P-6
Beer photooxidation creates three 3-methyl-2-butene-1-thiol related lightstruck aroma compounds
Presenter: Lance Lusk, Miller Brewing Company, Milwaukee, WI
Co-Authors: Aki Murakami, Miller Brewing Company, Milwaukee, WI; Lawrence Nielsen, Microanalytics, Round Rock, TX; and Susan Kay and David Ryder, Miller Brewing Company, Milwaukee, WI

Beer photooxidation (lightstruck reaction) creates the well-known intensely flavor-active compound 3-methyl-2-butene-1-thiol (3M2B1T). The sensory threshold for 3M2B1T is 1.25 to 4.4 ng/L in beer. The chemistry of the formation of 3M2B1T is known. The pathway involves photo-degradation of isoalpha-acids to form 3-methyl-2-butenyl radicals, which in turn combine with sulfydryl radicals produced from the photo-degradation of a sulfur-containing source such as amino acids. Using solid-phase microextraction and GC-olfactometry, we discovered two previously unidentified compounds of the 3M2B1T family in lightstruck beer. The aromas of the two compounds are indistinguishable from the "skunky" or "foxy" aroma used to describe 3M2B1T. One of the two compounds was tentatively identified by mass spectroscopy as methyl (3-methyl-2-butenyl)-disulfide. The major ion fragments of the other compound have been identified (m/z 41, 69, 101, and 115) but the compound structure has not been elucidated. This study contributes to the understanding of beer photooxidation, showing that three compounds rather than one are responsible for beer's lightstruck aroma.

Lance Lusk is a principal scientist at the Miller Brewing Company. He joined Miller in 1980 and has regularly published in the area of beer foam chemistry. Some of his other interests include hops, beer flavor, and flavor stability. He is a member of the American Society of Brewing Chemists, American Chemical Society, and The Protein Society. In 1996, Mr. Lusk was presented the American Society of Brewing Chemists' Eric Kneen Memorial Award for excellence in scientific publication. He studied biology at the University of Chicago and biochemistry at Roosevelt University (Chicago, IL), where he received A.B. and M.S. degrees, respectively.