Here, we have been focused on catalyst performance and deactivation patterns. Furthermore, we have been comparing activity, selectivity, and stability for monometallic, bimetallic and trimetallic catalysts. The results show the better activity, selectivity, and coke resistance of trimetallic in comparison with the monometallic and bimetallic catalysts.

Lactobacillus rhamnosus GG improves the sensorial profile of Camembert-type cheese: An approach through flash-profile and CATA

Camembert is a white-mould ripened cheese in which intense proteolysis, caused mainly by the fungus Penicillium candidum, among other factors, leads to a substantial production of aromatic and flavor compounds. The aim of this study was to evaluate the sensory profile of the Camembert-type cheese made from raw milk and from pasteurized milk with or without the addition of Lactobacillus rhamnosus GG. The cheeses were analyzed after 50 days of ripening through a combination of Flash-Profile (n = 15) and Check-All-That-Apply (CATA) (n = 80) sensory methods with global acceptance. The 51 sensory attributes obtained allowed the separation of the samples in three clusters. Through the CATA, a significant difference (p < 0.05) was observed for 21 of the 51 descriptors evaluated. Camembert-type cheese obtained from pasteurized milk with the addition of Lactobacillus rhamnosus GG showed greater global acceptance when compared to the other cheeses, which did not significantly differ between them. The addition of the adjunct culture was a good technological strategy to improve the sensory characteristics of industrial Camembert-type cheese obtained from pasteurized milk, bringing its sensory attributes closer to the ideal product and the sensorial characteristics of a cheese produced with raw milk, but in a standardized and microbiologically safe way.

Gas reforming and tar decomposition performance of nickel oxide (NiO)/SBA-15 catalyst in gasification of woody biomass

ABSTRACTIn the gasification of biomass, it is necessary to limit the amount of by-product tar and increase the yields of hydrogen (H2) and carbon monoxide (CO) (syngas). Therefore, we conducted gasification and reforming experiments on woody biomass using an electric tubular furnace, to evaluate the gas reforming and tar decomposition performance of a NiO/SBA-15 catalyst. As a result, we found that this catalyst is effective for H2 production. It is believed that the increase in H2 volume due to the catalyst occurs through a steam reforming reaction involving hydrocarbons, including methane (CH4), and the water-gas shift reaction. With respect to the influence of the gasifying agent on the reforming effect of the catalyst, the amount of generated carbon dioxide (CO2) and hydrogen (H2) increases because the shift reaction is promoted by supplying steam. On the other hand, it was inferred that the shift reaction rarely occurred because it approaches equilibrium by supplying O2. Furthermore, it is suggested that light aromatic hydrocarbons are decomposed by the catalyst.Implications: The mesoporous silica catalyst NiO/SBA-15 was highly effective for H2 production and decomposition of light aromatic compounds in the gasification of woody biomass. In the catalyst reaction, supplying steam promoted H2 production. From thermodynamic analysis and discussion, it was also inferred that supplying O2 might prevent the water gas shift reaction. The results are useful for designing a process needed for rich H2 production and gas refining process for further use of syngas.

A genome-scale metabolic network of the aroma bacterium Leuconostoc mesenteroides subsp. cremoris.

Leuconostoc mesenteroides subsp. cremoris is an obligate heterolactic fermentative lactic acid bacterium that is mostly used in industrial dairy fermentations. The phosphoketolase pathway (PKP) is a unique feature of the obligate heterolactic fermentation, which leads to the production of lactate, ethanol, and/or acetate, and the final product profile of PKP highly depends on the energetics and redox state of the organism. Another characteristic of the L. mesenteroides subsp. cremoris is the production of aroma compounds in dairy fermentation, such as in cheese production, through the utilization of citrate. Considering its importance in dairy fermentation, a detailed metabolic characterization of the organism is necessary for its more efficient use in the industry. To this aim, a genome-scale metabolic model of dairy-origin L. mesenteroides subsp. cremoris ATCC 19254 (iLM.c559) was reconstructed to explain the energetics and redox state mechanisms of the organism in full detail. The model includes 559 genes governing 1088 reactions between 1129 metabolites, and the reactions cover citrate utilization and citrate-related flavor metabolism. The model was validated by simulating co-metabolism of glucose and citrate and comparing the in silico results to our experimental results. Model simulations further showed that, in co-metabolism of citrate and glucose, no flavor compounds were produced when citrate could stimulate the formation of biomass. Significant amounts of flavor metabolites (e.g., diacetyl and acetoin) were only produced when citrate could not enhance growth, which suggests that flavor formation only occurs under carbon and ATP excess. The effects of aerobic conditions and different carbon sources on product profiles and growth were also investigated using the reconstructed model. The analyses provided further insights for the growth stimulation and flavor formation mechanisms of the organism.

Phytochemical Analysis of Ocimum americanum Linn. with Special Reference to the Impact of In vitro Flowering on the Production of Aromatic Compounds

Phytochemical Analysis of Ocimum americanum Linn. with Special Reference to the Impact of In vitro Flowering on the Production of Aromatic Compounds

Aroma formation in retentostat co-cultures of Lactococcus lactis and Leuconostoc mesenteroides

Lactococcus lactis subsp. lactis biovar diacetylactis and Leuconostoc mesenteroides are considered to be the main aroma producers in Dutch-type cheeses. Both species of lactic acid bacteria were grown in retentostat mono- and co-cultures to investigate their interaction at near-zero growth rates and to determine if co-cultivation enhances the aroma complexity compared to single species performance. During retentostat mono-cultures, the growth rates of both species decreased to less than 0.001 h−1 and a large fraction of the cells became viable but not culturable. Compared to Lc. mesenteroides, L. lactis reached a 3.4-fold higher biomass concentration caused by i) a higher ATP yield on substrate, ii) a higher biomass yield on ATP and iii) a lower maintenance requirement (mATP). Dynamic models estimated that the mATP of both species decreased approximately 7-fold at near-zero growth rates compared to high growth rates. Extension of these models by assuming equal substrate distribution resulted in excellent prediction of the biomass accumulation in retentostat co-cultures with L. lactis dominating (100:1) as observed in ripened cheese. Despite its low abundance (∼1%), Lc. mesenteroides contributed to aroma production in co-cultures as indicated by the presence of all 5 specific Lc. mesenteroides compounds. This study provides insights in the production of cheese aroma compounds outside the cheese matrix by co-cultures of L. lactis and Lc. mesenteroides, which could be used as food supplements in dairy or non-dairy products.

Acetate-ester hydrolase activity for screening of the variation in acetate ester yield of Cyberlindnera fabianii, Pichia kudriavzevii and Saccharomyces cerevisiae

Esters constitute an important class of aroma compounds and contribute significantly to the aroma of yeast-fermented beverages. Ester formation is well studied in Saccharomyces cerevisiae, while production of aroma compounds by non-conventional yeasts has received little attention. The selection of such strains for co-culturing with S. cerevisiae offers opportunities for product innovations. Therefore, we performed a comparative analysis of the diversity in ester production by Cyberlindnera fabianii 65 (Cf65), Pichia kudriavzevii 129 (Pk129) and S. cerevisiae 131 (Sc131). For all three species distinct aroma profiles were identified, with Cf65 producing the highest amount of acetate esters. Since esters are formed from alcohols and acyl-CoA or acetyl-CoA, we analysed in vitro alcohol dehydrogenase and alcohol acetyl transferase activities in those three yeasts and found no correlation with ester formation. In contrast, a clear inverse correlation between the acetate-ester hydrolase activity and acetate ester yield was found for the three yeast species. Our study indicates that acetate-ester hydrolase activity plays a key role in determination of the final amount of acetate esters in fermentation broths.

Pre-fermentative supplementation of fatty acids alters the metabolic activity of wine yeasts

Fatty acids play important roles in the maintenance of cell membrane, viability and overall metabolism of wine yeasts (particularly Saccharomyces cerevisiae) during adverse winemaking conditions. We previously showed that linoleic acid supplementation markedly affect aroma compound production of S. cerevisiae wine strains. However, very little is known about how other commonly found fatty acids in grape juice modulate the growth and metabolism of S. cerevisiae. We aimed to determine the individual effect of five fatty acids on fermentation patterns and metabolism of two wine yeast strains (S. cerevisiae EC1118 and X5). Microvinification was performed at 15 °C by supplementing a grape juice (individually) with three different concentrations of saturated (palmitic acid), unsaturated (oleic, linoleic and γ-linolenic acids) and short-chain (hexanoic acid) fatty acids. Metabolite profiles of the resulting wines were determined using Gas-chromatography coupled to Mass-spectrometry (GC–MS). Our data show that the addition of γ-linolenic acid to the juice caused the production of higher amounts of amino and organic acids (except isoleucine and 2-oxoglutaric acid) in wines when fermented by EC1118, while palmitic acid supplementation showed similar trends when fermented by X5. The effect of linoleic acid was independent of yeast strains and we observed a global reduction of amino and organic acids (except pyruvic acid) while increased production of most of the fatty acids other than the supplemented ones. Our data clearly suggest that pre-fermentative supplementation of different fatty acids indeed influenced the growth and metabolism of wine yeasts in a different way. Thus, attention needs to be paid not only to the wine yeast strain used during the winemaking but also to the overall grape juice composition, including fatty acids, to obtain the desired wine characteristics.

Production of Aliphatic and Aromatic Compounds in the High Temperature Decomposition of Propargyl Chloride. Single Pulse Shock Tube Experiments, Quantum Chemical Calculations, and Computer Modeling.

The thermal reactions of propargyl chloride were studied behind reflected shock waves in a pressurized driver 2 in. i.d. single-pulse shock tube over the temperature range 1000-1350 K and pressure range behind the reflected shocks of 2-4 atm. Cooling rates were ∼5 × 105 K/s. The reflected shock temperatures were calculated from the extent of elimination of hydrofluoric acid (HF) from 1,1,1-trifluoroethane, where 1,1,1-trifluoroethane (TFE) → HF + 1,1-difluoroethylene (DFE), that was added in small concentration (0.1%) to the reaction mixture to serve as a chemical thermometer. For comparison, the shock temperatures were obtained also from the measured incident shock velocities, using the three conservation equations and the ideal gas equation of states. Fifteen stable reaction products, containing different numbers of carbon atoms (from two to nine), both aliphatic and aromatic, chain and cyclic, with and without chlorine resulting from the initial rupture of the C-Cl bond in propargyl chloride were identified. On the basis of the results of quantum chemical calculations that were carried out, a chemical kinetic scheme containing 63 elementary steps was constructed. Comparison of the curves that were calculated by using the kinetic scheme with the experimental results shows good agreement.

Aroma Profile Analyses of Filamentous Fungi Cultivated on Solid Substrates.

Filamentous fungi have been used since centuries in the production of food by means of solid substrate fermentation (SSF). The most applied SSF involving fungi is the cultivation of mushrooms, e.g., on tree stumps or sawdust, for human consumption. However, filamentous fungi are also key players during manufacturing of several processed foods, like mold cheese, tempeh, soy sauce, and sake. In addition to their nutritive values, these foods are widely consumed due to their pleasant flavors. Based on the potentials of filamentous fungi to grow on solid substrates and to produce valuable aroma compounds, in recent decades, several studies concentrated on the production of aroma compounds with SSF, turning cheap agricultural wastes into valuable flavors. In this review, we focus on the presentation of common analytical methods for volatile substances and highlight various applications of SSF of filamentous fungi dealing with the production of aroma compounds. Graphical Abstract.

Experimental Study of Destructive Distillation of Maiganga Coal: Analysis of Products’ Yield and Composition

The research involves destructive distillation of Maiganga coal, analysis of the yields and characterization of condensable products. Maiganga coal was distillated in a pyrolyser, the condensable products were recovered in a three stage separator, and the products were collected over a range of temperatures. The yields’ of the char was obtained by measuring the weight of the char and then divided by the starting weight of the coal sample. The condensable products yields were obtained in similar manner as the char. The yield of the gaseous product was obtained by subtracting the sum of yields of char and condensable products from unity. The yields of semi-coke, water and tar were 63, 11, and 7%, respectively. The tar obtained was characterize using GC/MS to determine the chemical composition. The characterization was carried out using Agilent Gas Chromatography/ Mass Selective Detector (GC/MSD). The GC/MSD results show that the dominant compounds in the tar are aromatic, acid, and esters. However sulphur, nitrogen, chlorine, and fluorine compounds were present. The specific dominant compound is Benzeneacetic acid, 4-tetradecyl ester, (C₂₂H₃₆O₂) about 33%, and the least were 1H-Thiopine, 2,3,6,7-tetrahydro-4,5-didehydro-3,3,6,6-tetramethyl (C₁₀H₁₆OS), 1-oxide, 4-(2,5-Dihydro-3-methoxyphenyl)butylamine (C₁₁H₁₉NO) about 6%. The coal may serve as feedstock for production of coke and aromatic compounds.

Stl1 transporter mediating the uptake of glycerol is not a weak point of Saccharomyces kudriavzevii's low osmotolerance

Saccharomyces kudriavzevii is a nonconventional and rather osmosensitive yeast with a high potential of use in fermentation processes. To elucidate the basis of its relative osmosensitivity, the role of the STL1 gene encoding a putative glycerol uptake system was studied. Under higher osmotic pressure, the addition of a low amount of glycerol to the growth medium improved the growth of S. kudriavzevii and the expression of the STL1 gene was highly induced. Deletion of this gene decreased the strain's ability to grow in the presence of higher concentrations of salts and other solutes. Moreover, the mutant had a disturbed homeostasis of intracellular pH. Expression of the SkSTL1 gene in Saccharomyces cerevisiae complemented the osmosensitivity of the S. cerevisiae hog1Δ stl1Δ mutant, and the gene's tagging with GFP localized its product to the plasma membrane. Altogether, a deficiency in glycerol uptake did not seem to be the reason for S. kudriavzevii's low osmotolerance; its Stl1 transporter properly contributes to the regulation of intracellular pH and is crucial to its survival of osmotic stress. SIGNIFICANCE AND IMPACT OF THE STUDY: An increasing demand for food products with benefits for human health turns the attention to less-exploited nonconventional yeasts with interesting traits not found in Saccharomyces cerevisiae. Among them, Saccharomyces kudriavzevii has good potential for aroma-compound production, fermentations and other biotechnological applications, but it is less adapted to stressful industrial conditions. This report studied S. kudriavzevii relative osmosensitivity and its capacity for active glycerol uptake. The results obtained (on the activity and physiological function of S. kudriavzevii glycerol transporter) may contribute to a further engineering of this species aiming to improve its osmotolerance.

The molecular biology of fruity and floral aromas in beer and other alcoholic beverages.

Aroma compounds provide attractiveness and variety to alcoholic beverages. We discuss the molecular biology of a major subset of beer aroma volatiles, fruity and floral compounds, originating from raw materials (malt and hops), or formed by yeast during fermentation. We introduce aroma perception, describe the most aroma-active, fruity and floral compounds in fruits and their presence and origin in beer. They are classified into categories based on their functional groups and biosynthesis pathways: (1) higher alcohols and esters, (2) polyfunctional thiols, (3) lactones and furanones, and (4) terpenoids. Yeast and hops are the main sources of fruity and flowery aroma compounds in beer. For yeast, the focus is on higher alcohols and esters, and particularly the complex regulation of the alcohol acetyl transferase ATF1 gene. We discuss the release of polyfunctional thiols and monoterpenoids from cysteine- and glutathione-S-conjugated compounds and glucosides, respectively, the primary biological functions of the yeast enzymes involved, their mode of action and mechanisms of regulation that control aroma compound production. Furthermore, we discuss biochemistry and genetics of terpenoid production and formation of non-volatile precursors in Humulus lupulus (hops). Insight in these pathways provides a toolbox for creating innovative products with a diversity of pleasant aromas.

Genome Sequence of the Wine Yeast Saccharomycodes ludwigii UTAD17.

This work describes, for the first time, the genome sequence of a Saccharomycodes ludwigii strain. Although usually seen as a wine spoilage yeast, S. ludwigii has been of interest for the production of fermented beverages because it harbors several interesting properties, including the production of beneficial aroma compounds.

Gut Microbiome in Critical Illness (Review)

Radical changes in the composition, diversity and metabolic activity of gut microbiome in critically ill patients most probably affect adversely the outcome of treatment. Microbiota dysfunction may be a predictor and presumably the main cause of infectious complications and sepsis. Clinicists use objective scales for evaluation of patient condition severity including specific parameters of disorders of organs and systems; however, microbiota function is not considered specific and, hence, not evaluated. Technical capabilities of the recent decade have allowed characterizing the intestinal microbiota and that helped understanding the ongoing processes. The authors have analyzed data about the role of intestinal microbiota as a metabolic 'reactor' during critical states, possible complications related to misbalance of 'harmful' and 'beneficial' bacteria, and examined potential of a targeted therapy aimed directly at correction of intestinal microbiota. Search for papers was carried out using Scopus and Web of Science databases 2001 to 2018 years: (Gut Microbiota) AND (Critically ill OR Intensive care unit), key words taken for the search were: intestinal microbiota, metabolism, sepsis, antibiotics, critically ill patients, multiple organ failure. A number of questions in understanding of the interaction between gut microbiome and host remain open. It is necessary to take into account interference of microbial metabolism while assessing metabolome of patients with sepsis. Among low-molecular compounds found in blood of sepsis patients, special attention should be paid to molecules that can be classified as ‘common metabolites’ of humans and bacteria, for example, degradation products of aromatic compounds, which many-fold rise in blood of septic patients. It is necessary to take into consideration and experimentally model changes in the human internal environment, which occur during radical transformation of microbiome in critically ill patients. Such approach brings in new prospects for objective monitoring of diseases by evaluating metabolic profile at a particular moment of time based on integral indices reflecting the status of microbiome/metabolome system, which will supply new targets for therapeutic intervention in future.

Influence of catalyst bed temperature and properties of zeolite catalysts on pyrolysis-catalysis of a simulated mixed plastics sample for the production of upgraded fuels and chemicals

The pyrolysis-catalysis of a simulated mixture of plastics representing the plastic mixture found in municipal solid waste has been carried out to determine the influence of process conditions on the production of upgraded fuel oils and chemicals and gases. The catalysts used were spent zeolite from a fluid catalytic cracker (FCC), Y-zeolite and ZSM-5 zeolite. The addition of a catalyst to the process produced a marked increase in gas yield, with more gas (mainly C1–C4 hydrocarbons) being produced as the temperature of the catalyst was raised from 500 °C to 600 °C. The Si/Al ratio of the catalysts influenced the composition of other gases with the more basic catalysts producing more CO and the strongly acidic catalyst producing more H2. The yield of product oil decreased with the addition of the catalysts, but the oil was of significantly lower molecular weight range, containing a product slate of premium fuel range C5–C15 hydrocarbons. In addition, the content of aromatic compounds in the product oil was increased; for example, benzene and toluene accounted for more than 90% of the aromatic content of the oil from the strongly acidic Y-zeolite catalysts. A reaction scheme is proposed for the production of single-ring aromatic compounds via pyrolysis-catalysis of plastics.

Alternation of aroma and flavor profiles in biscuits by an enzymatic approach

Bromelain is a complex protease existing in both the fruits and the stems of pineapple plants. Bromelain from these two parts of pineapple plants exhibits different characteristics. Stem bromelain has been extensively investigated and is commercially available for applications in various industries. On contrast, studies on fruit bromelain are quite limited. Here we investigated the effects of fruit bromelain on production of biscuits aroma and flavor compounds. The fruit bromelain was first isolated from pineapple fruit, activity assayed, purity of enzyme determined and then added into dough. Biscuits aroma and flavor compounds were identified by HS-SPME combined with GC-MS. Results showed that aroma and flavor compounds of biscuit varied in terms of amount and varieties.

High PAH degradation and activity of degrading bacteria during alfalfa growth where a contrasted active community developed in comparison to unplanted soil.

PAH biodegradation in plant rhizosphere has been investigated in many studies, but the timescale of degradation and degrading bacteria activity was rarely considered. We explored the impact of plants on the temporal variability of PAH degradation, microbial abundance, activity, and bacterial community structure in a rhizotron experiment. A historically contaminated soil was spiked with PAHs, planted or not with alfalfa, over 22days with sampling once a week. In both conditions, most of the spiked PAHs were dissipated during the first week, conducting to polar polycyclic aromatic compound production and to decreased richness and diversity of bacterial communities. We showed a rapid impact of the rhizosphere on PAH degradation via the increased activity of PAH-degrading bacteria. After 12days, PAH degradation was significantly higher in the planted (100% degradation) than in unplanted (70%) soil. Gram-negative (Proteobacteria) PAH-dioxygenase genes and transcripts were higher in planted than unplanted soil and were correlated to the spiked PAH degradation. Conversely, Gram-positive (Actinobacteria) PAH-dioxygenase gene transcription was constant over time in both conditions. At 12days, plant growth favored the activity of many Gammaproteobacteria (Pseudomonadaceae, Stenotrophomonas, and Acinetobacter) while in unplanted soil Alphaproteobacteria (Sphingomonadaceae, Sphingobium, and Magnetospirillum) and Actinobacteria (Iamia, Geodermatophilaceae, and Solirubrobacterales) were more active.