Evaluation of PDMS-based Extraction Techniques and GC-TOFMS for the Analysis of Off-flavor Chemicals in Beer (1). R. T. Marsili (2), L. C. Laskonis, and C. Kenaan, Marsili Consulting Group, Rockford College, Rockford, IL. (1) This work was presented as a poster at the World Grains Summit: Foods and Beverages, September 2006, San Francisco, CA. (2) Corresponding author. Marsili Consulting Group, Rockford College, Starr Science Bldg., Rm. 120, 5050 E. State St., Rockford, IL 61108. E-mail: <rmarsili@marsiliconsulting.com>; Phone: +1.815.289.0303; Fax: +1.815.544.9203. J. Am. Soc. Brew. Chem. 65(3):129-137, 2007.

Various formats employing polydimethylsiloxane (PDMS) as an extraction medium prior to gas chromatography/time-of-flight mass spectrometry (GC-TOFMS) analysis were investigated to measure off-flavors in aged beer. The techniques included stir bar sorptive extraction (SBSE), headspace sorptive extraction (HSSE), purge and trap, and closed-loop stripping (CLS). Although all PDMS extraction methods worked well, SBSE appeared to provide the most accurate quantitation and was capable of detecting the most odor-active compounds. The peak deconvolution capability of the Leco Pegasus TOFMS was critical to the detection and accurate quantitation of key off-flavor chemicals. Compared with fresh control beer, increases in furfural; furfuryl ethyl ether; furyl hydroxymethyl ketone; 2,4-dodeca­dienal, (E,E)-; benzeneacetic acid ethyl ester; beta-damascenone; and 3-pyri­dinecarboxylic acid ethyl ester (also known as nicotinic acid ethyl ester) were observed in beer samples incubated for 12 weeks at 30°C, and increases in dimethyl disulfide, dimethyltrisulfide, and benzeneacetaldehyde occurred in beer samples exposed to sunlight for 8 hr. Keywords: Beer, Gas chromatography/time-of-flight mass spectrometry (GC-TOFMS), Headspace sorptive extraction (HSSE), Off-flavors, Poly­dimethylsiloxane (PDMS), Stir bar sorptive extraction (SBSE)