• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4271-4274
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• 2012

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.1939-1945
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• 2009

Kinetic investigations on the oxidation of pyrazine and four 2-substituted pyrazines viz., 2-methylpyrazine, 2-ethylpyrazine, 2-methoxypyrazine and 2-aminopyrazine by bromamine-B (BAB) to the respective N-oxides have been studied in HCl$O_4$ medium at 303 K. The reactions show identical kinetics being first-order each in $[BAB]_o\;and\;[pyrazine]_o$, and a fractional- order dependence on $[H^+]$. Effect of ionic strength of the medium and addition of benzenesulfonamide or halide ions showed no significant effect on the reaction rate. The dielectric effect is positive. The solvent isotope effect was studied using $D_2$O. The reaction has been studied at different temperatures and activation parameters for the composite reaction have been evaluated from the Arrhenius plots. The reaction showed 1:1 stoichiometry and the oxidation products of pyrazines were characterized as their respective N-oxides. Under comparable experimental conditions, the oxidation rate of pyrazines increased in the order: 2-aminopyrazine > 2-methoxypyrazine > 2-ethylpyrazine > 2-methylpyrazine > pyrazine. The rates correlate with the Hammett $\sigma$ relationship and the reaction constant $\rho$ was found to be -0.8, indicating that electron donating centres enhance the rate of reaction. An isokinetic temperature of $\beta$ = 333 K, indicated that the reaction was enthalpy controlled. A mechanism consistent with the experimental results has been proposed in which the rate determining step is the formation of an intermediate complex between the substrate and the diprotonated species of the oxidant. The related rate law in consistent with observed results has been deduced.

• Preventive Nutrition and Food Science
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• v.2 no.4
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• pp.360-367
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• 1997

The chemistry background of the Maillard reaction focused on pyrazines and factors affecting the reaction products were reviewed. The Maillard reaction, also called a non-enzymatic browning reaction, is quite complex and generates numerous reaction products. In processed foods, it is generally accepted as a key reaction to produce flavor components. Specially, pyrazines possess an important impact character on the roasted foods with other heterocyclic compounds. The Maillard reaction is initiated by condensation between reducing sugar and amino group, and N-glycosylamines are produced via Schiff base with dehydration of water. After the rearrangement of the N-glycosylamines, they follow transformation into deoxyhexosones which are reactive intermediates. Degradation and fragmentation are facilitated by rearranged compounds. By condensation, pyrazine, one of the final Maillard products, is generated as a relatively stable form to provide specific aromas. During the processes of the reaction, chemical or physical environmental parameters affect the formation of the products.

• Korean journal of food and cookery science
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• v.20 no.3
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• pp.265-270
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• 2004

To investigate the formation of pyrazines, by-products of chicken were hydrolyzed by protease/peptidase for 4, 8 and 24 hours, after which the hydrolysates were heated with glucose, fructose and xylose, respectively, at l80$^{\circ}C$ for l00min. The formation of pyrazines showed a significant difference by quality and quantity according to the degree of protein hydrolysis. Especially, the formation of 2-methyl pyrazine and 2-ethyl-5-methyl pyrazine was considerably affected by, the degree of protein hydrolysis. Also, 3-ethyl-5-methyl pyrazine, 2-butyl-3-methyl pyrazine, 2-butyl-3,5-dimethyl pyrazine, methyl pyrazine, and 3-ethyl-5-methyl pyrazine were identified only in the hydrolysates for 24 hours.

• Food Science and Biotechnology
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• v.18 no.3
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• pp.700-705
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• 2009

In this study, the volatile compounds in 9 commercial fermented soybean pastes were extracted and analyzed by headspace-solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS), respectively. A total of 63 volatile components, including 21 esters, 7 alcohols, 7 acids, 8 pyrazines, 5 volatile phenols, 3 ketones, 6 aldehydes, and 6 miscellaneous compounds, were identified. Esters, acids, and pyrazines were the largest groups among the quantified volatiles. About 50% of the total quantified volatile material was contributed by 5 compounds in 9 soybean paste samples; ethyl hexadecanoate, acetic acid, butanoic acid, 2/3-methyl butanoic acid, and tetramethyl-pyrazine. Three samples (CJW, SIN, and HAE) made by Aspergillus oryzae inoculation showed similar volatile patterns as shown in principal component analyses to GC-MS data sets, which showed higher levels in ethyl esters and 2-methoxy-4-vinylphenol. Traditional fermented soybean pastes showed overall higher levels in pyrazines and acids contents.

• Korean Journal of Food Science and Technology
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• v.32 no.3
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• pp.654-658
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• 2000

Flavor components focused on the methyl pyrazines(2,3-dimethyl pyrazine, 2,3,5-trimethyl pyrazine, tetramethyl pyrazine) of microwave-roasted cocoa beans were determined and compared with those of conventionally-roasted cocoa beans. Domestic microwave oven was modified to design the microwave roasting system. Temperature measurement technique using thermocouple probes was developed to determine the center temperature of cocoa beans during microwave roasting. Microwave roasting was carried out under two different conditions. Under the first condition, roasting time was fixed to 30 min, while roasting temperature was varied to $110^{\circ}C,\;120^{\circ}C,\;130^{\circ}C,\;140^{\circ}C,\;and\;150^{\circ}C$ Under the second condition, roasting temperature was fixed to $130^{\circ}C$, while roasting time was varied to 5 min, 10 min, 20 min, and 30 min. Conventional roasting was done at $120^{\circ}C$ for 15 min as a reference. Amount of methyl pyrazines and their ratios were influenced by microwave roasting temperature and roasting time. The most suitable methyl pyrazine ratio of cocoa beans was obtained at $140^{\circ}C$ for 30 min of microwave roasting.

• Preventive Nutrition and Food Science
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• v.4 no.2
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• pp.88-91
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• 1999

Aroma components of tea processed from Korean chicory roots were isolated and identified. The model system of amino-carbonyl reaction was carried out to study the formation mechanism of aroma compounds of chicory tea during manufacturing process. The concentration extracts from chicory tea and model system were analyzed and identified by gas chromatography(GC) and GC-mass spectrometry. Twenty-nine compounds, including pyrazines, furans, acids, alcohols, pyrroles and lactones were isolated and identified in chicory tea. The main compounds were pyrazines including methyl pyrazine, 2,5-dimethyl pyrazine, 2, 6-dimethyl pyrazine, 2-ethyl-6-methyl pyrazine, 2-ethyl-3-methyl pyrazine, thrimethyl pyrazine, 3-ethyl-2-5-dimenthyl pyrazine, 5-ethyl-2-3-dimenthyl pyrazine, and 2-acetyl-3-methy pyrazine and pyrroles including acethl pyrrole and formlyl pyrrole ; and furans including furfural , acetyl furan, 5-methyl furan, 5-methyl furfuralm, and furfuryl alcohol. These pyrazine compounds of a roasted and nutty aroma may be important contributors to the flavor of chicory tea. The aroma concentrate of model system also had a roasted and nutty aroma and the main compounds were methyl pyrazine, 2, 5-dimetyl pyrazine, 2, 6-dimethyl pyrazine and trimethyl pyrazine.

• Proceedings of the EASDL Conference
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• 2004.10a
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• pp.107-129
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• 2004

Sesame oil has been popular for hundreds of years in Korea because of its pleasant flavor and health benefits and has been studied for its antioxidant properties and flavor preferences attributed to its manufacturing methods. The objective of this study was to investigate the qualitative properties of six commercial sesame oils (3 Korean, 2 Japanese, 1 Chinese), The fatty acids in the oil are composed of two main acids oleic acid and linoleic acid with a P/S ratio of 4.99${\sim}$5.73. Of the tocopherol isomers, ${\gamma}$-toc ranged from 23.14 to 34.85mg/100g. Lignan such as sesamin(322.91${\sim}$689.39ppm) and sesamolin (62.19${\sim}$289.82 ppm) is found predominantly in sesame oil. Sesamol (8.52${\sim}$51.21 ppm) was significantly different depending on manufacturer, observed as greatest in the Korean and least in the Japanese products. The induction period was longest in order of the Korean, Chinese, and then Japanese product. The red and yellow values in Lovibond color were highest in the Korean and lowest in the Japanese product. The major volatile compounds (in order of content) were pyrazines, phenols, aldehydes, and then furans and contained a small amount of pyrroles, thiazoles and indoles. The levels of total volatiles were greatest in the Korean and least in the Japanese product. The most abundant volatiles in the Korean product were pyrazines, whereas phenols were higher in the Chinese product compared to the others. From these results, the relationships among pyrazines, sesamol, yellowness and induction period showed positive, respectively. In sensory evaluation, Korean panelists preferred, in order, the Korean, Japanese, and then the Chinese product in strength of and preference for the sesame flavor, also ranking it best in overall acceptance. Japanese panelists found similarities in the Korean and Japanese products and gave an equal level of preference for the sesame flavor and overall acceptance. On the other hand, Chinese panelists preferred the Japanese product in strength and sesame flavor rating it best on overall acceptance.

• Food Science and Biotechnology
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• v.18 no.6
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• pp.1495-1499
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• 2009

The volatiles formed from the reactions of L-ascorbic acid with L-alanine at 5 different pH (5, 6, 7, 8, or 9) and $140{\pm}2^{\circ}C$ for 2 hr was performed using solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) analysis were identified to be 25 different kinds. The reaction between L-ascorbic acid and L-alanine led mainly to the formation of pyrazines. Many of these were alkylpyrazines, such as 3-ethyl-2,5-dimethylpyrazine, 2,5-dimethylpyrazine, 2-ethyl-5-methylpyrazine, 3,5-diethyl-2-methylpyrazine, methylpyrazine, 2-ethyl-6-methylpyrazine, and 2,3-diethyl-5-methylpyrazine, other compounds identified were furans, phenols, benzoquinones, 2,4,6-trimethylpyridine, and 2-methylbenzoxazole. The studies showed that furans, such as furfural and benzofuran were formed mainly at acidic pH. In contrast, higher pH values could promote the production of pyrazines.

• Fibers and Polymers
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• v.1 no.2
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• pp.71-75
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• 2000

Intermolecular cyclization of 2-alkylamino-3-chloro-5,6-dicyanopyrazine 2 in the presence of tributylamine in N,N-dimethylformamide (DMF) gave 5,10-disubstituted-2,3,7,8-tetracyano -5,10-dihydrodipyrazino〔2,3-b:2',3'-e]pyrazines 3, which showed strong mesomorphic property and were anticipated as new chromophoric system for functional dye materials. Absorption spectra, fluorescent properties and other physical properties were correlated with their chemical structures. Vanadyl oligomeric porphyrazine with long alkyl groups synthesized from 3 had satisfactory solubility in tetrahydrofuran (THF), diethyl ether and dimethylsulfoxide (DMSO). The syntheses and characterization of vanadyl polymeric porphyrazines derived from 3 with long alkyl groups are reported.