Fast Determination of Iso-α-Acids in Untreated Beer Samples with Specific Separation into cis- and trans-Isomers

Abstract

Bitterness of beer is commonly expressed as a value of bitterness units. The value reflects a numerical sum parameter derived by an unspecific, empirical, and spectrophotometric method. Unfortunately, non-bitter components are also detected and adulterate the bitterness result. As percentages of non-bitter substances differ in individual beers, a sole measurement of the pure concentration of iso-α-Acids would offer precise and comparable information about the genuine bitterness. Recent investigations have shown that each individual iso-α-acid variant proposes different contributions to beer taste and foam stability. Furthermore, trans-isomers were found to be significantly less stable than cis-isomers. As the degradation of iso-α-acid sensitively influences the durability of important beer attributes, avoiding the usage of less stable iso-α-acid and trans-isomer variants during beer brewing is beneficial. HPLC represents the only analytical method that is used for specific determination and quantitation of iso-α-acids in beer. Most of the commonly used HPLC applications provide a separation of all major iso-α-acids, but not into their cis- and trans-isomers. The application shown here is an automated online SPE-UHPLC method that provides the specific determination and quantitation of all cis- and trans-isomer variants of iso-α-acids that are present in beer.