Headspace sampling cheese samples

Femandez-Garcia, E. (1996). Use of headspace sampling in the quantitative analysis of artisanal Spanish cheese aroma. J. Agric. Food chem. 44,1833-1939. 

Concentrations of methanethiol measured in headspace samples of the experimental cheeses are summarized in Table II for the analysis times of 1 day, 21 days and 4 months for each of the two ripening conditions employed. Notably, the cheese made with only encapsulated buffer did not contain methanethiol after 1 day at either temperature. However, the encapsulated methioninase system yielded significant amounts of methanethiol at 1 day, and continued to increase through 4 months. Generally, the final concentration of methanethiol in the encapsulated-buffer control... 

The sample chamber is set to a temperature of 40 C for pre-heating and extraction. This temperature was chosen for a good representation of the released VOCs of the cheeses as a mock-up of the typical mouth feeling. In this dynamic headspace sampling step the volatile headspace is flushed from the cheese samples by using the inert gas nitrogen for collection onto the sorbent packed tubes. After collection the tubes had been transferred to a thermal desorption unit. 

GC combined with mass spectroscopic (MS) detection provides very accurate identification and quantification of FFAs. Pinho et al. (2003) monitored changes in the FFA content during the ripening of ewe cheese. Sampling was done by headspace solid-phase microextraction (SPME). An excellent correlation was observed between the initial concentration of the sample and the amount absorbed on the SPME fiber. SPME sampling was done at 65 °C with a fiber coated with 85-p.m polyacrylate film. After equilibration at 65 °C for 40 min, the fiber was exposed to the sample headspace for 20 min and inserted into the GC port. Despite its accuracy, the GC-MS method is not widely used, presumably because of its cost and complexity. 

Table I, and reflect the Cheddar flavor intensity correlation reported by Manning and coworkers (37). In addition to methanethiol, peaks for dimethyl disulfide were quite large in the aged Cheddar and the Colby cheese headspace profiles, but very little of this compound was found in the mild Cheddar sample.

In the current study, special attention was given to confirming the presence of carbon disulfide in the headspace of Cheddar cheese, and conclusive mass spectral evidence was developed for this compound. The concentration of carbon disulfide varied widely in the samples analyzed for the methanethiol studies, and became quite abundant in the most-aged sample of cheese that contained the encapsulated methioninase system (Figure 6). This sample also contained a lower molecular weight sulfur compound which remains unidentified, but it was observed only in the cheese prepared with encapsulated methioninase. 

A wider range of equipment that has particular features for special applications is described in the hterature. For example, special apparatus has been designed and reported for sampling the headspace of caimed foods and whole cheeses, and from single cigarettes. 

Figure 3.5 Headspace gas chromatography analysis of volatile fatty acids in Dutch cheese after formation of ethyl esters, (a) High-quality cheese. Chromatographic conditions 10 m x 0.53 mm fused silica column coated with HP-1, 60°C (2 min), 10°C min to 140°C. (b) Poor-quality cheese. Sample thermostatted at 80°C. Reproduced from Osl, F., Bestimmung der niederen freien Fettsauren im Hart- und Schnittkase mit der Head-Space Gaschromatographie, Deutsche Molkerei Zeitung, 45, 1516-18, 1988.

The cheese samples were cut and placed in equal amounts into inert-coated heated extraction chambers for release and trapping of the volatile compounds. Nitrogen as an inert gas is passed through the chambers at a constant flow rate while sweeping the headspace vapours onto individual sorbent packed tubes. The used micro-chamber thermal extractor allows up to six samples to be extracted in parallel under identical conditions for comparable results. 

Whey is used in a number of food products, either in production (e.g. ricotta cheese) or as an additive. In comparison to the nose-space investigations mentioned above, work by Gallardo-Escamilla et al. on liquid and fermented wheys dealt only with the headspace volatile composition [61,62]. Using PCA, the VOC data obtained by PTR-MS could be used to differentiate the samples, that is, the mass spectfa of the VOCs emitted resulted in sufficient information to provide a reliable fingerprint of each sample. Furthermore, by applying a simple statistical approach, sensory characteristics such as rancid , caramelized... 

Another investigation of PDO-registered food involved a study of cumin cheese from the Netherlands [94], The headspace VOCs from 30 cumin samples of artisan cheese... 

Figure 8 Comparison of dynamic headspace analyses of 30-mg samples of (top) American cheese and (bottom) Cheddar cheese.

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