Volatile compounds classification

Figure 7.4 Authentication of monovarietal virgin olive oils results of applying stepwise linear discriminant analysis to volatile compounds. Classification was carried out by four volatiles (F)-2-hexenal, butyl acetate, (F)-3-hexenal, 2-methyl-3-buten-2-ol. F-to-Enter was 8.0 tolerance was upper 0.52 for all selected volatiles. Note A, cv. Arbequina C, cv. Coratina K, cv. Koroneiki P, cv. Picual (source SEXIA Group-Instituto de la Grasa, Seville, Spain).

In the last decade much effort has been oriented to the fabrication of artificial olfaction machines able to determine chemical images (also odor images) of complex volatile compounds. Today many different electronic noses and tongues are available for odor detection and classification and for the creation of chemical images of liquids. 

Abstract This chapter reviews chemical structures of biologically active, volatile compounds in beetles. Techniques used for structure elucidation are briefly discussed as well as facts and speculations on the biosynthesis of target compounds. Syntheses of selected substances are cursorily presented. The order of sections follows taxonomic classifications. Depending on the biological significance of relevant compounds in certain taxa, the corresponding sections are again subdivided into attractive compounds (mostly intraspecifically active pheromones) and defensive compounds (mostly interspecifically active allomones). 

The ANN approach has also been applied to compound classification. For example, Drefahl [48] has discussed the ANN approach to discriminate chlorinated organics with respect to their volatility from aqueous solutions. Varmuza [49] has described ANN classification as a standard method in pattern recognition and provides references to its use in spectra interpretation. 

This method has the main aim of detecting attributes and defects, and measuring their intensity, for the classification of the various categories of virgin olive oils (Angerosa, 2001). The sensory attributes perceived by the consumer arise from the stimulation of gustatory and olfactory receptors from a large number of volatile and some non-volatile compounds such as simple and combined phenols. The intensity of each sensation is related to the concentration of chemical compounds identified in the volatile fraction of the oil. 

Volatile A volatile substance is capable of readily changing from a solid or liquid to a vapour or gas. Gives a basis for the concept of classification of aromatic components into top (most volatile), middle (intermediate volatility) and base (least volatile) notes. Used as a noun to denote a volatile compound or substance. 

The structure of the sex pheromone for the Fucus species, fucoserratene (11), was elucidated in 1973.16 The positions and geometries of alkenes were revealed by comparison of the gas chromatographic behavior with those of the isomeric conjugated 1,3,5- and 2,4,6-octatrienes. To date, a series of hydrocarbons and epoxides 1-11 and their stereoisomers have been identified within the pheromone bouquets of more than 100 different species of brown algae.17-23 Identification of these compounds was based on a combination of gas chromatography-mass spectrometry (GC-MS) analysis and by comparison with authentic synthetic compounds. These sex pheromones were all lipophilic, volatile compounds that consisted of C8 or Cn linear or monocyclic hydrocarbons or their epoxides. The monocyclic compounds have a cyclopropane, cyclopentene, or cyclo-heptadiene structure. Interestingly, the relationships between the chemical structures of pheromones and the taxonomical classifications of algae are unclear (Table 1). 

Table 13.18 Results of applying LDA to the data of 10 volatile compounds in order to discriminate the four groups of varietal wines. Classification matrix ...

Marengo, E., Aceto, M., and Maurino, V. (2001). Classification of Nebbiolo-based wines from Piedmont (Italy) by means of solid-phase microextraction-gas chromatography-mass spectrometry of volatile compounds, J. Chromatogr. A, 943,123-137. 

Table 8.1 Discriminant analysis of the volatile compounds of the scents of 4 snapdragon cultivars. The standardized coefficients in bold indicate the volatiles that contributed the most to classification of the snapdragon varieties by each of the functions. The sign and magnitude of the unstandardized coefficients (in bold) indicate which cultivar was best separated from the others by the function. The order of the functions indicates the distance in similarity between the snapdragon cultivars. (From Wright et al., 2005, reproduced with permission of Springer)...

Each sensor element changes its electrical resistance (Rmax) when exposed to volatile compounds. In order to produce consistent data for the classification, the sensor response is presented with a volatile chemical relative to the baseline electrical resistance in fresh air, which is the maximum change in the sensor electrical resistance divided by the initial... 

Homeopathic herbal preparations. Homeopathic products are classified as over-the-counter or prescription drugs and are regulated under the Homeopathic Pharmacopoeia of the United States. Safety concerns that arise for an herb in crude form may not apply to homeopathic preparations of the same herb, and this document does not address herbal products in homeopathic forms. Essential oils. Essential oils are concentrations of specific volatile compounds. While many essential oils have a well-documented history of safe use by appropriately skilled persons, they often present toxicological concerns that are absent or moderate in the crude plant materials from which the oil is derived. Except for a small number of essential oils that have a history of internal use, the classification of essential oils is beyond the scope of this document. 

Figure 5 Classification of 88 white wine samples of three varieties from five producers according to vintage by linear discriminant analysis - plot in the coordinates of two main discriminant functions (DF2 versus DF1) composed of 19 original variables (concentrations of volatile, aroma creating compounds). Explanation of symbols O denote the 1996 samples, x the 1997 samples, -i- the 1998 samples. Probability ellipses express the 95% probability level. (Reproduced with permission from Petka J, Mocak J, Farkas P, Balia B, and Kovac M (2001) Classification of Siovak varietal white wines by volatile compounds. Journal of the Science of Food and Agriculture 81 1533-1539 John Wiley Sons Ltd.)...

Heat treatment of milk ensures the microbial safety of milk and increases its shelf life. Different heat treatments (UHT, pasteurized, sterilized) can be distinguished by analyzing the volatile compounds with an electronic nose. A hybrid system that uses an electronic nose combined with an SVM classification method was tested by Brudzewski, Osowski, and Markiewicz for milk recognition and classification.The electronic nose was composed of seven tin oxide-based gas sensors, and the SVM model was tested with linear and RBF kernels. In the first experiment, four brands (classes) of milk were... 

Carbide decompositions yield no volatile product and, therefore, many of the more convenient experimental techniques based on gas evolution or mass change cannot be applied. This is a probable reason for the relative lack of information about the kinetics of reaction of these and other compounds which are correctly classifed under this heading, such as borides, silicides, etc. 

The grouping of ammonium salts in a separate section serves to emphasize the similarities of behaviour which are apparent in reactions yielding the volatile NH3 molecule, following removal of a proton from the NH4 cation. This property is not unique indeed, many cations are volatile and numerous salts leave no residue on completion of decomposition. Few kinetic investigations have, however, been reported for other compounds, in contrast to the extensive and detailed rate measurements which have been published for solid phase decompositions of many ammonium salts. Comparisons with the metal salts containing the same anion are sometimes productive, so that no single method of classification is altogether satisfactory. 

Organic compounds such as the chlorinated solvents also include a wide range of compounds and do not easily fit into the structural classification as described for petroleum hydrocarbons. Chlorinated hydrocarbons are commonly discussed in terms of their relative density (i.e., LNAPL or DNAPL) or degree of halogenation and degree of volatility (i.e., volatile, semi-volatile). 

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