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Flavor is one of the most important characteristics of chocolate products and is due to a complex volatile fraction, depending both on the cocoa bean genotype and the several processes occurring during chocolate production (fermentation, drying, roasting and conching). Alkylpyrazines are among the most studied volatiles, being one of the main classes of odorant compounds in cocoa products. In this work, a mass spectrometric approach was used for the comparison of cocoa liquors from different countries. A headspace solid-phase microextraction gas chromatography-mass spectrometry method was developed for the qualitative study of the volatile fraction; the standard addition method was then used for the quantitative determination of five pyrazines (2-methylpyrazine, 2,3-dimethylpyrazine, 2,5-dimethylpyrazine, 2,3,5-trimethylpyrazine and tetramethylpyrazine). Satisfactory figures of merit were obtained: Limits of quantitation were in the range 0.1-2.7?ng/g; repeatability and reproducibility varied between 3% and 7% and between 8% and 14%, respectively. The total content of the pyrazines was remarkably different in the considered samples, ranging from 99 to 708?ng/g. Tetramethylpyrazine showed the highest concentration in all samples, with a maximum value of 585?ng/g. A preliminary study was also performed on the nonvolatile fraction using LC-MS/MS, identifying some flavanols such as catechin, epicatechin and procyanidins. Copyright ? 2012 John Wiley & Sons, Ltd. 相似文献
403.
404.
Emanuele F. Pissinati José A. C. Delgado Pedro A. M. Moro Dr. José T. M. Correia Prof. Dr. Roberto G. S. Berlinck Prof. Dr. Márcio W. Paixão 《European journal of organic chemistry》2023,26(21):e202300274
A site-selective carbamoylation strategy to access non-proteinogenic N4-modified asparagines has been described. The protocol is characterized by mild reaction conditions, high functional group compatibility, and a wide diversity of functionalized carbamoyl radicals making possible the access to peptides, pharmaceuticals, and natural N4-asparagine conjugates, as well as enantioenriched unnatural N4-asparagines. Besides that, deuterated analogues were achieved with the insertion of D2O and enantioenriched derivatives could be obtained in 15 min in continuous-flow conditions. 相似文献
405.
Fabio Ganazzoli Giuseppe Allegra Emanuele Colombo Mario De Vitis 《Macromolecular theory and simulations》1992,1(5):299-310
The configurational, or elastic, free energy Ael of a polymer chain is discussed in terms of the Fourier configurational approach. The importance of accounting for all degrees of freedom of the chain is shown in comparison with affine mean-field theories and with scaling theories of chain expansion and contraction. In case of strong contraction the chain does show neither affinity nor self-similarity, and we get Ael ∼ N1/3, N being the number of chain bonds. Conversely, in case of good-solvent expansion we find Ael ∼ N. The same result holds in the vicinity of the Θ-temperature, where Ael is also proportional to [(T − Θ)/T]2. 相似文献