85. Update on an alternative method to measure alpha-acid utlization: Isomerized alpha-acids in beer and subsequent spectrophotometric measurement

Scott Lafontaine (1), Tom Shellhammer (1), Philip Wietstock (2); (1) Oregon State University, Corvallis, OR, U.S.A.; (2) Technische Universität Berlin, Berlin, Germany

Analytical
Poster

The method being presented was developed as an alternative approach to measure iso-alpha-acids in beer using solid-phase extraction (SPE) and subsequent spectrophotometric measurement. It was initially conceived to be a simpler alternative to the international bitterness unit (ASBC Beer 23a) and because it eliminates the use of iso-octane. However, after a second ASBC Technical Subcommittee report in 2013 the reproducibility and repeatability results of a ring study were judged to be unacceptable, and the method needed improvement. Recent changes in the elution solvent and the stationary phase during the SPE have increased the reproducibility and repeatability of the proposed method. Interestingly, the method was also expanded to include oxidized hop acids, which have been shown to contribute sensory bitterness in hop-forward beers. The updated SPE protocol was used to extract isomerized and oxidized iso-alpha-acids from 120 commercially available beers. The resulting UV absorbance for these beers were correlated to IBUs (ASBC Beer 23a ) and iso-alpha-acids by HPLC (ASBC Beer 23e), as well as sensory bitterness as perceived by a trained taste panel. These results suggest that the proposed method be considered as a potentially viable alternative approach to HPLC and the IBU for measuring isomerized and oxidized alpha-acids in beer.

In the spring of 2015, Scott Lafontaine joined Dr. Thomas Shellhammer’s laboratory at Oregon State University in the Department of Food Science and Technology to pursue a Ph.D. degree in food science. Currently, Scott’s research interests broadly revolve around hop flavor in beer. He graduated with a M.S. degree in chemistry from Oregon State University in the winter of 2015 and received his B.S. degree in both chemistry and science technology from Kean University in the spring of 2012.

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