Characterization of the key odorants in raw Italian hazelnuts ( Corylus avellana L. var. Tonda Romana) and roasted hazelnut paste by means of molecular sensory science.

The concentrations of 19 odorants, recently characterized by GC-olfactometry and aroma extract dilution analysis as the most odor-active compounds in raw hazelnuts, were quantitated by stable isotope dilution assays (SIDA). Calculation of odor activity values (OAV) on the basis of odor thresholds in oil revealed high OAVs, in particular for linalool, 5-methyl-4-heptanone, 2-methoxy-3,5-dimethylpyrazine, and 4-methylphenol. A model mixture in sunflower oil containing the 13 odorants showing OAVs above 1 in their natural concentrations resulted in a good similarity compared to the overall nut-like, fruity aroma of the raw hazelnuts. Quantitation of the 25 most odor-active compounds in roasted hazelnut paste by SIDA showed clear changes in the concentrations of most odorants, and formation of new odor-active compounds induced by the roasting process was observed. The highest OAVs were calculated for 3-methylbutanal (malty), 2,3-pentanedione (buttery), 2-acetyl-1-pyrroline (popcorn), and (Z)-2-nonenal (fatty), followed by dimethyl trisulfide, 2-furfurylthiol, 2,3-butanedione, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone. The aroma of a model mixture containing the 19 odorants with OAVs above 1 in their actual concentrations in the roasted nut material was judged to elicit a very good similarity to the popcorn-like, coffee-like, and sweet-smoky aroma of the roasted hazelnut paste. New SIDAs were developed for the quantitation of 5-methyl-4-heptanone, 5-methyl-(E)-2-hepten-4-one, 2-thenylthiol, and 3,5,5-trimethyl-2(5H)-furanone.

Changes in the key odorants of Italian Hazelnuts ( Coryllus avellana L. Var. Tonda Romana) induced by roasting.

Application of a comparative aroma extract dilution analysis on aroma distillates isolated from either raw Italian hazelnuts or a roasted hazelnut material produced thereof revealed 37 odor-active compounds in the raw nuts, whereas 46 aroma compounds were detected in the roasted nut material. 2-Methoxy-3-isopropylpyrazine and 2-methoxy-3,5-dimethylpyrazine as well as 5-methyl-4-heptanone predominated with the highest flavor dilution factors in the raw nuts, whereas 2-acetyl-1-pyrroline, 2-propionyl-1-pyrroline, 2-furfurylthiol, and 2-thenylthiol as well as (Z)-2-octenal, (Z)-2-nonenal, and (Z)-2-decenal showed the highest odor activities in the roasted nuts. These odorants, as well as several others, were previously unknown in hazelnuts. In addition, the intensely seasoning-like smelling 3,5,5'-trimethyl-2(5H)-furanone was identified for the first time as a food aroma compound on the basis of a newly developed synthetic route and NMR measurements.