Reduction of toxicologically relevant styrene in wheat beer using specially produced wheat and barley malts

摘要

2-Methoxy-4-vinylphenol and 4-vinylphenol are important odorants in wheat beer, which are mainly enzymatically formed by decarboxylation during fermentation with the top fermenting yeast Saccharomyces cerevisiae from their respective precursors, the free phenolic acids ferulic acid and p-coumaric acid. However, also the undesired toxicologically relevant styrene can be formed from cinnamic acid by the same mechanism. Micro-brewing trials with specially produced barley and wheat malts were performed, and the concentrations of the free phenolic acids (precursors) and the corresponding vinyl aromatics were quantitated in the malts and the intermediates of beer production (unboiled wort, cast wort, and green beer) using stable isotopically labelled internal standards. Thereby, 100% wheat or barley malts produced with either high or low malting parameters (steeping degree, germination temperature, and germination time) were used for brewing. Furthermore, the influence of two different yeasts, Saccharomyces cerevisiae strain W68 (top fermenting) and Saccharomyces carlsbergensis strain W34/78 (bottom fermenting), on the amounts of the phenolic acids and the corresponding vinyl aromatics was investigated. Results indicated that modifications in barley malting parameters did not have a mitigating influence on the styrene concentration in beer. However, using wheat malt produced with low malting parameters for brewing revealed a reduced styrene amount by about 30% compared to the brew produced with wheat malt obtained by high malting parameters. In addition, the lowered styrene beer did still fulfil the consumer's expectation in regard to its overall aroma.