Ultrahigh Performance Liquid Chromatography Analysis of Volatile Carbonyl Compounds in Virgin Olive Oils

The enzymatic and chemical oxidation reaction in olive oil produces many volatile carbonyl compounds that contribute to the complex flavor of olive oil. A novel ultrahigh performance liquid chromatography (UHPLC) method with dynamic headspace sampling and 2,4-dinitrophenylhydrazine (DNPH) derivatization were established to determine the volatile carbonyls in virgin olive oil. Quantification of nine characteristic carbonyls (acetone, hexanal, <i>E</i>-2-hexenal, octanal, <i>E</i>-2-octenal, nonanal, <i>E</i>-2-nonenal, <i>E</i>,<i>E</i>-2,4-nonadienal, and <i>E</i>,<i>E</i>-2,4-decadienal) was achieved using cyclopentanal as an internal standard. This method provides comparable linearity (<i>R</i>² = 0.9917–1.0000) and repeatability (less than 7.6% relative standard deviations) with solid phase microextraction gas chromatography (SPME-GC). The relative standard deviations (%RSD) of all applied carbonyl standards were lower than 7.6%. The limits of detection (LOD) and quantification (LOQ) were in the ranges of 1.6–150.1 and 4.8–906.1 μg/kg. The recoveries obtained for olive oil samples were in the range of 81.0–115.3%. To show the potential of this method on the quantification of other volatile carbonyls that were not included in this study, GC–electron ionization mass spectrometry (GC–EI/MS) was employed to identify the derivatized carbonyls (carbonyl (2,4-DNPH) hydrazones) while peak assignments were made on the basis of elution sequences and peak areas. This method provided feasibility of using LC to determine volatile carbonyls in oil matrices, which can be applied to exam the degree of lipid oxidation and evaluate the sensory properties of VOO and other edible oils

Biosynthesis and Conformational Properties of the Irregular Sesquiterpenoids Isothapsadiene and β‑Isothapsenol

A carbocation cyclization/rearrangement mechanism for the biosynthesis of isothapsadiene and β-isothapsenol is shown to be energetically viable on the basis of density functional theory (DFT) calculations. In addition, for both isothapsadiene and β-isothapsenol, variable-temperature NMR experiments reveal two equilibrium conformers that undergo hindered exchange. The identities of these conformers, which are related by a chair-flip, are confirmed by DFT calculations on their structures, energies, ¹H and ¹³C chemical shifts, and interconversion pathways

Biosynthesis and Conformational Properties of the Irregular Sesquiterpenoids Isothapsadiene and β‑Isothapsenol

A carbocation cyclization/rearrangement mechanism for the biosynthesis of isothapsadiene and β-isothapsenol is shown to be energetically viable on the basis of density functional theory (DFT) calculations. In addition, for both isothapsadiene and β-isothapsenol, variable-temperature NMR experiments reveal two equilibrium conformers that undergo hindered exchange. The identities of these conformers, which are related by a chair-flip, are confirmed by DFT calculations on their structures, energies, ¹H and ¹³C chemical shifts, and interconversion pathways

Biosynthesis and Conformational Properties of the Irregular Sesquiterpenoids Isothapsadiene and β‑Isothapsenol

A carbocation cyclization/rearrangement mechanism for the biosynthesis of isothapsadiene and β-isothapsenol is shown to be energetically viable on the basis of density functional theory (DFT) calculations. In addition, for both isothapsadiene and β-isothapsenol, variable-temperature NMR experiments reveal two equilibrium conformers that undergo hindered exchange. The identities of these conformers, which are related by a chair-flip, are confirmed by DFT calculations on their structures, energies, ¹H and ¹³C chemical shifts, and interconversion pathways