Nathalie Kondjoyan

Fat volatiles tracers of grass feeding in sheep.

Volatile compounds were analysed in subcutaneous fat from lambs raised and finished on grass (GG); raised and finished on concentrates (SS); raised on grass and finished on concentrates for a long (GS1) or a short (GS2) period. Whereas 3-methylindole (skatole), a compound that has been described as a good discriminator of grass feeding, was unaffected by the diet (P>0.05), 2,3-octanedione was lower (P<0.01) in the fat from animals that spent a period in stall with a concentrate diet than in those finished on grass. Among the 20 monoterpenes detected, only p-cymene was affected by the treatment, being higher (P<0.05) in the fat from animals raised and finished on grass (GG) than in the other treatments. Eight among the 13 detected sesquiterpenes were affected by the diet treatment. In particular β-caryophyllene, not detected in the fat from animals raised and finished on concentrates (SS group), was at basal levels in the animals raised on pasture and finished for different durations on concentrates (GS1 and GS2 treatments) and was present at high levels in the animals raised and finished on grass (P<0.0005). From a factorial discriminant analysis, four of the 33 terpenes detected discriminated perfectly those animals raised and finished on pasture (GG) from all the other groups (SS, GS1, GS2).

Traceability of grass feeding in beef: terpenes, 2,3-octanedione and skatole accumulation in adipose tissue of young bulls.

The development of analytical methods to verify the production system of meat products requires the identification of biomarkers that can trace the products origin, and secondly the factors that govern the deposition of these markers in animal tissue need to be defined. In this study, 2,3-octanedione, skatole and terpenes were selected as biomarkers, and their deposition was investigated in bull calves reared under three different strategies. All of the animals were reared indoors until approximately 150 days of age. They were suckled twice a day by their mothers, and both calves and cows had free access to cocksfoot hay. Then the first two groups of animals were kept indoors, suckled by their mothers twice a day and received either cocksfoot hay (HL) or freshly cut-green herbage (GL) and a limited quantity of concentrate. The third group of calves (PH) was kept on pasture with their mothers and offered concentrate ad libitum. The pasture supporting the PH animals was highly diversified, containing several terpene-rich plant species, whereas the herbage for the GL animals contained no species known to be aromatic. Perirenal and subcutaneous adipose tissues were analysed for volatile compounds. The perirenal fat was found to be more responsive to the treatment and a more reliable substrate than the subcutaneous adipose tissue. Higher levels of 2,3-octanedione (P < 0.05) were found in PH and GL than in HL fat (6.56, 6.51 and 5.77 area arbitrary units, respectively, in perirenal fat), confirming the ability of this molecule to trace green herbage feeding. Skatole was detected in the perirenal and subcutaneous fat of all the animals. Animals receiving high concentrate level (PH group) presented lower (P < 0.05) skatole values (5.83 area arbitrary units in perirenal fat) than animals receiving low concentrate level (HL and GL groups, 6.23 and 6.71 area arbitrary units, respectively, in perirenal fat). Terpenoids, and especially sesquiterpenes, were found at higher levels and diversities in the PH than in the GL and HL animals. Two monoterpenoids allowed group discrimination considering perirenal or subcutaneous fat without distinction, whereas 11 and 5 sesquiterpenoids from perirenal and subcutaneous fat, respectively, allowed it.

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.