Juan M. Sánchez

For many reasons (history, myth, oil quality, etc.) olive is unique among the commercially important oil crops. The biochemistry of the olive tree is also singular. From the photosynthetic point of view olive is one of the few species capable of synthesising both polyols (mannitol) and oligosaccharides (raffinose and stachyose) as the final products of the photosynthetic CO2 fixation in the leaf cell. These carbohydrates, together with sucrose, can be exported from the leaves to the fruits to fulfil the metabolic requirements for oil synthesis. On the other hand, contrary to oilseeds, which are absolutely dependent on the leaves to supply photoassimilates for the synthesis of storage oil, developing olives contain active chloroplasts capable of fixing CO2. Thus, the olive contributes to its own carbon economy. In fact, detached olives have been demonstrated to be capable of fixing radiolabelled CO2 in the light and using the reduced photosynthetic products to form storage oil. Soluble fractions from olive pulp have been demonstrated to catalyse the synthesis of fatty acids from malonyl-CoA. The properties of this subcellular fraction indicate that fatty acids are formed by the same type of fatty acid synthase complex established for other plant systems. By the same token, glycerolipids, including storage triacylglycerols, are formed from glycerophosphate and acyl-CoAs according to the Kennedy pathway, as it has been demonstrated in particulate fractions from olive pulp and tissue culture. Also unique to virgin olive oil is its characteristic aroma. The most abundant volatile compounds in the aroma of olive oil are aldehydes and alcohols of six carbon atoms. Such compounds are formed from linoleic and α-linolenic acids through a sequence of enzymatic reactions known as the lipoxygenase pathway, which is stimulated when olives are crushed during the process of oil extraction. The properties of the different reactions involved in the metabolic pathway leading to the formation of such volatile compounds are described in this paper.

The combination of a tandem column ensemble and an on-line microsorption trap is used for the analysis of organic compounds in human breath samples. The four-bed sorption trap uses a series of discreet sorption beds containing three grades of graphitized carbon and a carbon molecular sieve to quantitatively remove most organic compounds from 0.8-L breath samples. The trap is then heated to 300 degrees C in approximately 1.5 s and maintained at this temperature for 10 s. The resulting vapor plug width is in the range 0.7-1.3 s for the compounds found in the breath samples. The separation is performed with a 15-m-long, 0.25-mm-i.d. capillary using a 0.5-microm-thick film of nonpolar dimethyl polysiloxane coupled in series to a polar column, either trifluoropropylmethyl polysiloxane or poly(ethylene glycol). Both column combinations are successful in separating the early-eluting compounds acetone, isoprene, pentane, methyl alcohol, and ethyl alcohol, which are all common in breath samples. The poly(ethylene glycol) combination gave better separation but showed relatively fast deterioration for repeated analysis of wet samples. Breath samples were obtained under different conditions (smoker, nonsmoker, gum chewer), and 25 compounds were identified in the various samples. Many additional peaks are observed but not identified. Analytical curves (log-log) of peak area versus sample volume for test compounds are linear in the range 80-800 cm3. Detection limits (3sigma) for several volatile compounds in 800-cm3 samples are in the 1-5 ppb range.

A method for the determination of volatile organic compounds (VOCs) at sub-trace levels in breath samples based on a multibed sorption trap for the collection and concentration of VOCs, a comprehensive multidimensional gas chromatograph (GCxGC) for the separation of complex mixtures, and a time-of-flight mass spectrometer detector is designed and developed. The good performance of the trap tube device developed for the concentration together with the high sensitivity and separation power of the GCxGC results in a powerful system. In the analysis of samples, more than 100 different compounds are detected of which between 65 and 85 are clearly identified. A total of approximately 250 different compounds are observed in all the samples evaluated of which 142 are identified. A preliminary study to evaluate breath biomarkers for active smoking is performed. The levels of previously described biomarkers are found to be strongly time-dependent with amounts found approximately 1 h after smoking returning to the levels found in nonsmoking volunteers. However, 2,5-dimethylfuran, 2-methylfuran, and furan are found to be effective biomarkers given that they were only found in samples taken from smokers and could still be detected more than 2 h after smoking.