Flavor Authentication Studies of alpha-Ionone, beta-Ionone, and alpha-Ionol from Various Sources

摘要

In addition to the already available information on the authenticity of alpha- (1) and beta-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 delta13CV-PDB and delta2HV-SMOW values provide for the first time isotope data of such 'natural' 1 and 2 as well as of synthetic and 'ex plant' alpha-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 delta13CV-PDB value of -18.5 per thousand. In addition, the use of synthetic citral resulted in an enriched delta2HV-SMOW value of -43 per thousand, whereas with citral ex Litsea cubeba and ex lemongrass values of -242 and -232 per thousand, respectively, were recorded. IRMS analyses of 'natural' 2 revealed delta13CV-PDB and delta2HV-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 delta13CV-PDB but not the delta2HV-SMOW values. Synthetic 3 showed delta13CV-PDB and delta2HV-SMOW values of -24.5 and -184 per thousand, respectively. These data differed from those found in raspberry fruit under study (n = 8), that is, ranging from -33.6 to -36.6 per thousand for delta13CV-PDB and from -200 to -225 per thousand for delta2HV-SMOW. The values determined additionally for 1 and 2 in raspberry fruit samples ranged from -30.3 to -35.1 per thousand and from -176 to -221 per thousand for delta13CV-PDB and delta2HV-SMOW, respectively, and thus corresponded to the already known literature information. Keywords: Flavor authenticity; alpha-ionone; beta-ionone; alpha-ionol; IRMS; HRGC-C/P-IRMS; 13C/12C ratio; 2H/1H ratio; raspberry (Rubus idaeus).