Development of a stable isotope dilution assay for the quantification of 5-methyl-(E)-2-hepten-4-one: Application to hazelnut oils and hazelnuts

A stable isotope dilution assay was developed for the quantitation of the h azelnut odorant 5-methyl-(E)-2-hepten-4-one by mass chromatography using sy nthesized [H-2](2)-5-methyl-(E)-2-hepten-4-one as the internal standard. Ap plication of the method on two hatches of commercial hazelnut oils, process ed from either roasted or unroasted nuts, revealed 6.4 mu g 5-methyl-(E)-2- hepten-4-one per kg of unroasted oil whereas 315.8 mu g per kg was determin ed in the roasted nut oil. The about 50-fold higher amount of 5-methyl-(E)- 2-hepten-4-one in roasted hazelnut oil suggested the necessity of a thermal treatment to generate the flavor compound. Pan frying of raw hazelnuts (9 to 15 min) or belling of the crushed nut material for 1 h in water led to a n increase of 5-methyl-(E)-2-hepten-4-one by factors of 600 and 800, respec tively, thereby corroborating that the major part of the nut flavorant is f ormed during heat treatment from a yet unknown precursor in hazelnuts.