GC-O of Static Headspace Samples

The highly volatile odorants are not detected or are underestimated when the screening method is applied to an aroma extract. These compounds are lost when the extract is concentrated or they are masked in the gas chromatogram by the solvent peak. To overcome this limitation, the screening has to be completed by GC-O of static headspace samples (GCOH Fig. 16.3) [59-61]. 

In the sample of parsley (Table 16.5), the analysis was started with a head-space volume of 5 mb, in which GCOH revealed 15 odorants. Then, the head-space drawn from the sample was reduced in a series of steps to find the most potent odorants. GCOH of volumes of 2.5 and 1.25 mb indicated only seven and five odorants, respectively (Table 16.5) after reduction to 0.6 mb, only methane-thiol, (Z)-3-hexenol and an unknown compound were the most potent, highly volatile odorants of parsley [31]. 

In most cases the concentrations of the compounds detected by GCOH are too small for the identification experiments however, this disadvantage can be overcome when the odorants present in food are first detected in the extract by GC-O and then identified. Some of these odorants are also found by GCOH. As their odour quality, GC properties and chemical structures are known, they are easily identified in the headspace sample. In the case of parsley, a comparison of Fig. 16.2 with Table 16.5 indicates that odorant nos. 4, 6, 9, 11, 12 and 15 (Table 16.5) were known from AEDA. Further applications of GCOH are reviewed in [1]. 

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