Hazelnut roasting, filbertone

Methyl-(E)-2-hepten-3-one (filbertone) has been identified as character impact odorant of roasted hazelnuts [90-92]. Its odour threshold is extremely low 5 ng/kg (water as solvent). 

Of special iirportance for the aroma of nougat is FUbertone, 5-methyl-(E)-2-hepten-3-one (odor threshold 5 ng/kg oil), which is produced during the roasting of hazelnuts. In a model experiment, the concentration of this compound increased at 180 °C from 1.4 to 660 pg/kg in 9 min and to 1150 pg/kg in 15min. In fact, 315pg/kg were found in a commercially produced oil from roasted nuts. Oil from unroasted nuts contains less than 10 pg/kg Filbertone. 

The presence of methylketones is undesirable in some fats, such as butter, coconut and pahn oil. Also undesirable are unsaturated ketones produced by oxidation of fatty acids, which are called alkyl vinyl ketones. For example, pent-l-en-3-one (8-47) smells of fish oil, oct-l-en-3-one (8-47) has a metallic taste, and (Z)-octa-l,5-dien-3-one (8-47) has an oily, greasy and metallic taste. A related ketone similarly formed by oxidation of fatty acids is (E)-5-methylhept-2-en-4-one (8-47), known as filbertone (Table 8.1), a key component of the odour of hazelnut and some chocolate products, such as nougat. Its content in raw nuts is low (about 1.4p,g/kg), but increases to 660p,g/kg in nuts roasted at 180 °C for 9 minutes, and to 1150p,g/kg in nuts roasted for 15 minutes. Hazelnuts contain a mixture of (-F)-(2E,5S)- and (-)-(2E,5R)-isomers (8-47). The enantiomeric composition of raw hazelnuts... 

The character impact compound of hazelnuts, ( )-5-methyl-2-hepten-4-one (filbertone), undergoes isomerization during the roasting process (62). Of the four possible geometric and enantiomeric isomers formed, all exhibit the typical... 

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