Chapter 6
Changes in Key Odorants of Sheep Meat Induced by Cooking
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Valerie Rota and Peter Schieberle Deutsche Forschungsanstalt für Lebensmittelchemie, Lichtenbergstrasse 4, D-85748 Garching, Germany Application of the Aroma Extract Dilution Analysis on two extracts prepared from cooked and raw lean sheep meat revealed 4-ethyloctanoic acid (mutton-like), trans 4,5-epoxy -(E)-2-decenal (metallic), (Z)-1,5-octadien-3-one (geranium -like) and (E,E)-2,4-decadienal (deep fried) as important odorants in the cooked as well as in the raw meat, thereby indicating the important role of the raw meat as source of sheep meat odorants. 4-Hydroxy-2,5-dimethyl-3(2H)-furanone and 2-acetyl-1-pyrroline as well as 2-aminoacetophenone were among the few aroma compounds, which were clearly increased in their Flavor Dilution (FD) factors by the cooking procedure. A stable isotope dilution assay showed that 4 -ethyloctanoic acid was by a factor of 4 higher in uncooked intramuscular fat as compared to uncooked adipose tissue, in which 4,5-epoxy-(E)-2-decenal and further lipid degradation were shown to be the most odor-active compounds. The cooking procedure did not much alter the concentration of 4 -ethyloctanoic acid.
As compared to pork or beef meat, the consumption of sheep meat (mutton or Iamb) is on a low level in most of the European countries. For example in Germany, sheep meat accounted for only 1.3 % of the total annual meat used in Germany. The main reason for this is undoubtedly the characteristic sweet-fatty odor developing during cooking of sheep meat, which is regarded as unpleasant and, thus, leads to a negative consumer appraisal. In search of the compounds responsible for this characteristic aroma, Hornstein and Crowe (/) were the first to report on the key role of adipose tissue as source of the species-specific © 2006 American Chemical Society
Shahidi and Weenen; Food Lipids ACS Symposium Series; American Chemical Society: Washington, DC, 2005.
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74 aroma compounds. Because of the intense odor, Wong et al. (2) later suggested branched chain fatty acids, in particular, 4-methyloctanoic and 4-methylnonanoic acid as being responsible for the mutton-like aroma of cooked sheep meat. In a study on the basic volatiles of roasted lamb fat, Buttery et al. (3) identified 2pentylpyridine which, based on its unpleasant odor at a threshold in water of 0.6 pg/L, was suggested as another cause for the consumer rejection of cooked sheep meat. Ha and Lindsay (4) suggested another branched fatty acid, 4-ethyloctanoic acid, as a further odorant contributing to the typical aroma developing in mutton meat during cooking. The same group (J) later proposed several alkylphenols, which were present above their odor thresholds in perinephric mutton fat, as additional odorants possibly responsible for the sheepy-muttony aroma of sheep meat. Guided by the first report of Hornstein and Crowe (/), most of the studies on sheep meat aroma were focused on the formation of such "muttony" smelling odorants generated from adipose tissue. Sutherland and Ames (
