Flavor Profiling of Milk and Premium Teas by HiSorb Sorptive Extraction with Thermal DesorptionGCMS Analysis

This study shows that the organic compounds giving rise to the flavor of beverages can be identified by high-capacity sorptive extraction using PDMS probes, with analysis by thermal desorption–GC–MS.

Analysis of volatile and semi-volatile organic compounds (VOCs and SVOCs) in foods and beverages is important for quality control and product development/characterisation, and widely studied using GC–MS, but hindered by the limitations of existing sample preparation techniques.

Markes International's PDMS HiSorb^(tm) probes allow immersive sorptive extraction from liquids (or headspace sorptive extraction from solids or liquids), without the expense of time associated with solvent-extraction methods, and with lower detection limits than SPME.

In this pair of studies, a HiSorb probe (Figure 1) was immersed into a 20 mL headspace vial, containing either (a) a mixture of semi-skimmed milk and analytical-grade water (1:1) or (b) freshly-brewed tea. The vial and probe were agitated on a HiSorb Agitator at 40 °C for 1 h, and the probe was then washed, dried, and inserted into an industry-standard 3.5-inch TD tube for desorption. Analysis used a TD100-xr^(tm) thermal desorber (Markes International), a DB-5 column (for milk) or DB-624 column (for tea), and a quadrupole mass spectrometer used in scan mode.

Analysis of Milk

Figure 2 shows the complex profile obtained and the analyte range achievable with this analytical system-compounds ranged in volatility from C₃ to C₁₉ and included alkanes, aldehydes, alcohols, acids, esters, ketones, and lactones. The latter are particularly important flavor compounds, and in this example four ?-lactones were identified. To assess their relative concentrations, Figure 3 shows an extracted-ion chromatogram (EIC) at m/z 99, which is a principal fragment ion for these compounds. ?-Dodecalactone (#25) predominates within this group, and therefore could be judged to be a contributor to the flavor of this milk.

Analysis of Earl Grey, Vanilla Chai, and Ceylon Teas

All three teas show complex profiles with a large number of components at high and low levels (Figure 4). Characteristic components of the citrus fruit bergamot in the Earl Grey tea are limonene (#9), linalool (#14), and linalyl acetate (#23), while the vanilla-derived compounds eucalyptol (#11), anethole (#26), and coumarin (#35) are recovered from Vanilla Chai. The Ceylon tea shows some similar compounds to the other samples, such as linalool (#14) and eugenol (#33), but also some unique compounds, including 2-propylfuran (#10), phenylethyl alcohol (#17), and trans-cinnamaldehyde (#29).

Conclusions

HiSorb probes are an easy-to-use, highly sensitive approach to the sorptive extraction of VOCs and SVOCs from a range of sample types, including water-based solutions, emulsions, and suspensions, as well as solids. Unattended sample preparation, with automated analysis by thermal desorption (TD), ensures maximum sensitivity and productivity, while re-usable probes and tubes minimize the cost per sample.

Markes International

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