Multidimensional Gas Chromatography of Organosulfur Compounds in Coffee and Structure-Odor Analysis of 2-Methyltetrahydrothiophen-3-one.

Organosulfur compounds (OSCs) in coffee remain challenging to analyze by conventional gas chromatography (GC) due to their low concentrations amid coffee's complex matrix and susceptibility to chiral-odor influences. In this study, multidimensional GC (MDGC) methods were developed to profile OSCs in coffee. Conventional GC was compared to comprehensive GC (GC×GC) for untargeted OSC analysis in eight specialty coffees, and GC×GC was found to improve the fingerprinting of OSCs in coffee (50 vs 16 OSCs identified). Of the 50 OSCs, 2-methyltetrahydrothiophen-3-one (2-MTHT) was of high interest due to its chirality and known aroma contribution. Following that, a heart-cutting method for chiral GC (GC-GC) was developed, validated, and applied to the coffees. The mean enantiomer ratio of 2-MTHT was observed to be 1.56 (R/S) in brewed coffees. Overall, MDGC techniques allowed for more comprehensive analyses of coffee OSCs, from which (R)-2-MTHT was found to be the predominant enantiomer with the lower odor threshold.

A high-throughput analysis of volatile compounds with various polarities using headspace stir bar sorptive extraction.

Long sample extraction time is usually necessary in the analysis of volatile flavour compounds to achieve high extraction efficiency. However, the long extraction time reduces sample throughput, which results in waste of labour and energy. Therefore, in this study, an improved headspace-stir bar sorptive extraction was developed to extract volatile compounds with varying polarities in a short time. With the aim of achieving high throughput, extraction conditions were selected and optimised based on the combinations of different extraction temperatures (80-160 °C), extraction times (1-61 min), and sample volumes (50-850 µL) through the response surface methodology with Box-Behnken design. After obtaining the preliminary optimal conditions (160 °C, 25 min, and 850 µL), the effect of cold stir bars with shorter extraction time on the extraction efficiency was evaluated. The cold stir bar improved the overall extraction efficiency with better repeatability, and the extraction time was further shortened to 1 min. Then, the effects of different ethanol concentrations and salt additions (sodium chloride or sodium sulfate) were studied, and 10% ethanol concentration with no salt addition provided the highest extraction efficiency for most compounds. Finally, it was verified that the high-throughput extraction condition was feasible for the volatile compounds spiked in a honeybush infusion.

Direct coupling of supercritical fluid extraction to a gas phase atmospheric pressure chemical ionisation source ion trap mass spectrometer for fast extraction and analysis of food components.

Supercritical fluid extraction (SFE) was coupled to a custom-built atmospheric pressure chemical ionization (APCI) source of an ion trap mass spectrometer (ITMS). This method was developed for the monitoring of static or dynamic carbon dioxide extraction of volatile aroma compounds in real time. The gas phase APCI source resulted in simple spectra where the extraction of individual compounds could be monitored. A classical mint extraction was used to demonstrate the possibilities of the method. Influence of cell loading and standard injection possibilities are described. Limit of detection of the system was 0.5 nl or lower for a series of test compounds. Prospect for a fast method for extraction and quantification was raised and discussed.