No abstract

No abstract

This recommended practice enables the quantification of volatile compounds in flavourings to be made by gas chromatography with flame-ionization detection, without having authentic compounds available, and also in many cases it can avoid time-consuming calibration procedures. The relative-response factors (RRF) can be predicted from the molecular formula of the compound, and this approach can be applied to compounds containing the atoms C, H, O, N, S, F, Cl, Br, I, and Si, providing that the molecular formula and number of benzene rings in the analytes are known. The purity of chemicallydefined flavouring substances or chromatographic standards can also be estimated using these predicted RRF, and this procedure can also be used to quantify (poly)hydroxylated compounds, after their derivatization into trimethylsilyl ethers or esters.

Thermal degradation of several possible precursors of the intense flavor compound trans-4,5-epoxy-(E)-2-decenal in model experiments revealed that the odorant is formed in significant yields from 13-hydroperoxy-9,11~ctadecadienoic acid (13-HPOD) and 9-hydroperoxy-10,12-octadecadienoic acid (9-HPODt. Of these hydroperoxides, arising in equal amounts during autoxidation of linoleic acid, the 9~HPOD was established as the more effective precursor. The key intermediates in the generation of the epoxyaldehyde were found to be 2,4-decadienal, arising from 9-HPOD, and 12,13~epoxy-9-hydroperoxy-10~ctadecenoic acid, a degradation product of 13-HPOD. Isolation and characterization of the precursors from a baking margarine confirmed glycerine-bound 9-and 13-HPOD as the intermediates in the formation of the epoxyaldehyde during heating of fats that contain linoleic acid. KEY WORDS: Autoxidation, baking margarine, 4,5-epoxy-(EF2decenal, flavor formation, flavor precursors.The flavor compound trans-4,5-epoxy-(E)-2-decenal (ED) has been reported among the volatiles of thermally degraded trilinolein (1). This odorant, exhibiting the extremely low odor threshold of 0.5 pg/L air (2), was shown to contribute to the green, hay-like off-odor in soybean oil stored in the dark (3) and to the warmed-over flavor of stored beef (4). Furthermor~ ED has been detected among the odorants of wheat bread crumb (2), popcorn (5) and roasted sesame seeds (6). Model studies have revealed that the epoxyaldehyde is formed among other volatiles during thermal degradation of methyl 12,13-epoxy-9~hydroperoxy-10-octade ~ cenoate (7). Because this hydroperoxide has been characterized as a degradation product of methyl 13-hydroperoxy-9,11-octadecadienoate (13-HPOD)(8,9) a reaction scheme leading from linoleic acid to the epoxyaldehyde has been suggested (3).Based on the results of an aroma extract dilution analysis and the calculation of odor activity values, we have recently (10) identified ED as one of the main contributors to the green, lard-like fatty odor of puff-pastries prepared with a baking margarine (shortening). Previously, a homologue of ED, 4,5-epoxy-(E)-2-heptenal, had been reported to cause a fishy-tainted off-flavor in butterfat (11). The odor threshold of the epoxyheptenal is, however, a factor of 106 higher than the odor threshold of ED (2).Because no exact quantitative data on the generation of ED from the postulated precursor compounds are available in the literature the aim of this investigation was to measure the liberation of ED from different precursors in model experiments and to isolate and characterize its precursors from a commercial baking margarine by means of a stable~isotope dilution assay.

No abstract