Elucidation of Dimethylalkylpyrazines from the Ant Streblognathus aethiopicus by GC-FTIR

The presumed mandibular gland secretions from the workers and gamergates of two colonies of Streblognathus aethiopicus have been found to contain a homologous series of 3,5-dimethyl-2-alkylpyrazines (3,5-dimethyl-2-butylpyrazine, 1; 3,5-dimethyl-2-pentylpyrazine, 2; and 3,5-dimethyl-2-hexylpyrazine, 3). The structures of these compounds were determined from their mass spectra along with a comparison of their GC-FTIR spectra with those of all the isomers of a lower homolog. This is the first time that this combination of techniques has been applied to the study of insect pyrazines. The relative amounts and proportions of these compounds were different for gamergates and workers, with the latter containing 2–10 times more total pyrazines and having a higher proportion of 2 and 3. The possible significance of this finding is discussed.     

Matrix effects on flavour volatiles release in dark chocolates varying in particle size distribution and fat content using GC–mass spectrometry and GC–olfactometry

Influences of matrix particle size distribution (PSD) (18, 25, 35 and 50 μm) and fat content (25%, 30% and 35%) on flavour release of dark chocolate volatiles were quantified by static headspace gas chromatography using GC–MS. Sixty-eight (68) flavour compounds were identified, comprising alcohols, aldehydes, esters, ketones, furans, pyrans, pyrazines, pyridines, pyroles, phenols, pyrones and thiozoles. From GC–olfactometry, 2-methylpropanal, 2-methylbutanal and 3-methylbutanal had chocolate notes. With cocoa/roasted/nutty notes were trimethyl-, tetramethyl-, 2,3-dimethyl-, 2,5-dimethyl-, 3(or 2),5-dimethyl-2(or 3)-ethyl- and 3,5(or 6)-diethyl-2-methylpyrazine and furfuralpyrrole. Compounds with fruity/floral notes included 3,7-dimethyl-1,6-octadien-3-ol and 5-ethenyltetrahydro-R,R,5-trimethyl-cis-2-furanmethanol. Caramel-like, sweet and honey notes were conferred by 2-phenylethanol, phenylacetaldehyde, 2-phenylethylacetate, 2,3,5-trimethyl-6-ethylpyrazine, 2-carboxaldehyde-1H-pyrrole, furancarboxaldehyde, furfuryl alcohol and 2,5-dimethyl-4-hydroxy-3(2H)furanone. There were direct relationships of fat content with 3-methylbutanal and branched pyrazines but inverse ones with 2-phenylethanol, furfuryl alcohol, methylpyrazine, phenylacetaldehyde, 2, 3, 5-trimethyl-6-ethylpyrazine and 2-carboxaldehyde-1-H-pyrrole. Particle size influenced higher alcohol, aldehyde, ester, ketone and pyrazine concentrations at all fat contents. A multivariate product space suggested flavour effects of the interacting factors.     

Effects of enzymatic modification of wheat protein on the formation of pyrazines and other volatile components in the Maillard reaction

Enzymatically hydrolysed wheat gluten hydrolysate (WGH) was deamidated using glutaminase to produce deamidated wheat gluten hydrolysate (DWGH). Volatile components were analysed in WGH and DWGH thermally reacted with glucose or fructose. In the reaction system containing glucose, 19 pyrazines, 2 furans, and 5 sulphur-containing components were detected in WGH, while 34 pyrazines, 4 furans, and 7 sulphur-containing components were found in DWGH. In the system containing fructose, 24 pyrazines, 3 furans, and 6 sulphur-containing components were identified in the thermal reaction of WGH, whereas 36 pyrazines, 4 furans, and 8 sulphur-containing components were found in DWGH. The volatile components increased in DWGH, both qualitatively and quantitatively, mainly due to free ammonia released by deamidation. More volatiles were also developed in WGH and DWGH with fructose than with glucose. It was found that ammonia released from wheat protein via deamidation participated in the generation of diverse volatile components including pyrazines in the Maillard reaction.     

Identification of pyrazine derivatives in a typical maple syrup using headspace solid-phase microextraction with gas chromatography–mass spectrometry

Headspace solid-phase microextraction combined with gas chromatography–mass spectrometry was applied to identify pyrazines in a typical maple syrup characterised by plant ligneous or sawdust flavour. Carboxen/polydimethylsiloxane (85 μm) fibre and Supelcowax 10 column were selected instead of Carbowax/divinylbenzene (65 μm) fibre and VF-5ms column, respectively, because of their high capacity to extract and separate pyrazines. A total of 27 pyrazines were identified. To our knowledge, about half of these compounds had not previously been detected in maple syrup and 15 pyrazines were flavour components.     

Effect of Reaction Conditions on the Volatile Pyrazines Components of Defatted Flaxseed Meal in the Maillard Reaction System

Defatted flaxseed meal, as a high-protein by-product can be used as a good raw material for the Maillard reaction (MR). A MR model system was established using glucose, fructose, and glucose/fructose (1:1) to produce volatile compounds typically obtained from defatted flaxseed meal protein hydrolysate; these compounds were analyzed using head-space solid phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC–MS). From the 12 MR model reaction groups, the production of pyrazines was between 12.76% and 26.56%. In the 1G group (the group prepared using DH₁ = 7.87% with a glucose concentration of 10%), the amount of pyrazines generated reached 26.56%, and this was higher than that of the other 11 model reaction groups. The effect of reaction temperature (100–150 °C), reaction time (10–60 min), and sugar concentration (5–30%) on pyrazine content was determined using the 1G group. The results of this study indicated that the effect of temperature on pyrazine production was higher than that exerted by reaction time and glucose addition. The pyrazine content reached the maximum at a reaction temperature of 140 °C. The degree of reaction and pH value were also determined; the results demonstrated that accumulation of pyrazines was suboptimal when the pH of the system was dramatically decreased. For the overall reaction, the pyrazine content remained similar to that of the final products; however, the pyrazine content exhibited little correlation with the intermediate products in the MR.     

Pyrazines as marking volatiles in philanthine and nyssonine wasps (Hymenoptera: Sphecidae)

Males of several sphecid wasps apply volatile secretion on specific sites, perches. The odor is supposed to act in premating behavior as an attracting pheromone. There are strong indications that the scenting material is produced by the mandibular glands. One philanthine species,Philanthus triangulum, and three nyssonine ones,Argogorytes fargei, A. mystaceus, andNysson spinosus, the latter cleptoparasite onArgogorytes wasps, have been analyzed by gas chromatography-mass spectrometry. The major compound in the mandibular gland secretion of the four species was tentatively identified as 2,5-dimethyl-3-isopentylpyrazine. A few other pyrazines not yet identified were also found. Preliminary tests withP. triangulum show that alkylpyrazines influence male behavior.     

Pyrazines in extruded malt

Green malt, partially dried, was processed by high-temperature short-time (HTST) extrusion cooking at three different temperatures. Volatile components of the product were analysed by gas chromatography (g.c.) using a headspace sampling technique, and identified by mass spectrometry (m.s.). The concentration of pyrazines increased when the temperature was increased from 130 to 160°C, but it fell at 190°C, probably as an effect of volatilisation. However, the influence of parameters such as water content, the milling of the raw material and its residence time in the extruder must also be taken into account. Extruded malt contained more total pyrazines than conventionally processed malt. 2-Vinyl-5-methylpyrazine and 2-vinyl-6-methylpyrazine were found only in extruded malt, especially at high processing temperature. The pyrazine content per colour unit was high, an observation which may lead to the production of a more flavourful beer of the lager-type.     

Formation of pyrazines in hydroxyacetaldehyde and glycine nonenzymatic browning Maillard reaction: A computational study

By considering the formation of pyrazines (C₄N₂H₆ and C₄N₂H₄) as one of the possible final Maillard flavour compounds, Density Functional Theory computations at the standard state have been performed on the proposed mechanisms of glyoxal and glycine in the advanced stage of hydroxyacetaldehyde and glycine nonenzymatic browning reaction under different pH conditions. The results reveal that the basic condition is the most favourable for the production of pyrazines (Pzs), and the aqueous solution is more favourable than that of the gaseous state. The reactions at the isoelectric point of glycine and under neutral conditions are the second and third most favourable for the production of Pzs, respectively. The reaction under acidic conditions is the least feasible for the production of Pzs. Amino acetaldehyde is the most likely precursor of the pyrazine ring in the reaction. Presence of air or oxygen is necessary for the production of 2,3,5,6-tetrahydropyrazine (C₄N₂H₄) from 3,6-dihydropyrazine (C₄N₂H₆). Water is necessary with glyoxal and glycine species for the formation of Pzs and water is produced as a by-product during the formation of Pzs.     

Release of Five Indicator Volatiles from a Model Meat Emulsion to Study Phase Contribution to Meat Aroma

The objective of this work was to develop a model meat emulsion in order to study the release of aroma-related compounds from the lipid and aqueous phases. Hexanal, octanal and nonanal were taken as indicators of lipid oxidation whereas 2-ethyl-3,5-dimethyl pyrazine and 2-methyl pyrazine were Maillard reaction indicators. Four systems were studied: I) a model meat emulsion; II) phosphate buffer; III) phosphate buffer + myofibrillar proteins; and IV) canola oil. Release of indicator compounds from each of the studied systems was analyzed in the headspace. It was concluded that pyrazines mainly contributed to aroma in lipid systems and in protein solutions but not in emulsions and non protein aqueous systems. Hexanal, octanal, and nonanal were minor aroma contributors in lipid media, whereas hexanal and nonanal were released in small amount from protein emulsions. Conversely, octanal can be considered of an important aroma contributor in emulsions; the three aldehydes showed a high release from aqueous systems, with and without protein.