Examination of Beer Carbonyls as Their Oximes by Gas Chromatography-Mass Spectrometry

Abstract

Bisulfite addition complexes were utilized in a method devised to obtain extracts suitable for the relatively rapid isolation and identification of beer carbonyl components as their oxime derivatives by combined gas chromatography-mass spectrometry. Analysis of a commercial lager revealed that the aldoximes in the extracts included alkanals, 3-hydroxyalkanals, and 2-methyl-2-alkenals. Hexenal and nonenal were determined to be present in beer as cis-3 isomers. Under the acid conditions used in other analyses, these may isomerize to trans-2-alkenals. The cis-3-alkenals observed are expected products of the oxidative degradation of linoleic and linolenic acids. The 2-methyl-2-alkenals may be derived from aldol condensations involving propanal, which itself is an oxidative cleavage product of linolenic acid. A scheme is proposed for the formation of the identified beer carbonyls from linoleic and linolenic acids derived from malt.

• Analytical method
• Beer
• Bisulfite
• Oximes
• Unsaturated aldehydes