Frédéric Mercier

Effect of nitrite on the odourant volatile fraction of cooked ham

The aim of this work was to reliably identify the key odour compounds in cooked ham and acquire new knowledge on the role of sodium nitrite on the formation of its aroma. Gas chromatography coupled with mass spectrometry and (or) olfactometry was used. In all, 24 odourants were identified in the volatile fraction of cooked ham. Their main origins are discussed. Orthonasal sniffing of the hams was used to study how these substances contributed to the overall aroma of the product. The aroma of cooked ham is a balance between that of certain sulfur compounds produced during cooking and that of oxidation compounds commonly found in cooked meats. In the absence of nitrite, this balance is disturbed by extensive formation of oxidation compounds that mask the meaty notes induced by the sulfur compounds.

Assessment of comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry based methods for investigating 206 dioxin-like micropollutants in animal-derived food matrices.

This paper evaluates different multiresidue methods based on comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF/MS) to analyze dioxin-related micropollutants in complex food matrices. In a first step, the column sets Rtx-PCB/BPX-50 and Rtx-Dioxin2/BPX-50 were compared in terms of peak shape (width and symmetry) and resolution for the separation of polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) in solvent. A satisfactory separation of 206 dioxin-related micropollutants including the 17 toxic PCDD/Fs was achieved in 75 min with the column set Rtx-Dioxin2/BPX-50. In a second time, the GC×GC-TOF/MS method was spread to the analysis of dioxin-related micropollutants in complex food matrices. An extraction procedure including accelerated solvent extraction (ASE), centrifugal evaporation and gel permeation chromatography (GPC) was optimized. Starting with meat as a model matrix, a micropollutant spiking method was then set up by comparing seven methods in terms of recoveries and reproducibility. The method combining immersion of the meat in a large volume of solvent containing micropollutants followed by homogenization by blender induced recoveries in the acceptable range of 70-130% and satisfactory standard deviations (≤10%) for most of the compounds studied. Limits of detection of the GC×GC-TOF/MS method ranged between 50 and 100 pg/g of spiked fresh meat for PCBs and between 65 and 227 pg/g for PCDD/Fs. Potential applications of this method are discussed.

Relevance of two-dimensional gas chromatography and high resolution olfactometry for the parallel determination of heat-induced toxicants and odorants in cooked food.

The assessment of the dual impact of heating treatments on food safety and aroma is a major issue for the food sector. The aim of the present study was to demonstrate the relevance of multidimensional GC techniques, olfactometry and mass spectrometry for the parallel determination of process-induced toxicants and odorants in food starting with cooked meat as a food model. PAHs were analyzed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry after extraction by accelerated solvent extraction (ASE-GC × GC-TOF/MS). Odour-active compounds were determined by dynamic headspace-GC hyphenated with eight booth olfactometry and mass spectrometry (DH-GC-MS/8O) and DH-heart-cutting multidimensional GC hyphenated with olfactometry and mass spectrometry (DH-GC-GC-MS/O). For PAH determination, the GC × GC conditions consisted of a combination of a primary non-polar BPX-5 column and a secondary polar BPX-50 column, and a modulation period of 5s. In terms of linearity (R(2) ranging from 0.985 to 0.997), recovery rate (84-111%) and limit of detection (5-65 ng/kg of cooked meat), the ASE-GC × GC-TOF/MS method was found consistent with the multiresidue determination of 16 PAHs including benzo[a]pyrene in cooked meat. For aroma compounds, DH-GC-MS/8O and DH-GC-MS/O revealed 53 major meat odour-active compounds. A customized heart-cutting GC-GC-MS/O enabled the coeluting odour zones with high odour-activity to be resolved and revealed 15 additional odour-active compounds. Finally, these developments of multidimensional approaches were used to investigate the balance between 16 PAHs and 68 odour-active compounds generated with different cooking techniques.

Effect of added thiamine on the key odorant compounds and aroma of cooked ham

This study shows that thiamine plays a major role in the formation of three key odorants of cooked ham: 2-methyl-3-furanthiol, 2-methyl-3-methyldithiofuran, and bis(2-methyl-3-furyl)disulphide. Analyses revealed that under identical cooking conditions, the productions of these three aroma compounds increase in a closely intercorrelated way when the dose of thiamine increases. Using a specific 2-methyl-3-furanthiol extraction-quantification method, it was possible to relate the amounts of thiamine added in model cooked hams to the amounts of 2-methyl-3-furanthiol produced in the cooking process. Sensory analyses highlighted the role of thiamine as a precursor of cooked ham aroma.

Effects of pan cooking on micropollutants in meat.

This work presents the effects of pan cooking on PCBs, PCDD/Fs, pesticides and trace elements in meat from a risk assessment perspective. Three different realistic cooking intensities were studied. A GC×GC-TOF/MS method was set up for the multiresidue analysis of 189 PCBs, 17 PCDD/Fs and 16 pesticides whereas Cd, As, Pb and Hg were assayed by ICP-MS. In terms of quantity, average PCB losses after cooking were 18±5% for rare, 30±3% for medium, and 48±2% for well-done meat. In contrast, average PCDD/F losses were not significant. For pesticides, no loss occurred for aldrin, lindane, DDE or DDD, whereas losses exceeding 80% were found for dieldrin, sulfotep or phorate. Losses close to the margin of error were observed for trace elements. These results are discussed in light of the physicochemical properties of the micropollutants as well as of water and fat losses into cooking juice.