Volatile fractions, analysis

MacKinnon MD (1977) The analysis of the total organic carbon in seawater a. Development of methods for the quantification of TOC b. Measurement and examination of the volatile fraction of the TOC. PhD Dissertation. Dalhousie University... 

As reported in the previous section, AEDA is performed with a concentrated aroma extract. However, concentration of the volatile fraction might lead to losses of odorants, e.g. by evaporation and by enhanced side reactions in the concentrated extract. Consequently, the odour potency of these odorants can be underestimated in comparison to those whose levels are not reduced during concentration. To clarify this point, aroma extract concentration analysis (AECA) [56] should check the results of AEDA. AECA starts with GC-O of the original extract from which the non-volatile components have been removed. The extract is then concentrated stepwise by distilling olf the solvent, and after each step an aliquot is analysed by GC-O [56]. 

The polymerization was also terminated with CH3OH or CH3OD in the case to detect butane. From the volatile fraction distilled out from the reaction mixture on a vacuum line, low-boiling compounds were collected by redistillation and subjected to the analysis by combined gas chromatography-mass spectrometry. Butane (BuH) and monodeuterated butane, CH3CH2CH2CH2D (BuD), employed as authentic samples, were obtained by the reaction of BuLi with CH3OH and CH3OD, respectively. 

As already mentioned, it is the volatile constituents that serve to identify fruit type and variety. Broadly speaking, qualitative analysis will identify the principal substances present in the volatiles fraction as representative of a particular fruit type, but it is the relative proportions of these substances that will reflect the variety. Alcohols, volatile acids, esters, carbonyl compounds, and low-boiling hydrocarbons are the principal groups represented. Analysis by GC-MS (gas chromatography coupled with mass spectroscopy) can be used to provide quantification and identification of the various constituents. 

The analysis of aroma compounds starts with the isolation of the volatile fraction from the food. Techniques used in the preparation of flavor extracts from foods have recently been reviewed [7-9], The most important task in the choice of the isolation procedure is to test whether the flavor of the extract is identical or at least similar to the flavor of the food itself. This has to be checked by a sensory evaluation of the food extract (e.g., after dilution with an appropriate medium like water or oil) before a time consuming chemical analysis is performed. 

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... 

The composition of the volatile fraction of bread depends on the bread ingredients, the conditions of dough fermentation and the baking process. This fraction contributes significantly to the desirable flavors of the crust and the crumb. For this reason, the volatile fraction of different bread types has been studied by several authors. Within the more than 280 compounds that have been identified in the volatile fraction of wheat bread, only a relative small number are responsible for the different notes in the aroma profiles of the crust and the crumb. These compounds can be considered as character impact compounds. Approaches to find out the relevant aroma compounds in bread flavors using model systems and the odor unit concept are emphasized in this review. A new technique denominated "aroma extract dilution analysis" was developed based on the odor unit concept and GC-effluent sniffing. It allows the assessment of the relative importance of the aroma compounds of an extract. The application of this technique to extracts of the crust of both wheat and rye breads and to the crumb of wheat bread is discussed. 

Fennel oleoresin is prepared by solvent extraction of whole seeds and normally contains a volatile oil of 50% or a guaranteed content in the range of 52-58%. Only small quantities are produced for specific uses as it is not a substitute for fennel oil. Chemical analysis by Barazani et al. (2002) of the volatile fraction of oleoresins from fruits of seven natural populations of F. vulgare var. vulgare (bitter fennel) from the wild and after cultivation indicated the presence of two groups of populations. Chemotypic differentiation (relative contents of estragole and trans-anethole) or phenotypic plasticity increases within-species chemical variability, but the specific ecological roles of these essential oils remain to be uncovered. 

Most oils contain low levels of saturated and unsaturated hydrocarbons. In olive oil, the unsaturated hydrocarbon squalene can constitute up to 40% of the unsaponifiable fraction (Boskou, 1996). Other hydrocarbons commonly present in olive oil are straight chain alkanes and alkenes with 13 to 35 carbon atoms, along with very low amounts of branched chain hydrocarbons. Variations are found between different olive varieties but the main hydrocarbons are those with 23, 25, 27 and 29 carbon atoms (Guinda et al., 1996). Olive oil can clearly be differentiated from other vegetable oils on the basis of hydrocarbon components, and levels of 2.6% crude rapeseed oil or crude sunflower oil can be detected by hydrocarbon analysis (Webster et al., 1999). Terpenes have been identified in the volatile fraction of crude sunflower oil (Bocci and Frega, 1996). 

Bocci, F. and Frega, N. (1996) Analysis of the volatile fraction from sunflower oil extracted under pressure. J. Amer. Oil Chem. Soc., 73(6), 713-716. 

Fusel alcohols (1-propanol, 2-methyl-1-propanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 2-phenyl-ethanol) were actually among the first aroma constituents studied, as early gas chromatographic research had indicated, erroneously, that these compounds represented the predominant volatile fraction in wines (28). Yeast-specific fusel alcohol production has been studied by a number of researchers (31,33,37-39), all of whom found production differences among yeast strains. Unfortunately yeast strains have not usually been replicated among studies an exception is the work of Delteil and Jarry (57) and Kunkee and Vilas (39). Their results for the fiisel alcohol isobutanol (2-methyl-1-propanol) are shown in Table I. Soufleros and Bertrand (55) studied fifty different yeast strains unfortunately their data do not allow for statistical analysis. Mateo and coworkers (38) examined ten... 

Attempts have also been made to describe the total structures of asphaltenes (Figure 1) in accordance with NMR data and results of spectroscopic and analytical techniques, and it is difficult to visualize these postulated structures as part of the asphaltene molecule. The fact is that all methods employed for structural analysis involve, at some stage or another, assumptions that, although based on data concerning the more volatile fractions of petroleum, are of questionable validity when applied to asphaltenes. 

By using aroma extract dilution analysis (AEDA) of the volatile fractions of fresh and stored butter oil, Widder et al. (29) determined diacetyl, butanoic acid, 8-octalactone, skatole, 8-decalactone, cw-6-dodeceno-8-decalactone, l-octen-3-one, and l-hexen-3-one as potent contributors to the flavor of butter oil. The concentration of l-octen-3-one, trani-2-nonenal, and i-l,5-octadien-3-one increased during the storage of the butter oil at room temperature. 

The information obtained from high-resolution GC analysis of the volatile fraction of essential oils must be sufficient to determine whether the product is genuine or not. If the product is adulterated, the kind and level of adulteration must be detected. Therefore a selective and accurate separation is absolutely necessary in the case of industrial analysis. On the other hand, GC sometimes permits the separation and further identification of some components of the nonvolatile residue as well. 

The measurement of the volatile fraction is very close and will become a routine method within the next few years. If a reasonable total DOC method is developed, the next project will be the qualitative and quantitative analysis of the compounds making up the DOC, and in this work both gas and liquid chromatography will play a large role. 

Dennison JE, Andersen ME, Clewell HJ, Yang RSH. Development of a physiologically based pharmacokinetic model for volatile fractions of gasoline using chemical lumping analysis. Environ Sci Technol 2004 38 5674-81. 

In numerous studies the volatile fractions of food have been analysed to identify their components. Due to the progress in instrumental analysis, particularly gas chromatography (GC) and mass spectrometry (MS), about 7600 different volatile substances have been identified in more than 400 food products up to 2004 [1]. 

Extraction of Essential Oils from Plants. Essential oils are aromatic substances widely used in the perfume industry, the pharmaceutical sector, and the food and human nutrition field. They are mixtures of more than 200 compounds that can be grouped basically into two fractions a volatile fraction, which constitutes 90-95% of the whole oil, and a nonvolatile residue, which constitutes the remaining 5-10%. The isolation, concentration, and purification of essential oils have been important processes for many years, as a consequence of the widespread use of these compounds. The common methods used are mainly based on solvent extraction and steam distillation. SFE has been used for the extraction of essential oils from plants, in an attempt to avoid the drawbacks linked to conventional techniques (57). Such is the case with the extraction of flavor and fragrance compounds, such as those from rose (58), rosemary (59), peppermint (60), eucalyptus (61), and guajava (62). The on-line coupling of the extraction and separation ietermi-nation steps (by SFE-GC-FID) has been proposed successfully for the analysis of herbs (63) and for vetiver essential oil (64). 

Characterization of Volatile Fraction. Volatile organic compounds found in oily wastewaters consist primarily of lower-molecular-weight aliphatic and aromatic hydrocarbons. Because of its relatively high vapor pressure, this fraction is quite often lost during analysis of oily wastes. For this reason a separate procedural step was incorporated into the overall scheme for analysis of the volatile fraction. An unfiltered sample of oily waste is used in this determination. The volatile fraction is separated from water by means of nitrogen sparging and collected in an activated carbon absorption column. The collected compounds are desorbed into carbon disulfide and analyzed by GC. 

The analysis of separated volatile fraction can be carried out using a number of gas chromatographic columns and conditions including those described in the Standard Test Method ANSI/ASTM D 2267-68 (3). The following conditions were used by us in the laboratory studies GC column, 6% OV 101 on 100-120 mesh Chromosorb G-HP, 5 ft X i in-stainless steel column temperature, 1.5 min hold at 60°C, temperature programmed to 105 °C at 10°C/min detector, hydrogen flame ionization. 

A study to determine the absolute content of the volatile component of C. arietinum was conducted after the pod borer (H. armigera) was shown to be attracted to chickpea seed volatiles [14, 88]. GC-MS analysis of headspace material was collected from ground C. arietinum and identified 132 compounds from mass spectrum analysis retention times or Kovats indices (Table 1) along with a further 22 compounds which are not included here because their identities could not be confirmed [89]. The most abundant components were aliphatic hydrocarbons but the next most abundant class was the terpenoids constituting approximately 35% of the volatile fractions of the floured seed. The most abundant compound of all was a-pinene which comprised 12.6% of the total mass of volatile compound. The source of the many aliphatic hydrocarbons in this... 

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