Flavor Authentication Studies of α-Ionone, β-Ionone, and α-Ionol from Various Sources

In addition to the already available information on the authenticity of α- (1) and -ionone (2) from plant tissues, there is an interest in the stable isotope data of 1 and 2 available by synthesis from citral and acetone, as European Union regulations, in contrast to the United States and other countries, do not allow a product to be declared as 'natural' that has been chemically synthesized (e.g., by using a natural catalyst) from natural educts. Analyses performed by on-line capillary gas chromatography-isotope ratio mass spectrometry in the combustion and pyrolysis modes (HRGC-C/P-IRMS) as well as by elemental analyzers (EA-C/P-IRMS) measuring (delta)13C(V-PDB) and (delta)2H(V-SMOW) values provide for the first time isotope data of such 'natural' 1 and 2 as well as of synthetic and 'ex plant' α-ionol (3). The isotope data recorded for synthesized 1 and 2 reflected the influence of the origin of the used citral, whereas that of acetone was less remarkable. For instance, 'natural' 1 ex citral from lemongrass showed, as expected for a C4 plant, an enriched (delta)13C(V-PDB) value of -18.5”. In addition, the use of synthetic citral resulted in an enriched (delta)2H(V-SMOW) value of -43”, whereas with citral ex Litsea cubeba and ex lemongrass values of -242 and -232”, respectively, were recorded. IRMS analyses of 'natural' 2 revealed (delta)13C(V-PDB) and (delta)2H(V-SMOW) values that were nearly identical to that recorded for 'natural' 1. As to both 1 and 2, variations of synthesis conditions led to distinct changes in the (delta)13C(V-PDB) but not the (delta)2H(V-SMOW) values. Synthetic 3 showed (delta)13C(V-PDB) and (delta)2H(V-SMOW) values of -24.5 and -184”, respectively. These data differed from those found in raspberry fruit under study (n = 8), that is, ranging from -33.6 to -36.6” for (delta)13C(V-PDB) and from -200 to -225” for (delta)2H(V-SMOW). The values determined additionally for 1 and 2 in raspberry fruit samples ranged from -30.3 to -35.1” and from -176 to -221” for (delta)13C(V-PDB) and (delta)2H(V-SMOW), respectively, and thus corresponded to the already known literature information.