60. Chasing staling aldehydes—A unique application of HS-SPME-GC-MS/MS in brewing

Jörg Maxminer (1), Johanna Koserske (1), Nils Rettberg (1), Sarah Thörner (1); (1) Research and Teaching Institute for Brewing in Berlin (VLB), Berlin, Germany

Technical Session 17: Beer Aging
Tuesday, August 16  •  3:30–5:15 p.m.
Plaza Building, Concourse Level, Governor’s Square 14

The aroma of beer is a major quality characteristic that is commonly described as a complicated puzzle with hundreds of pieces. Beer as manufactured is not at chemical equilibrium and undergoes complex chemical reactions during storage, which can lead to undesirable changes in sensory characteristics. This phenomenon largely remains a mystery and is a major challenge for the brewing industry in the effort to supply a consistent product to consumers. Certain aldehydes are essential for the perception of staleness and can be directly linked to undesirable sensory attributes as their concentration increases during storage. When it comes to the analysis of staling aldehydes, their volatility, reactivity, but most importantly their low concentration (µg/L to ng/L) in a complex beer matrix, has challenged brewers for decades. Doubtless, gas chromatography-mass spectrometry is a well-established tool for the analysis of staling aldehydes; however, drawbacks in selectivity and sensitivity can hinder the reliable quantification of those aldehydes related to undesirable “aged flavor.” These drawbacks might be circumvented when using headspace solid-phase microextraction combined with gas chromatography and tandem mass spectrometry (HS-SPME-GC-MS/MS), which is a new tool in brewing analysis. The performance in the sub-ppb range increases enormously using this analysis technique. The current presentation gives a detailed insight into an improved method for the analysis of staling aldehydes utilizing a HS-SPME step and on-fiber derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA). The oxime derivatives formed on the fiber are thermally disport, followed by gas chromatographic separation coupled to a GC-MS/MS. Selecting specific fragment ions within the electron ionization (EI(+)) mass spectra of these oxime derivatives as precursor ions for MS-MS fragmentation provides a suitable method for the target analysis of individual aldehydes. Employing isotope standard d5-phenylethanal as an internal standard increases the reproducibility and is a unique feature of this tandem mass spectrometry technique. In the present study, the method was verified for 15 different staling aldehydes by analyzing 4 different beer styles (alcohol-free, lager, dark and ale) fresh and after 1 and 2 weeks of storage at 40°C. Low limits of quantification (down to 25 ng/L) and a wide working range (up to 250 µg/L) could be accomplished for certain aldehydes in all 4 beer matrices. The very low standard deviations (<10%) and high linearity (R2 > 0.99) achieved for all evaluated aldehydes is a major advantage of this technique compared to any other method previously described. The above data highlight the advantages of this promising measuring technique (e.g., selectivity, sensitivity, automation) and its possibilities to gain further understanding about the complex chemistry of beer aging and in the hunt for improved flavor stability.

After receiving a Dipl.-Ing. (FH) degree in beverage technology from the University of Applied Science Wiesbaden-Geisenheim (Germany), Jörg Maxminer worked at the Karlsberg Brewery in Homburg (Germany) in the Technology and Development Department for two years. In 2011 he graduated from Heriot-Watt University Edinburgh (U.K.) with an M.S. degree in brewing and distilling. Jörg is currently working toward a Ph.D. degree at the University of Nottingham (U.K.) with a research focus on flavor stability of lager-style beers. In addition, Jörg is employed as head of the department for the central laboratory at the Research Institute for Instrumental Beer and Beverage Analysis at the Research and Teaching Institute for Brewing in Berlin (VLB) (Germany). Here he manages the standard beer analysis and is involved in different research projects with a focus on beer flavor. Aside from work, Jörg enjoys brewing his own beer and playing handball.