Isothermal Kováts retention indices of sulfur compounds on a poly(5% diphenyl-95% dimethylsiloxane) stationary phase

Comparison of Odorants in Beef and Chicken Broth-Focus on Thiazoles and Thiazolines

The shift in consumer landscape towards vegan, vegetarian and flexitarian diets has created an unprecedented challenge in creating meat aroma from plant-based alternatives. The search for potential vegan solutions has thus led to a renewed interest in authentic meat flavour profiles. To gain a better understanding of the qualitative odour differences between boiled beef and boiled chicken, aroma extracts were isolated using Likens-Nickerson simultaneous distillation-extraction (SDE), selected expressly because the in-situ heating of the sample facilitates the capture of aroma intermediates during the cooking process, thereby mimicking the cooking of meat in stocks and stews. The extracts were then analysed by Gas Chromatography-Mass Spectrometry (GC-MS) and GC-Olfactometry (GC-O). Most of the volatiles identified in this study were sulfur-containing compounds, such as sulfides, thiols, mercaptoaldehydes and mercaptoketones, which are derived from the Maillard reaction. Meanwhile, lipid oxidation results in the formation of unsaturated aldehydes, such as alkenals and alkadienals. Families of thiazoles and 3-thiazolines were found in the extracts. Two novel 3-thiazolines (5-ethyl-2,4-dimethyl-3-thiazoline and 2-ethyl-4,5-dimethyl-3-thiazoline) which may also contribute to the meaty aroma were identified in this work and synthesised from their respective aldehyde and mercaptoketone precursors.

Studies on volatile organic compounds of some truffles and false truffles

Results of solid phase micro-extraction coupled to gas chromatography and mass spectrometry analyses, accomplished on sporophores of 11 species of truffles and false truffles, are reported. Volatile organic compounds (VOCs) found in Gautieria morchelliformis were dimethyl sulphide, 1,3-octadiene, 3,7-dimethyl-1,6-octadien-3-ol, amorphadiene, isoledene and cis-muurola-3,5-diene. In Hymenogaster luteus var. luteus, presence of 1,3-octadiene, 1-octen-3-ol, 3-octanone, 3-octanol and 4-acetylanisole was revealed. Two VOCs, 4-acetylanisole and β-farnesene, constituted aroma of Hymenogaster olivaceus.Melanogaster broomeanus exhibited as components of its aroma 2-methyl-1,3-butadiene, 2-methylpropanal, 2-methylpropanol, isobutyl acetate, 3,7-dimethyl-1,6-octadien-3-ol, 3-octanone and β-curcumene. VOC profile of Octavianina asterosperma was characterised by the presence of dimethyl sulphide, ethyl 2-methylpropanoate, methyl 2-methylbutanoate and 3-octanone. Tuber rufum var. rufum and Pachyphloeus conglomeratus showed the presence of dimethyl sulphide only.

Chemical constituents and antimicrobial activities of the essential oils from Sedum pallidum var. bithynicum and S. spurium grown in Turkey

Chemical compositions of the essential oil of Sedum pallidum Bieb. var. bithynicum (Boiss.) and S. spurium Bieb. (Crassulaceae) from Turkey were investigated by GC-MS, and antimicrobial activity of the oil samples were assessed against Gram-positive/negative bacteria and yeast-like fungi. Thirty-eight and thirty-five components were identified in the essential oils and the main components of these species were found to be caryophyllene oxide from S. pallidum var. bithynicum and hexahydrofarnesyl acetone from S. spurium in the ratios of 12.8% and 15.7%, respectively. The isolated essential oils of the plants showed low antimicrobial activity against Gram-negative/positive bacteria and yeast-like fungi, having the MIC values of 500-2000 microg/mL. Antibacterial activity was not observed against Bacillus cereus.

Temperature dependence of the Kováts retention index. Convex or concave curves

The non-linearity in the temperature dependence of the Kováts index, I (the formation of convex or concave curves) was characterized by the second derivative, d2I/dT2. The expression deduced on a purely mathematical-physicochemical basis is d2I/dT2 = [2TDeltaS(CH2)dI/dT-100deltaDeltaCp]/TDeltaG(CH2). The solute-dependent factor for dI/dT, d2I/dT2, and the extreme temperature in the I vs. T relationship is deltaDeltaCp, which is the molar solvation heat capacity difference between the solute and a hypothetical n-alkane which elutes at the same time as the given solute, while the solvent-dependent factors are the solvation entropy and free energy of the methylene unit, DeltaS(CH2) and DeltaG(CH2). Experimentally, convex Ivs.T curves with a minimum are formed when deltaDeltaCp >> 0, while concave ones with a maximum are observed when deltaDeltaCp << 0. In the event of a linear temperature dependence, the former equation can be simplified: dI/dT = 100deltaDeltaCp/2TDeltaS(CH2). The deviation from linearity (higher d2I/dT2) increases with increasing deltaDeltaCp values. The model equations were tested from the dataset published by the Kováts group on C78 (19,24-dioctadecyldotetracontane), POH (18,23-dioctadecyl-1-untetracontenol), PCN (1-cyano-18,23-dioctadecyluntetracontane) and TMO (1,38-dimethoxy-17,22-bis-(16-methoxyhexadecyl)-octatriacontane) and by present measurements on the Innowax phase.

Retention indices in the analysis of food aroma volatile compounds in temperature-programmed gas chromatography: Database creation and evaluation of precision and robustness

A retention index (RI) database containing 250 volatile compounds was created on a polar stationary phase column and validated for food aroma characterisation. Precision of the retention indices (RIs) was assessed by performing replicated injections of a representative number of volatiles under the same experimental conditions: differences lower than 1 U were observed for all the compounds. Robustness was evaluated by carrying out injections of the same set of volatile compounds under different experimental conditions, i.e. program temperature, column batches and instrumentation. Excellent results were obtained with a maximum difference in the RI values of 10 U. The capabilities of the created database for food aroma characterisation were finally evaluated by analysing the volatile fractions of different food matrices such as dry sausages, cheese and bread. A great number of volatile compounds were identified in the analysed samples on the basis of their RI, thus proving the usefulness of the RI collections in the field of food analysis.

Temperature-programmed retention indices for gas chromatography–mass spectroscopy analysis of plant essential oils

A total of 95 volatile compounds from the essential oil in buds of Syringa oblata Lindl (lilac) were identified by gas chromatography-mass spectrometry (GC-MS) combined with heuristic evolving latent projections (HELP) and moving subwindow searching (MSS). The identified compounds are mainly aliphatic, terpenes and aromatic compounds. Their temperature-programmed retention indices (PTRIs) on HP-5MS and DB-35MS at three heating rates of 2, 4 and 6 degrees C/min from 80 to 290 degrees C were obtained, which showed that aliphatic compounds give nearly constant PTRIs and PTRIs of terpenoids do not vary much at different heating rates. But PTRIs of aromatic compounds exhibit relatively large temperature dependence. PTRIs vary much more on DB-35MS than those on HP-5MS according to the compound types. In general, differences of PTRIs between the two columns increase from aliphatic compounds to terpenoids to polycyclic aromatic compounds. The PTRIs in different heating rates were used as cross-references in the identification of components in the essential oil. When they were used in analysis of essential oil from flowers of lilac, good results were obtained. These PTRIs would be a part of our PTRI database being constructed on components from plant essential oils. The results also showed that efficiency and reliability were improved greatly when chemometric method and PTRIs were used as assistants of GC-MS in identification of chemical components in plant essential oils.

Determining the vapour pressures of plant volatiles from gas chromatographic retention data

The frequently used vapour pressure versus Kováts retention index relationship has been evaluated in terms of its universal applicability, highlighting the problems associated with predicting the vapour pressures of structurally divergent organic compounds from experimentally measured isothermal Kováts retention indices. Two models differing in approximations adopted to express the activity coefficient ratio have been evaluated using 32 plant volatiles of different structural types as a test set. The validity of these models was established by checking their ability to reproduce 22 vapour pressures known from independent measurements. Results of the comparison demonstrated that (i) the original model, based on the assumption of equal activity coefficients for the test and reference substances, led, as expected, to a poor correlation (r2 = 89.1% only), with significantly deviating polar compounds and (ii) the model showed significant improvement after incorporating a new empirical term related to vaporization entropy and boiling point. The addition of this term allowed more than 99% of the vapour pressure variance to be accounted for. The proposed model compares favourably with existing correlations, while having an added advantage of providing a convenient tool for vapour pressure determination of chemically divergent chemicals.