Stale aldehyde analysis by in-solution PFBHA derivatization and SPME-GC-ECD

Analytical Session
Qin Zhou, Oregon State University, Corvallis, OR 97331, USA
Co-author(s): Michael Qian, Oregon State University, Corvallis, OR, USA

ABSTRACT: Aldehydes are important flavor compounds that are widely distributed in every food system, contributing positively or negatively depending on their concentration and the food system. Stale aldehydes, including Strecker and saturated and unsaturated aldehydes with chain lengths of C8–C10, are generated from degradation of amino acids and oxidation of lipids, which are typically associated with beer oxidation during storage. Some of these compounds, such as (E)-2-nonenal and (E,Z)-2,6-nonadienal, can cause a “sawdust” off-flavor in beer at concentrations as low as 0.1–0.3 ng/mL–l (ppb). However, the aroma contribution of these aldehydes to beer flavor is poorly understood due to the technical difficulty in measuring these compounds at such low concentrations. In this study, a sensitive method for the determination of stale aldehydes has been developed. Aldehydes were derivatized with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) in solution at 50°C for 40 min. The corresponding oximes were extracted using DVB-PDMS solid phase microextraction (SPME) and analyzed by gas chromatography–electron capture detector. The limit of quantification for most compounds was as low as 0.1 µg/L (0.1 ppb), and the linearity held at least up to 50 µg/L with R2 in the range of 0.991 to 0.999. The method was successfully applied to analyze stale aldehydes in beer samples.

Qin Zhou received a B.S. degree in chemistry from Wuhan University in China in 2006, and her M.S. degree in fermentation engineering from China National Research Institute of Food and Fermentation Industries in 2009. In 2010, she began pursuing a Ph.D. degree in Michael Qian’s flavor chemistry lab at Oregon State University in the Food Science and Technology Department. Her work focuses on the flavor chemistry of alcoholic beverages, including beer and wine.