Odorants enrichment

Diet may counteract or substitute for chemical cues that influence sexual maturation. Male California voles, Microtus californicus, for instance, are inhibited in their sexual development by odors from their mothers or unrelated females. This effect is eliminated if the regular diet is enriched with fresh lettuce. In young females, uterus growth is stimulated by the odor of males but, in the absence of males, fresh lettuce added to the diet can accomplish the same effect (Rissman and Johnston, 1986). This can be seen as another case of adaptive redundancy of cues for an important function. 

Apart from petrochemical and environmental applications [12], classical MDGC was/is used in the flavour field mainly for enrichment and identification of odorous trace compounds in complex mixtures, or for authenticity evaluation by chiral separation or isotopic ratio determination. In Table 15.1 some typical applications are given. 

In most cases only a few odorants selected for identification appear as clear peaks in the gas chromatogram. The majority of the odorants are concealed by peaks of the volatiles predominating in the extract. To enrich the odorants the extract is separated into the acid and the neutral/basic fractions and the latter is separated by chromatography on silica gel [21, 27]. If necessary, the fractions... 

Once an internal standard is available, the analysis can be easily performed the food sample is spiked with an appropriate amount of the labelled standard and then the volatile fraction is isolated by solvent extraction and sublimation under a high vacuum (cf. Figure 1). If required, the odorants and the internal standards are enriched by liquid chromatography... 

Some reference odorants are commercially available some have to be synthesized in the laboratory. Sometimes or often, the concentration of an important odorant in a sample might be so low, that even after enrichment and purification,... 

Crust volatiles were isolated immediately after baking by extraction with dichloromethane and sublimation in vacuo ( ). Application of aroma extract dilution analysis 6) to the acid-free crust extract led to the detection of 31 odorants. After separation and enrichment, these compounds were identified by comparison of the MS/EI, MS/Cl and retention data on two columns of different polarity to reference compounds. Aroma quality was also assessed. The results of the identification experiments (Table I) revealed that 2(E)-none-nal (No. 1), followed by 2(E),4(E)-decadienal (No. 2) and 3-methyl-butanal (No. 3) showed the highest FD-factors in the crust of the chemically leavened bread. Additionally l-octen-3-one, 2(Z)-nonenal, 2(E),4(E)-nonadienal and an unknown compound with a metallic odor contributed high FD-factors to the overall flavor (For a discussion of FD-factors, see Chapter by Schieberle and Grosch, this book). 

A knowledge of botany enriches the understanding of natural perfume materials and their production but is not essential to the perfumer s job. An interest in the physiology of olfaction and the mechanisms of odor detection is intellectually enriching, but at the current state of knowledge this discipline contributes little to the practice of perfumery. 

Of the two interesting cases 2 and 3, the third case requires further concentration and enrichment of the sample until a physically measurable signal is obtained. In case 2 it is possible to deduce the structure of the substance with the combination of the mass spectrum with the retention time. It must be mentioned that often false interpretations are made using this method when the physically measured peak from a sufficiently concentrated sample contains overlapping peaks of an odorless substance and an odor active substance. 

Gas chromatography-olfactometery (GC-O) provides a sensory profile of odor active compounds present in an aroma extract by sniffing the GC effluent. Several techniques have been developed to collect and process GC-O data and to estimate the sensory contribution of individual odor active compounds, including dilution analysis (29, 30), time intensity (31), and detection frequency (32) methods. GC-O has successfully been used to evaluate the odor active compounds of olive oil (33), soybean oil (34), and fish oil enriched mayonnaise (35). 

Rochefort C, Gheusi G, Vincent J-D, Lledo P-M. 2002. Enriched odor exposure increases the number of newborn neurons in the adult olfactory bulb and improves odor memory. J Neurosci 22 2679-2689. 

---