Solid-phase microextraction method development for headspace analysis of volatile flavor compounds

Solid-phase microextraction (SPME) fibers were evaluated for their ability to adsorb volatile flavor compounds under various conditions with coffee an d aqueous flavored solutions. Experiments comparing different fibers showed that poly(dimethylsiloxane)/divinylbenzene had the highest overall sensiti vity. Carboxen/poly(dimethylsiloxane) was the most sensitive to small molec ules and acids. As the concentrations of compounds increased, the quantitat ive linear range was exceeded as shown by competition effects with 2-isobut yl-3-methoxypyrazine at concentrations above 1 ppm. A method based on a sho rt-time sampling of the headspace (1 min) was shown to better represent the equilibrium headspace concentration. Analysis of coffee brew with a 1-min headspace adsorption time was verified to be within the linear range for mo st compounds and thus appropriate for relative headspace quantification. Ab solute quantification of volatiles, using isotope dilution assays (IDA), is not subject to biases caused by excess compound concentrations or complex matrices. The degradation of coffee aroma volatiles during storage was foll owed by relative headspace measurements and absolute quantifications. Both methods gave similar values for 3-methylbutanal, 4-ethylguaiacol, and 2,3-p entanedione. Acetic acid, however, gave higher values during storage upon r elative headspace measurements due to concurrent pH decreases that were not seen with IDA.