Volatile metabolites

Abstract

Volatile organic compounds (volatiles) comprise a chemically diverse class of low molecular weight organic compounds having an appreciable vapor pressure under ambient conditions. Volatiles produced by plants attract pollinators and seed dispersers, and provide defense against pests and pathogens. For insects, volatiles may act as pheromones directing social behavior or as cues for finding hosts or prey. For humans, volatiles are important as flavorants and as possible disease biomarkers. The marine environment is also a major source of halogenated and sulfur-containing volatiles which participate in the global cycling of these elements. While volatile analysis commonly measures a rather restricted set of analytes, the diverse and extreme physical properties of volatiles provide unique analytical challenges. Volatiles constitute only a small proportion of the total number of metabolites produced by living organisms, however, because of their roles as signaling molecules (semiochemicals) both within and between organisms, accurately measuring and determining the roles of these compounds is crucial to an integrated understanding of living systems. This review summarizes recent developments in volatile research from a metabolomics perspective with a focus on the role of recent technical innovation in developing new areas of volatile research and expanding the range of ecological interactions which may be mediated by volatile organic metabolites.

Figure 1.

Chemical structures of some plant, microbial and mammalian derived volatiles.

Figure 2.

GC-MS (TIC) chromatograms of apple fruit volatiles showing the dependency of the volatile profile upon the methodology used, and the chemical simplicity and selectivity of a typical headspace profile. A complete chromatogram of the diethyl ether extract of Jazz™ (‘SciFresh’) apple skin (A) showing the volatiles in the region (3–16 min), and an expansion of this volatile region (B), is compared with the headspace volatile profile obtained from a ‘Royal Gala’ x ‘Granny Smith’ apple (C). Chromatographic separations used DB5 and Carbowax GC columns to ensure the elution of high boiling components and to maximize isomeric separations respectively. Labeled peaks are butyl acetate (1), 2-methylbutyl acetate (2), hexyl acetate (3), butyl hexanoate (4), hexyl 2-methylbutanoate (5), α-farnesene (6) and internal standard (IS).

Figure 2.

GC-MS (TIC) chromatograms of apple fruit volatiles showing the dependency of the volatile profile upon the methodology used, and the chemical simplicity and selectivity of a typical headspace profile. A complete chromatogram of the diethyl ether extract of Jazz™ (‘SciFresh’) apple skin (A) showing the volatiles in the region (3–16 min), and an expansion of this volatile region (B), is compared with the headspace volatile profile obtained from a ‘Royal Gala’ x ‘Granny Smith’ apple (C). Chromatographic separations used DB5 and Carbowax GC columns to ensure the elution of high boiling components and to maximize isomeric separations respectively. Labeled peaks are butyl acetate (1), 2-methylbutyl acetate (2), hexyl acetate (3), butyl hexanoate (4), hexyl 2-methylbutanoate (5), α-farnesene (6) and internal standard (IS).