Pyrazines: occurrence, formation and biodegradation

Simultaneously Mitigation of Acrylamide, 5-Hydroxymethylfurfural, and Oil Content in Fried Dough Twist via Different Ingredients Combination and Infrared-Assisted Deep-Frying

The effect of main ingredients (wheat flours, polyol sweeteners, and frying oil) and infrared-assisted deep-frying on the acrylamide, 5-hydroxymethylfurfural (HMF), oil content, and physicochemical characteristics of fried dough twist (FDT) were investigated. The amount of acrylamide and HMF produced in FDT made with low-gluten flour is significantly lower than that of flour with high gluten content. Among polyol sweeteners, maltitol causes the greatest reduction in acrylamide and HMF in FDT. Moreover, the oil content of FDT was significantly reduced by optimizing the infrared-assisted deep-frying process. At last, compared with deep-frying FDT made of sucrose, infrared-assisted deep-frying FDT made of maltitol reduced acrylamide, HMF, and oil content by 61.8%, 63.4%, and 27.5%, respectively. This study clearly showed that the ingredients, flour and polyol sweeteners used to process FDT are the two major determinants of the formation of acrylamide and HMF in FDT, and infrared-assisted deep-frying can significantly affect the oil content in FDT. Simultaneously, the mitigation of the acrylamide, HMF, and oil content in FDT can be achieved by using low-gluten flour and maltitol in the ingredients, combined with infrared-assisted deep-frying.

Microbial diversity and chemical characteristics of Coffea canephora grown in different environments and processed by dry method

This study aimed to assess the microbial diversity in Coffea canephora grown in four different environments of Espirito Santo state, Brazil. Coffee cherries of two different altitudes (300 and 600 m) and two terrain aspects (Southeast-facing and Northwest-facing slopes) were processed by the dry method. Samples were collected during the drying/fermentation process. Microorganisms were counted, isolated, and identified by MALDI-TOF, followed by sequencing of the ribosomal region. Sugars and organic acids were quantified by HPLC and volatile compounds of the roasted coffees were evaluated by GC-MS. Bacteria population presented a significant number of isolates as well as higher counts during the drying/fermentation process with respect to the population of yeasts. The principal genera of microorganisms found were Bacillus, Pichia, Candida, and Meyerozyma. Meyerozyma guilliermondii was the most frequent yeast in all environments. On the other hand, Pichia kluyveri was found only in coffee cherries from the 600 m altitude. The highest concentration of acetic and succinic acids observed was 6.06 mg/g and 0.84 mg/g, respectively. Sucrose concentrations ranged from 0.68 to 5.30 mg/g, fructose from 1.30 to 4.60 mg/g, and glucose from 0.24 to 1.25 mg/g. Thirty-six volatile compounds, belonging to the groups of pyrazines, alcohols, aldehydes, ketones, and furans were identified in roasted coffee, with differences between altitude and terrain aspects. Information about microbial diversity is crucial to better understand the coffee quality and distinct characteristics of coffee produced in different environments.

Dealing with soy sauce precipitation at submicron-/nano-scale: An industrially feasible approach involving enzymolysis with protease and alkaline conditions

This study proposes an industrially feasible approach to handle the heating-induced soy sauce precipitates (SSPs) during soy sauce production. Protein (32.59%; containing a large amount of hydrophobic amino acid) and sugar (26.86%) were found to be the main composition of SSPs, and high content of mineral elements were also discovered in SSPs. A pH adjustment to 8-12 along with an enzymolysis step with alkaline protease seemed beneficial for this purpose while offering opportunities to manipulate the soy sauce quality. The pH adjustment decreased SSPs particle size from micron-scale to submicron- or nano-scale, and improved significantly the efficiency of SSPs protein enzymatic hydrolysis and protein recovery (up to 80%). The enzymolysis with alkaline protease enabled the generation of pyrazines while affecting the contents of phenols, alcohols, furans, pyrroles and sulfur-containing compounds. Interactions occurred between amino acids and sugars, among volatiles, and between volatiles (like aldehydes) and other monomers under such alkaline conditions. This study presents an efficient approach that is of practical significance to dealing with SSPs in soy sauce production and reuse of SSPs.

Pyrazines: A diverse class of earthy-musty odorants impacting drinking water quality and consumer satisfaction

The presence of earthy-musty odors in drinking water is a major concern for water suppliers and consumers worldwide. While geosmin and 2-methylisoborneol are the most studied earthy-musty odor-causing compounds, pyrazine and its alkyl and methoxy compounds possess similar odors and are widely distributed in nature, foods, and beverages. In this study, odor characteristics of pyrazines and their presence in natural and treated waters were determined. Pyrazine, 2,6-dimethyl-pyrazine (DMP), 2,3,5-trimethyl-pyrazine (TrMP), 2-ethyl-5(6)-methyl-pyrazine (EMP), 2,3,5,6-tetramethyl-pyrazine (TeMP), 2-isobutyl-3-methoxy-pyrazine (IBMP) and 2-isopropyl-3-methoxy-pyrazine (IPMP) were measured in source and finished drinking water across China. 2-Methoxy-3,5-dimethyl-pyrazine (MDMP), IBMP, and IPMP were investigated in rivers in Virginia, USA. The results showed that "musty" and "sweet" were the most common descriptors for pyrazine, DMP, MDMP, TrMP, and TeMP. While IBMP and IPMP were never detected in 140 source or drinking water samples from across China, pyrazine, DMP, MDMP, TrMP, and TeMP occurred throughout with concentrations of n.d.-62.2 ng/L-aq in source water and n.d.-39.6 ng/L-aq in finished water. IBMP, IPMP, and MDMP were present in two Virginia rivers; MDMP occurred in 18% of the samples with concentrations of n.d.-4.4 ng/L, many of which were above the aqueous odor threshold of 0.043 ng/L MDMP. The removal efficiencies through conventional water treatment were poor, ranging from negative removals to ∼10%. Advanced oxidation water treatment could only remove EMP and TrMP. The widespread presence of earthy-musty-sweet pyrazines in source and drinking waters on two continents, their poor removal during water treatment, and ng/L odor threshold concentrations confirm their potential to be T&O issues for consumers.

Modelling flavour formation in roasted malt substrates under controlled conditions of time and temperature

Drum roasted products are used to impart colour, flavour and mouthfeel to beers. Here we designed a laboratory-scale roaster (100 g batch size) capable of precise time-temperature control and investigated the impacts of time, temperature and roasting substrate (barley, pale malt or germinated green malt) on formation of 20 key odour active aroma volatiles. Principal Components Analysis (PCA) of flavour volatile data across 37 laboratory roasted and 6 commercial roasted products generated a product flavour space depicting the relationship between roasting conditions and concentrations of these 20 compounds. Response surface models were produced for aroma compound concentrations across the design space of roasting times and temperatures for each substrate. These clearly illustrate the impacts of substrate moisture content and prior history (e.g. whether germinated or germinated and kilned) on flavour formation. In low moisture substrates a steep increase in associated heterocyclic aroma compound production was noted at process temperatures >180 °C.

Volatile compounds, physicochemical and sensory characteristics of Colatura di Alici, a traditional Italian fish sauce

BACKGROUND

The present study reports for the first time the physical, chemical and sensory characterization of a traditional fish sauce from Italy, called 'Colatura di Alici', which is considered to be the direct descendant of the ancient roman sauce 'Garum'.

RESULTS

Among the volatile compounds, carboxylic acids, aldehydes, sulphuric compounds and pyrazines were identified. The most abundant compounds identified were 3-methyl-butanoic acid, nonanal and 3-methyl-butanal. The sample A had the highest amount of volatile fatty acids (>250 μg kg^-1 ) and sample B had the highest concentration of aldehydes (>80 μg kg^-1 ). These volatile compounds arise from the long fermentation activity and oxidation of fatty acids of the fish flesh and are responsible for the strong cheesy and fishy aroma. The protein content ranged from 90 to 130 g kg^-1 , and the soluble solids ranged from 30 to 38 °Brix, as a result of the high amount of NaCl used during processing. The sensory analysis showed a great intensity for the cheesy, fishy and umami attributes, and a medium intensity for the roasted and meaty attributes.

CONCLUSION

For the first time, the volatile compounds and sensory characteristics of this traditional fish sauce are reported. The samples differ in terms of sensory and aromatic profiles. These differences are probably linked to the poorly standardized methods used in the production process. Overall, the results of the present study could be used by local fish sauce producers to monitor the quality of the product and to improve the production process. © 2020 Society of Chemical Industry.

Antifungal Effects of Volatiles Produced by Bacillus subtilis Against Alternaria solani in Potato

Antifungal activities of plant-beneficial Bacillus have been widely studied in recent years. Numerous studies have studied the antifungal mechanisms of soluble non-volatile bioactive compounds such as lipopeptides and proteins produced by Bacillus against soil-borne diseases. However, the antagonistic mechanisms of volatile organic compounds (VOCs) from Bacillus against airborne phytopathogens are still largely unknown, and the function of Alternaria solani pathogenic genes has not been well identified. Here, we first isolated a Bacillus strain with strong antifungal activity and finally identified it as B. subtilis ZD01. Then, the antagonistic mechanisms of VOCs produced by strain ZD01, against A. solani, an airborne fungal pathogen that can cause early blight diseases of potato, were studied. We showed that VOCs produced by strain ZD01 can reduce the colony size and mycelial penetration and can cause serious morphological changes of A. solani. Scanning electron microscope (SEM) observation showed that VOCs released by ZD01 could cause more flaccid and gapped hyphae of A. solani. Also, we found that VOCs produced by ZD01 can inhibit the conidia germination and reduce the lesion areas and number of A. solani in vivo significantly. Meanwhile, based on gas chromatography/mass spectrometry (GC/MS) analysis, 29 volatile compounds produced by strain ZD01 were identified. Out of 29 identified VOCs, 9 VOCs showed complete growth inhibition activities against A. solani. Moreover, we identified two virulence-associated genes (slt2 and sod) in A. solani. slt2 is a key gene that regulates the mycelial growth, penetration, sporulation, and virulence in vivo in A. solani. In addition, sod plays a significant role in the SOD synthetic pathway in A. solani. Results from qRT-PCR showed that the transcriptional expression of these two genes was down-regulated after being treated by VOCs produced by ZD01. These results are useful for a better understanding of the biocontrol mechanism of Bacillus and offer a potential method for potato early blight disease control.

Comparison of volatile trapping techniques for the comprehensive analysis of food flavourings by Gas Chromatography-Mass Spectrometry

Trapping volatiles is a convenient way to study aroma compounds but it is important to determine which volatile trapping method is most comprehensive in extracting the most relevant aroma components when investigating complex food products. Awareness of their limitations is also crucial. (Un)targeted metabolomic approaches were used to determine the volatile profiles of two commercial flavourings. Four trapping techniques were tested as was the addition of salt to the mixture. Comprehensiveness and repeatability were compared and SBSE proved particularly suitable for extracting components such as polysulfides, pyrazines and terpene alcohols, and provided an overall broader chemical spectrum. SPME proved to be more suitable in extracting sesquiterpenes and DHS in extracting monoterpenes. Adding salt to the sample had only quantitative effects on volatiles as detected by SPME. These results help clarify the advantages and limitations of different trapping techniques and hence deliver a valuable decision tool for food matrix analysis.

Preparation of high-quality concentrated fragrance flaxseed oil by steam explosion pretreatment technology

In this study, flaxseed was pretreated by steam explosion technology and subsequently pressed to prepare flaxseed oil. GC, UPLC, HPLC, and GC-MS techniques were used to analyze the quality characteristics of the prepared flaxseed oil. These included the food safety risk indices, micronutrient components, and oxidative stability. The effects of different steam explosion pressures on the quality characteristics and relative volatile components of flaxseed oil were also investigated. The results revealed that steam explosion pretreatment technology could significantly increase the oil yield, improve micronutrient content, and strengthen the oxidation stability of the product. Moreover, the food safety risk indices (e.g., benzopyrene) were controlled within a reasonable range, while the fatty acid content remained almost unchanged. Notably, the relative pyrazine content in the total volatile components of flaxseed oil was 68.25% when the steam explosion pressure reached 1.2 MPa. This was considered as the main factor that contributed to the unique concentrated fragrance of the produced flaxseed oil. To prove the superiority of the steam explosion pretreatment, we compared this technique with traditional high-temperature roasting and popular microwave pretreatment techniques. The results revealed that flaxseed oil prepared by steam explosion pretreatment displayed the best quality characteristics and most concentrated fragrance. Thus, steam explosion technology shows great potential for application to produce high-quality concentrated fragrance flaxseed oil. This study provides significant reference and guidance for the preparation process of flaxseed oil.

Characterizing the effect of packaging material and storage temperature on the flavor profiles and quality of soy sauce

The effect of packaging material and storage temperature on two types of soy sauce was investigated. Ethanol content decreased significantly in all tested samples after storage (P < 0.05). While the changes of physicochemical properties and CIELAB color space indexes varied with soy sauce types, packaging materials and storage temperatures. The changes of volatile profiles after storage indicated that storage temperature was a key factor resulting in flavor scalping. It also suggested that there was no significant difference of flavor compounds sorption between glass bottle and polyethylene terephthalate bottle. The abundances of acids and alcohols increased after stored at ambient temperature (AT) and low temperature (LT) for 90 days, but phenols decreased. The effect of the packaging material, raw soy sauce type and storage temperature resulted in changing the intensities of fruity, caramel-like, mushroom-like note as well as smoky note. For the inoculated soy sauces, 1-octen-3-ol, ethyl hexanoate and ethyl octanoate in the samples were dominant in samples stored at AT, while the samples stored at LT were characterized by multiple components according to the results of principal components analysis. These results were benefit for understanding the main factors affecting the flavor profiles and quality of soy sauce during storage, as well as optimizing the storage condition.

Enhanced Production of Tetramethylpyrazine in Bacillus licheniformis BL1 through aldC Over-expression and acetaldehyde Supplementation

Bacillus licheniformis BL1 was used as a starting strain to construct the recombinant tetramethylpyrazine (TMP)-producing strains by over-expression of the α-acetolactate decarboxylase gene (aldC) and α-acetolactate synthase gene (alsS), named BLC, BLS and BLCS, respectively. Then the addition of acetaldehyde was use to enhance the TMP yield in the fermentation process. During microaerobic fermentation, the aldC-overexpressed BLC strain produced 43.75 g TMP/L which was 15.47% higher than the TMP in culture yielded using the initial BL1 strain. Furthermore, the acetoin yield as TMP precursor similarly rose by 23.06% in BLC recombinant strain. In contrast, the 2,3-BD increased by 23.2% in the recombinant BLCS. TMP produced by BL1 could be bolstered via the supplementation of the acetaldehyde in fermentation medium. This method also has the same effect on the BLC strain.

Comparison of the phenolic contents, antioxidant activity and volatile compounds of different sorghum varieties during tea processing

BACKGROUND

Sorghum grain is rich in phenolic compounds and has the potential to be developed into functional beverages such as sorghum grain tea, in which the health benefits and flavour are the important quality attributes to be considered in tea product development. Therefore, this study investigated the effect of grain tea processing steps on the phenolic contents, antioxidant activity and aroma profile (volatile compounds) of MR-Buster (red-coloured) and Shawaya Short Black 1 (black-coloured) sorghum and the results compared with those for our previously reported Liberty (white-coloured) sorghum.

RESULTS

Tea processing had significant impacts on sorghum polyphenols and volatile compounds, but the effect and level varied among sorghum varieties. The phenolic contents and antioxidant activity in these three sorghum varieties were consistent in both raw grain and grain tea samples and in the order Shawaya Short Black 1 > MR-Buster > Liberty. However, the volatile profiles (both individual and grouped volatiles) were significantly different between sorghum varieties, and the abundance and diversity of the volatile compounds of the tea samples were in the order Liberty > MR-Buster > Shawaya Short Black 1.

CONCLUSIONS

Black-coloured sorghum with high phenolic content and antioxidant activity is more suitable for making sorghum tea considering the health benefits. In terms of the aroma intensity and diversity, white-coloured sorghum could be the ideal material. However, future study is needed to determine the key volatile compounds that positively contribute to the aroma. This work provides important insights into the selection of grain materials for sorghum grain tea production. © 2019 Society of Chemical Industry.

Exploring the detailed spectroscopic characteristics, chemical and biological activity of two cyanopyrazine-2-carboxamide derivatives using experimental and theoretical tools

This article represents the spectroscopic and computational studies of two new pyrazine compounds. In order to establish the structure and functional nature of the compounds, we have employed Fourier transformed infrared (FT-IR) and Raman spectra, nuclear magnetic resonance (NMR) spectra, and ultraviolet (UV) absorptions and have compared them with the simulated computational spectra and found that they are in the agreeable range. Simulated hyperpolarisability values are used to obtain the nonlinear optic (NLO) activity of the compound, to be used in organic electronic materials. The charge transfer and related properties was investigated by the simulation of electronic spectrum with time dependent density functional theory (TD-DFT). Natural transition orbitals (NTO) provides information about which region of the molecules are more involved in the electronic transitions and the charge transfer properties for the lowest energy excitation have been analyzed on the basis of electron density variation. Molecular dynamics simulations provide information about the behavior of the molecule in solutions. Frontier orbital analysis and study of various reactivity descriptors like ALIE and Fukui provided deep knowledge on the reactivity side. Molecular docking has been also performed to investigate the interaction between title molecules and exhibits inhibitory activity against Pseudomonas aeruginosa Enoyl-Acyl carrier protein reductase (Fabl).

Synthesis, structure and photoluminescence properties of three copper(i) iodide based inorganic–organic hybrid structures with pyrazine derivatives

By using pyrazine derivatives, three different types of copper(i) iodide based inorganic–organic hybrid structures have been prepared.

Significance and Transformation of 3-Alkyl-2-Methoxypyrazines Through Grapes to Wine: Olfactory Properties, Metabolism, Biochemical Regulation, and the HP-MP Cycle

3-Alkyl-2-methoxypyrazines (MPs) contribute to the herbaceous flavor characteristics of wine and are generally considered associated with poor-quality wine. To control the MPs in grapes and wine, an accurate understanding of MP metabolism is needed. This review covers factors affecting people in the perception of MPs. Also, the history of O-methyltransferases is revisited, and the present review discusses the MP biosynthesis, degradation, and biochemical regulation. We propose the existence of a cycle between MPs and 3-alkyl-2-hydropyrazines (HPs), which proceeds via O-(de)methylation steps. This cycle governs the MP contents of wines, which make the cycle the key participant in MP regulation by genes, environmental stimuli, and microbes. In conclusion, a comprehensive metabolic pathway on which the HP-MP cycle is centered is proposed after gaining insight into their metabolism and regulation. Some directions for future studies on MPs are also proposed in this paper.

An Alkylpyrazine Synthesis Mechanism Involving l-Threonine-3-Dehydrogenase Describes the Production of 2,5-Dimethylpyrazine and 2,3,5-Trimethylpyrazine by Bacillus subtilis

Alkylpyrazines are important contributors to the flavor of traditional fermented foods. Here, we studied the synthesis mechanisms of 2,5-dimethylpyrazine (2,5-DMP) and 2,3,5-trimethylpyrazine (TMP). Substrate addition, whole-cell catalysis, stable isotope tracing experiments, and gene manipulation revealed that l-threonine is the starting point involving l-threonine-3-dehydrogenase (TDH) and three uncatalyzed reactions to form 2,5-DMP. TDH catalyzes the oxidation of l-threonine. The product of this reaction is l-2-amino-acetoacetate, which is known to be unstable and can decarboxylate to form aminoacetone. It is proposed that aminoacetone spontaneously converts to 2,5-DMP in a pH-dependent reaction, via 3,6-dihydro-2,5-DMP. 2-Amino-3-ketobutyrate coenzyme A (CoA) ligase (KBL) catalyzes the cleavage of l-2-amino-acetoacetate, the product of TDH, into glycine and acetyl-CoA in the presence of CoA. Inactivation of KBL could improve the production of 2,5-DMP. Besides 2,5-DMP, TMP can also be generated by Bacillus subtilis 168 by using l-threonine and d-glucose as the substrates and TDH as the catalytic enzyme.IMPORTANCE Despite alkylpyrazines' contribution to flavor and their commercial value, the synthesis mechanisms of alkylpyrazines by microorganisms remain poorly understood. This study revealed the substrate, intermediates, and related enzymes for the synthesis of 2,5-dimethylpyrazine (2,5-DMP), which differ from the previous reports about the synthesis of 2,3,5,6-tetramethylpyrazine (TTMP). The synthesis mechanism described here can also explain the production of 2,3,5-trimethylpyrazine (TMP). The results provide insights into an alkylpyrazine's synthesis pathway involving l-threonine-3-dehydrogenase as the catalytic enzyme and l-threonine as the substrate.

Characterization of Volatile Component Changes in Jujube Fruits during Cold Storage by Using Headspace-Gas Chromatography-Ion Mobility Spectrometry

Volatile components in jujube fruits from Zizyphus jujuba Mill. cv. Dongzao (DZ) and Zizyphus jujuba Mill. cv. Jinsixiaozao (JS) were analyzed under different cold storage periods via headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). Results identified 53 peaks that corresponded to 47 compounds and were mostly alcohols, aldehydes, esters, and ketones. Differences in the volatile components of jujube fruits were revealed in topographic plots and fingerprints. For DZ, 3-pentanone was the characteristic component of fresh fruits. After storage for 15 days, dipropyl disulfide became the most special substance. Moreover, when stored for 30 and 45 days, the fruits had some same volatile components, like 2-pentyl furan and diallyl sulfide. However, for DZ stored for 60 days, esters were the prominent constituent of the volatile components, simultaneously, some new alcohols appeared. For JS, 2-ethyl furan was the representative of fresh fruits, and 2-butoxyethanol content was the most abundant after 15 and 30 days of storage. Different from that in DZ, the content of ester in JS increased after storage for 45 days. Substances such as amyl acetate dimer, methyl salicylate, and linalool greatly contributed to the jujube flavor during the late storage period. Principal component analysis (PCA) showed that fresh samples and refrigerated fruits were effectively distinguished. Heat map clustering analysis displayed the similarity of volatile components in different samples and was in accordance with PCA results. Hence, the volatile components of jujube fruits can be readily identified via HS-GC-IMS, and jujube fruits can be classified at different periods based on the difference of volatile components.

Biological activities associated with the volatile compound 2,5-bis(1-methylethyl)-pyrazine

Pyrazines are 1,4-diazabenzene-based volatile organic compounds and known for their broad-spectrum antimicrobial activity. In the present study, we assessed the antimicrobial activity of 2,5-bis(1-methylethyl)-pyrazine, produced by Paenibacillus sp. AD87 during co-culture with Burkholderia sp. AD24. In addition, we were using transcriptional reporter assays in E. coli and mammalian cells to decipher the possible mode of action. Bacterial and mammalian luciferase reporter strains were deployed to elucidate antimicrobial and toxicological effects of 2,5-bis(1-methylethyl)-pyrazine. At high levels of exposure, 2,5-bis(1-methylethyl)-pyrazine exerted strong DNA damage response. At lower concentrations, cell-wall damage response was observed. The activity was corroborated by a general toxicity reporter assay in E. coli ΔampD, defective in peptidoglycan turnover. The maximum E. coli cell-wall stress activity was measured at a concentration close to the onset of the mammalian cytotoxicity, while other adverse outcome pathways, such as the activation of aryl hydrocarbon and estrogenic receptor, the p53 tumour suppressor and the oxidative stress-related Nrf2 transcription factor, were induced at elevated concentrations compared to the response of mammalian cells. Because of its broad-spectrum antimicrobial activity at lower concentrations and the relatively low mammalian toxicity, 2,5-bis(1-methylethyl)-pyrazine is a potential bio-based fumigant with possible applications in food industry, agriculture or logistics.

Identification of Dialkylpyrazines Off-Flavors in Oak Wood

Volatile extractive compounds from high-quality oak wood (Quercus sp.) are responsible for important pleasant olfactory notes, such as coconut, wood, vanilla, caramel, and spice. Recently, a new off-flavor reminiscent of rancid butter has been detected in oak wood. Using gas chromatography-olfactometry (GC-O) coupled to several detection modes, such as nitrogen-phosphorus detection (GC-O-NPD) or mass spectrometry (GC-O-MS) and multidimensional GC-O coupled to time-of-flight mass spectrometry, six compounds containing nitrogen atoms were identified. The volatiles were suggested to belong to 2,5-disubstituted pyrazines family, which was confirmed by comparison with synthetic reference compounds. For this purpose, symmetric and dissymmetric 2,5-dialkylpyrazines were prepared from methyl esters of corresponding aliphatic amino acids (Val, Leu, and Ile) by a three-step, one-pot reaction under mild reducing conditions. Organoleptic descriptors and odor detection thresholds were also determined, whereas a bacterial origin explaining these off-flavors was hypothesized.

Optimization of Headspace Solid-Phase Microextraction (HS-SPME) Parameters for the Analysis of Pyrazines in Yeast Extract via Gas Chromatography Mass Spectrometry (GC-MS)

Yeast extract was analyzed through headspace solid-phase microextraction (HS-SPME) in combination with (GC-MS) for its pyrazine compounds. Four different types of SPME fibers with various polarities were selected for preoptimization. The three coated fiber 50/30 µm DVB/CAR/PDMS showed the maximum volatile extraction efficiency and was selected for further analysis. Twenty-eight volatile compounds were tentatively identified through GC-MS including eight pyrazines and were categorically characterized as major volatile compounds responsible for the flavor enhancing notes in YE. Response surface methodology encoded with face centered central composite design was employed to optimize the experimental design. Average peak area of selected pyrazines; methylpyrazine, 2,3-dimethylpyrazine, 2,6-dimethylpyrazine, 2-ethyl-5-methylpyrazine, trimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine, tetramethylpyrazine, 3,5-diethyl-2-methylpyrazine, and 2,3,5-trimethyl-6-ethylpyrazine were optimized through RSM-CCD to get the best conditions for HS-SPME. The HS-SPME variables X₁ (equilibrium time), X₂ (extraction time), and X₃ (extraction temperature) were programed into the run sheets to opt an optimistic statistical approach. Among these, the variable X₂ and X₃ showed the most significant results with the response variable R and could be concluded as the most tantalize variables while practicing pyrazines extraction through HS-SPME method. Resultantly, the optimization methodology was successfully applied for the extraction of pyrazines from yeast extract. PRACTICAL APPLICATION: The selection of optimal conditions to conduct a HS-SPME experiment can dramatically affect the sensitivity and accuracy of aroma extraction process. Optimizing the SPME conditions is the best way to identify the role of all the possible factors that can fluctuate the volatile profile of any sample. This type of statistical approach to optimize the HS-SPME conditions for pyrazines in yeast extract was practiced for the very first time and could be considered as a prerequisite strategy to proliferate future projects related to some novel studies in terms of pyrazines flavor perception.

Alkylpyrazines from Coffee are Extensively Metabolized to Pyrazine Carboxylic Acids in the Human Body

SCOPE

Coffee is a complex mixture of over 1000 compounds, including diverse heteroaromatic compounds such as alkylpyrazines. Little is known about the intake, metabolism, and bodily distribution of these compounds. Therefore, a human intervention study is conducted to investigate the excretion of alkylpyrazine metabolites in urine after the ingestion of brewed coffee containing alkylpyrazines.

METHODS AND RESULTS

After consuming a diet without heat-processed food, ten volunteers consumed 500 mL of freshly brewed coffee prepared from coffee pads, providing intakes of 2-methylpyrazine (2-MeP), 2,5-dimethylpyrazine (2,5-DMeP), and 2,6-dimethylpyrazine (2,6-DMeP) amounting to 17.2, 4.4, and 4.9 µmol, respectively. These alkylpyrazines are metabolized into the corresponding pyrazine carboxylic acids, namely pyrazine-2-carboxylic acid (PA), 5-hydroxypyrazine-2-carboxylic acid (5-OHPA), 5-methylpyrazine-2-carboxylic acid (5-MePA), and 6-methylpyrazine-2-carboxylic acid (6-MePA). In total, 64% of the ingested 2-MeP is excreted as PA, as well as 26% as 5-OHPA, while 91% and 97% of the ingested 2,5-DMeP and 2,6-DMeP are recovered as 5-MePA and 6-MePA, respectively, in urine samples collected after coffee consumption.

CONCLUSION

This study provides evidence that alkylpyrazines are rapidly metabolized into the corresponding carboxylic acids and excreted via urine by humans, which is consistent with earlier rodent studies.

Mass spectrometry-based metabolomics of volatiles as a new tool for understanding aroma and flavour chemistry in processed food products

BACKGROUND

When foods are processed or cooked, many chemical reactions occur involving a wide range of metabolites including sugars, amino acids and lipids. These chemical processes often lead to the formation of volatile aroma compounds that can make food tastier or may introduce off-flavours. Metabolomics tools are only now being used to study the formation of these flavour compounds in order to understand better the beneficial and less beneficial aspects of food processing.

AIM OF REVIEW

To provide a critical overview of the diverse MS-based studies carried out in recent years in food metabolomics and to review some biochemical properties and flavour characteristics of the different groups of aroma-related metabolites. A description of volatiles from processed foods, and their relevant chemical and sensorial characteristics is provided. In addition, this review also summarizes the formation of the flavour compounds from their precursors, and the interconnections between Maillard reactions and the amino acid, lipid, and carbohydrate degradation pathways.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review provides new insights into processed ingredients and describes how metabolomics will help to enable us to produce, preserve, design and distribute higher-quality foods for health promotion and better flavour.

Determination of Antioxidant Capacity, Phenolics and Volatile Maillard Reaction Products in Rye-Buckwheat Biscuits Supplemented with 3β-d-Rutinoside

The Maillard reaction (MR) is responsible for the development of color, taste and aroma in bakery products though the formation of numerous aroma compounds such as pyrazines, pyrroles and aldehydes, nonvolatile taste active compounds and melanoidins. In this article, we investigate the effect of quercetin 3β-D-rutinoside (rutin) supplementation, at the level of 5⁻50 mg per 100 g, of rye-buckwheat biscuits on the formation of phenolics and volatile Maillard reaction products (MRPs) such as pyrazines, furfuryl alcohol and furfural, determined by headspace solid phase microextraction followed by gas chromatography⁻mass spectrometry (HS-SPME/GC⁻MS), in addition to the effect on the antioxidant capacity. The study confirmed that rutin was stable under baking conditions as showed by its content in rye-buckwheat biscuits. Supplementation of biscuits with increasing amounts of rutin resulted in the progressive increase of total phenolics and antioxidant capacity measured by DPPH and OxHLIA assays, but it had no effect on their sensory quality. From the eighteen compounds identified by HS-SPME/GC⁻MS in the volatile fraction of biscuits were quantitated as a compounds-of-interest: methylpyrazine, ethylpyrazine, 2,3-; 2,5- and 2,6-dimethylpyrazines, as well as furfural, furfuryl alcohol and hexanal. The rutin supplementation of biscuits might be one of the factors to influence the formation of both desirable volatile compounds and undesirable toxic compounds. In conclusion, this study indicates for the significant role of polyphenols on the formation of volatile compounds in biscuits with possible future application in the development of healthy bakery products with high antioxidant capacity.

Characterization of the Volatile Compounds in Raw and Roasted Georgia Pecans by HS-SPME-GC-MS

Volatile compounds are responsible for the characteristic aroma of raw and roasted pecans. Yet, much is unknown about the specific effects of roasting on pecan volatiles. In this study, the volatiles of raw "Desirable" pecans from Georgia and 3 roasted pecan samples (175 °C for 5, 10, and 15 min) were determined by HS-SPME coupled to GC-MS using stable deuterium-labeled volatiles as internal standards for quantitation. As expected, roasting markedly impacted the volatile profile of pecans: a total of 63 flavor-active compounds were identified in roasted samples, including 9 compounds not detected in raw "Desirable" pecans. Pyrazines, notable indicators of the Maillard reaction, were found only in roasted samples and demonstrated continual increases throughout observed roasting times. Furthermore, it was noted that hydrocarbon derivatives showed substantial increases with roasting, likely a result of the degradation of nonvolatile lipids. The observed changes correspond well to prior sensory investigations concerning the impact of roasting on pecan flavor, and explain increases in intensity for roasted, nutty, buttery, and sweet sensory traits. PRACTICAL APPLICATION: The results of this study document the volatile constituents generated during the roasting of pecans, and this may help formulators, who are trying to develop natural and artificial pecan flavors in new food products.

Nutty-like flavor production by Corynbacterium glutamicum 1220T from enzymatic soybean hydrolysate. Effect of encapsulation and storage on the nutty flavoring quality

The main objective of this study was to evaluate the ability of Corynbacterium glutamicum to produce a safe nutty like flavor from enzymatic soybean meal hydrolysate (E-SH) and to investigate the effect of encapsulation and storage on the quality of the produced nutty flavoring. C. glutamicum was incubated with E-SH, supplemented and un-supplemented with a mixture of threonine and lysine. The generated volatiles of each culture were subjected to odor sensory analysis. The volatile compounds were analyzed by headspace solid phase microextraction (HS-SPME) and gas chromatography coupled with mass spectrometry (GC-MS). The sample showed the best nutty aroma and highest content of the most odorant compounds of nutty flavor was subjected to toxicity test and encapsulated in Arabic gum using spray drier. The stability of the encapsulated flavoring was evaluated during storage. A high correlation was found between the culture growth and consumed sugars. The odor intensity of the generated nutty-chocolate like aroma showed a gradual increase during incubation time. Pyrazines and 2/3- methylbutanal showed the highest content at the end of fermentation time. Encapsulation gave rise to a significant decrease in the branched aldehydes, which are responsible for the chocolate note of the flavoring sample. The high odor intensity of the stored sample was correlated to the significant increase in the pyrazines. The results of GC-MS analysis confirmed those of odor sensory evaluation of the nutty-like flavor.

2-Alkyl-3-methoxypyrazines are potent attractants of florivorous scarabs (Melolonthidae, Cyclocephalini) associated with economically exploitable Neotropical palms (Arecaceae)

BACKGROUND

2-Alkyl-3-methoxypyrazines (MPs) are naturally occurring aromatic compounds involved in insect chemical communication as both pheromones and allelochemicals. Although rarely characterized in floral scents, they have been identified as major constituents in headspace samples from palm inflorescences and evidence pointed towards their function as attractive cues for scent-oriented pollinators, as well as florivores. In this study, we investigated the occurrence of MPs in economically exploitable palms belonging to Acrocomia and Attalea through headspace floral scent analysis and assessed their role in the selective attraction of flower-feeding cyclocephaline scarabs (Melolonthidae, Cyclocephalini) in field bioassays conducted in Brazil and Colombia.

RESULTS

Three different MPs were identified among floral headspace samples of Acrocomia aculeata, Acr. intumescens, Attalea butyracea and Att. insignis: 2-isopropyl-3-methoxypyrazine (IPMP), 2-isobutyl-3-methoxypyrazine (IBMP) and 2-(sec-butyl)-3-methoxypyrazine (SBMP). Their combined estimated total scent emissions per inflorescence ranged from 246 μg h-1 to 6.2 mg h-1 . Scented traps, individually baited with either IPMP or SBMP, resulted in species-selective and high yield captures of Cyclocephala amazona and C. distincta, known florivores associated with over 20 different species of Neotropical palms.

CONCLUSIONS

The identification of MPs as potent kairomones could prove instrumental in integrated pest management plans for these insects in emerging oil-yielding crops in South America, including those of the wine palm (Att. butyracea) and macaw palms (Acrocomia spp.). © 2018 Society of Chemical Industry.

Review on the Synthesis of Pyrazine and Its Derivatives

Pyrazine is a kind of natural product which can be found in plants, animals, insects, marine organisms andmicroorganisms. The main function of pyrazine in living organisms is used as flavor of the raw foods. Pyrazine and its derivatives were also produced in industries mainly for fragrance, flavor and pharmaceutical applications. This review describes the historical development of pyrazine including the discovery and synthesis, to the recent synthetic approach of pyrazinium. In general, six synthetic approaches namely condensation reaction, ring closure, metal catalysis, green reaction, Maillard reaction and acid catalyst on N-substitution have been reviewed in this paper. The first five approaches are mainly aimed for the substitution at 2, 3, 5 and 6 positions in pyrazine ring, whereas the last approach is specifically for 1 and 4 positions in pyrazine. Keywords: Diazine, pyrazine, and Maillard reaction

Replacing conventional decontamination of hatching eggs with a natural defense strategy based on antimicrobial, volatile pyrazines

The treatment of hatching eggs relies on classic yet environmentally harmful decontamination methods such as formaldehyde fumigation. We evaluated bacteria-derived volatiles as a replacement within a fundamentally novel approach based on volatile organic compounds (VOCs), which are naturally involved in microbial communication and antagonism due to their high antimicrobial efficiency. Pyrazine (5-isobutyl-2,3-dimethylpyrazine) was applied passively and actively in prototypes of a pre-industry-scale utilization. Altogether, pyrazine decontamination rates of up to 99.6% were observed, which is comparable to formaldehyde fumigation. While active evaporation was highly efficient in all experiments, passive treatment showed reducing effects in two of four tested groups only. These results were confirmed by visualization using LIVE/DEAD staining microscopy. The natural egg shell microbiome was characterized by an unexpected bacterial diversity of Pseudomonadales, Enterobacteriales, Sphingomonadales, Streptophyta, Burkholderiales, Actinomycetales, Xanthomonadales, Rhizobiales, Bacillales, Clostridiales, Lactobacillales, and Flavobacteriales members. Interestingly, we found that especially low pyrazine concentrations lead to a microbiome shift, which can be explained by varying antimicrobial effects on different microorganisms. Micrococcus spp., which are linked to embryonic death and reduced hatchability, was found to be highly sensitive to pyrazines. Taken together, pyrazine application was shown to be a promising, environmentally friendly alternative for fumigation treatments of hatchery eggs.

A Vibrio cholerae autoinducer-receptor pair that controls biofilm formation

Quorum sensing (QS) is a cell–cell communication process that enables bacteria to track cell population density and orchestrate collective behaviors. QS relies on production, detection, and response to extracellular signal molecules called autoinducers. In Vibrio cholerae, multiple QS circuits control pathogenesis and biofilm formation. Here, we identify and characterize a new QS autoinducer-receptor pair. The autoinducer is 3,5-dimethylpyrazin-2-ol, which we call DPO. DPO is made from threonine and alanine, and its synthesis depends on threonine dehydrogenase (Tdh). DPO binds to and activates a transcription factor, VqmA. The VqmA-DPO complex activates expression of vqmR, which encodes a small regulatory RNA. VqmR represses genes required for biofilm formation and toxin production. We propose that DPO allows V. cholerae to regulate collective behaviors to, among other possible roles, diversify its QS output during colonization of the human host.

Safety and efficacy of pyrazine derivatives including saturated ones belonging to chemical group 24 when used as flavourings for all animal species

Following a request from the European Commission, the EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of 22 compounds belonging to chemical group 24 (pyrazine derivatives). They are currently authorised as flavours in food. The FEEDAP Panel concludes that: 2,3-diethylpyrazine [14.005], 2-ethyl-3-methylpyrazine [14.006], 5,6,7,8-tetrahydroquinoxaline [14.015], 2,3,5,6-tetramethylpyrazine [14.018], 2,3,5-trimethylpyrazine [14.019], 2,5-dimethylpyrazine [14.020], 2,6-dimethylpyrazine [14.021], 2-ethylpyrazine [14.022], 2-ethyl-3,5-dimethylpyrazine [14.024], 2,5 or 6-methoxy-3-methylpyrazine [14.025], 2-methylpyrazine [14.027], acetylpyrazine [14.032], 6,7-dihydro-5-methyl-5H-cyclopenta(b)pyrazine [14.037], 2-isobutyl-3-methoxypyrazine [14.043], 2-acetyl-3-ethylpyrazine [14.049], 2,3-dimethylpyrazine [14.050], 2,3-diethyl-5-methylpyrazine [14.056], 2-(sec-butyl)-3-methoxypyrazine [14.062], 3,(5- or 6-)-dimethyl-2-ethylpyrazine [14.100], 2-ethyl-3-methoxypyrazine [14.112] and 2-methoxy-3-methylpyrazine [14.126] are safe at the proposed maximum dose level (0.5 mg/kg complete feed) as feed for cattle, salmonids and non-food-producing animals, and at the proposed normal use level of 0.1 mg/kg complete feed for pigs and poultry; 5-methylquinoxaline [14.028] are safe only at concentrations below the proposed use levels (0.08 mg/kg complete feed for cattle, salmonids and non-food-producing animals, and 0.05 mg/kg complete feed for pigs and poultry). No safety concern would arise for the consumer from the use of these compounds up to the highest proposed level in feeds. Hazards for skin and eye contact, and respiratory exposure are recognised for the majority of the compounds under application. Most are classified as irritating to the respiratory system. The proposed maximum use levels in feed are unlikely to have detrimental effects on the terrestrial and fresh water compartments. Because all the compounds under assessment are used in food as flavourings and their function in feed is essentially the same as that in food, no further demonstration of efficacy is necessary.

Investigating a persistent odor at an aircraft seat manufacturer

An aircraft seat manufacturing company requested a NIOSH health hazard evaluation to help identify a strong odor that had persisted throughout the facility for over a year. Employees reported experiencing health effects thought to be related to the odor. We collected and analyzed area air samples for volatile organic compounds, endotoxin, bacterial and fungal metagenome, and metalworking fluid aerosol. Bulk metalworking fluid samples were analyzed for endotoxin, bacterial and fungal metagenome, and viable bacteria and fungus. We also evaluated the building ventilation systems and water diversion systems. Employees underwent confidential medical interviews about work practices, medical history, and health concerns. Based on our analyses, the odor was likely 2-methoxy-3,5-dimethylpyrazine. This pyrazine was found in air samples across the facility and originated from bacteria in the metalworking fluid. We did not identify bacteria known to produce the compound but bacteria from the same Proteobacteria order were found as well as bacteria from orders known to produce other pyrazines. Chemical and biological contaminants and odors could have contributed to health symptoms reported by employees, but it is likely that the symptoms were caused by several factors. We provided several recommendations to eliminate the odor including washing and disinfecting the metalworking machines and metalworking fluid recycling equipment, discarding all used metalworking fluid, instituting a metalworking fluid maintenance program at the site, and physically isolating the metalworking department from other departments.

Effect of cooking on aroma profile of red kidney beans (Phaseolus vulgaris) and correlation with sensory quality

Volatile aroma compounds of three varieties of red kidney beans (Phaseolus vulgaris) namely Kashmiri red, Sharmili and Chitra were extracted in raw state using solid-phase microextraction (SPME) and cooked state using simultaneous distillation extraction (SDE). During cooking a significant (p<0.05) reduction in the content of several aldehydes, alcohols and terpene hydrocarbons while an increase in content of various sulfurous compounds, terpene alcohols, ketones and pyrazines was noted. Descriptive sensory analysis showed that the maximum intensity of 'kidney bean', 'earthy' and 'smoky' odour was observed in Kashmiri red while Sharmili variety was characterised by 'sulfurous' odour. Correlation of volatile profile data with descriptive sensory analysis and odour activity values clearly established the role of compounds, such as methanethiol, diethyl sulfide, dimethyl disulfide, methional and dimethyl trisulfide, in contributing to 'cooked kidney bean' aroma, while dimethyl sulfoxide, dimethyl sulfone and ethyl methyl sulfone were responsible for 'sulfurous' aroma.