Determination of isoxanthohumol, xanthohumol, alpha and beta bitter acids, and trans- and cis-iso-alpha-acids in beer using HPLC with UV and electrochemical detection

Analytical Session
David H Thomas, Thermo Fisher Scientific, Chelmsford, MA, USA
Co-author(s): Paul Ullucci and Ian Acworth, Thermo Fisher Scientific, Chelmsford, MA, USA

ABSTRACT: Beer is the most widely consumed alcoholic beverage in the world and the third most popular drink after water and tea. Beer is brewed from four basic ingredients: water, a starch source (e.g., malted barley), brewer’s yeast, and a flavoring agent such as hops. Many varieties of beer result from differences in these ingredients, the additives used, and the brewing process followed. While there are many different types of beer, all have one characteristic in common—bitterness. Hop or hop extracts are added during the boiling of the wort. During this time the virtually insoluble alpha-acids (humulones) are isomerized into the more soluble iso-alpha-acids, the main bittering substances in beer. In addition, beta-acids (lupulones) also add to the bitterness in beer. The analysis of hop acids in hops and beer is important for quality control of the beverage. Many HPLC methods have been applied to the determination of bitter acids in beer. HPLC techniques using UV detection typically require a concentration step in the analysis to be able to determine low levels of bitter acids. Application of HPLC with electrochemical detection allows the determination of bitter acids even in light beers without the need for preconcentration. Chromatographic separation was performed on a Dionex Acclaim C30 column (3 µm, 3.0 × 150 mm) at 35°C with gradient elution and simultaneous UV (270 nm) and EC detection (500 and 800 mV). Sample preparation involved extraction with acidified acetonitrile and centrifugation. All calibration curves showed good linear regression (r2 > 0.996). RSDs over a 20-hr run are as follows: isoxanthohumol and xantholhumol, 1.2%; alpha and beta bitter acids, 2.5%; and trans- and cis-iso-alpha-acids, 2.4%.

Dave Thomas received a Ph.D. degree in analytical chemistry from the University of Nebraska-Lincoln in 1994 for his work developing high-performance immunoaffinity chromatography. In post-doctoral appointments at Midwest Research Institute-California Operations and Sandia National Laboratories, he worked to implement HPIAC and HPLC approaches on miniaturized electrochromatographic separation and analysis platforms. Later, he spent several years developing a variety of IC, HPLC, and LC/MS applications at Dionex Corporation and Thermo Fisher Scientific, where he also served as manager of the HPLC and LCMS applications laboratory. After a few years in vaccine analytical development at Wyeth and Pfizer, Dave returned to Thermo Fisher Scientific, where he continues to develop applications for HPLC with charged aerosol and electrochemical detection.