Characterization of cocoa liquors by GC-MS and LC-MS/MS: focus on alkylpyrazines and flavanols

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.     

Expanding the Chemical Space of Non-Proteinogenic N4-Substituted Asparagine: Racemic,Enantioenriched, and Deuterated Derivatives

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.