Abstract. A dry purge procedure was used to eliminate water during the analysis of the volatile fraction of a water-rich cheese, by dynamic headspace-GC-MS. The impact of the duration of this procedure on chromatographic profile was studied for durations ranging from 0 to 50 minutes. A dry purge duration of 3 minutes sufficed to reduce the water peak area and improve the quality of the chromatographic signal. However, the dry purge procedure induced marked modifications to the chromatographic profile of the cheese throughout the range of component polarities.

Abstract. Artifacts due to water that appear during analysis by purge-and-trap/GC/MS of naturally moist products were reproduced by increasing the relative humidity of the headspace of measuring cell containing dry and low-moisture products (dehydrated beef stock and powdered Parmesan cheese) by means of a piece of moistened glass wool. The changes observed in the chromatographic profiles of the dry products after humidifying the headspace are explained by interactions between volatile compounds, water and the adsorption trap during the purge-and-trap step.

The dynamic headspace technique coupled with gas chromatography and mass spectrometry is frequently used to characterize the volatile fraction of food products [1][2][3][4][5][6][7]. However, water is very often the main volatile component and generates artefacts during the different steps of the analysis [8][9][10]. Several approaches to limit these artefacts have already been tested. They include acting on the sample or the adsorbent [11][12][13][14], inserting a water trap between the sample and the adsorbent [15][16][17][18], modifying injection parameters [19] or selecting a particular type of chromatographic column [20].Water activity in the sample can be lowered simply by mixing in hygroscopic substances such as salts or sugars. To date, many studies have been conducted to evaluate the effect of such substances on the analysis of the volatile fraction of liquids such as apple juice [21], milk [22] or model aqueous solutions [23][24][25][26][27]. These investigations have shown that adding hygroscopic salts increases the vapor pressure and therefore the concentration of the volatile substances in the headspace of samples. However, very little work has been published on the effects of using such salts in solid or semi-solid media [28].The objective of this work was therefore to determine whether or not the incorporation of various hygroscopic salts into cheese, which modifies both the structure and the physical and chemical properties of the product, could facilitate the analysis of its volatile fraction, and if so to what extent. Materials and methods SamplesCommercial wax-coated pre-portioned hard processed cheeses were selected (mini-Babybel ® ). Such samples are biochemically stable, homogeneous, and have a relatively simple volatile fraction. Their water content was 48 % and the relative humidity of their headspace was 72 %. Storage of samplesThe cheese samples in their original wax packaging were wrapped in aluminium foil, vacuum-sealed in polyethylene bags and stored at -25°C. Before each analysis the sample was left overnight at room temperature. Choice of saltsFive salts were chosen for their hygroscopic properties and their low reactivity toward the matrix of the products stud- n°28 114.365). The salts were dehydrated in an oven at 105°C before use. To determine the least quantity of salts necessary to obtain a dense homogeneous mixture with medium particle size, preliminary tests were conducted on the texture of the cheese-salt mixtures. For 4 g of cheese the quantities of salt to be added were: 4 g of calcium chloride, 2 g of magnesium sulfate, 6 g of potassium carbonate, 10 g Abstract. We investigated the effect of adding hygroscopic salts on the analysis by dynamic headspace -gas chromatographymass spectrometry of the volatile fraction of cheese. We tested five salts: calcium chloride, magnesium sulfate, potassium carbonate, sodium chloride and sodium sulfate. Relative humidity of the headspace, pH value of the matrix, desorption of volatile components and their odor were modified differentl...

Abstract. The insertion of a condenser in the dynamic headspace -GC-MS analysis circuit allows part of the water contained in a water-rich sample to be condensed. The impact of such a condenser on the chromatographic profiles of a cheese was studied for temperatures ranging from -12 to 0°C. The condenser collected the water, but also some of the volatile components of the cheese, irrespective of its operating temperature. Insertion of a condenser improved the overall quality of the chromatographic signal, but caused major changes in the chromatographic profile of the cheese.