Lehrstuhl für Lebensmittelchemie und Molekulare Sensorik, Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt, Technische Universität München, D-85354 Freising, Germany.
Institut für Lebensmitteltechnologie und Lebensmittelchemie, Fachgebiet Brauwesen, Technische Universität Berlin, Seestraße 13, D-13353 Berlin, Germany.
J Agric Food Chem. 2020 Nov 4;68(44):12421-12432. doi: 10.1021/acs.jafc.0c04835. Epub 2020 Oct 20.
Mitigation studies on styrene in wheat beer found no correlation between the free phenolic acid contents in the processing steps and the final concentrations of the toxicologically relevant styrene and the desired aroma-active vinyl aromatics in beer, which can be explained by the presence of phenolic acid releasing enzymes that are still active after kiln-drying and by the yeast's own feruloyl esterase activity. The present study contributed to a better understanding of the coherence between the free, soluble ester-bound, and insoluble ester-bound forms of cinnamic, -coumaric, and ferulic acid during malting and mashing of barley and wheat varieties. Concentration differences in malt by factors of up to 1700 were found between the total cinnamic acid contents (an undesired precursor of the toxicologically relevant styrene) and the total contents of -coumaric and ferulic acid (both desired precursors of the aroma-active compounds 4-vinylphenol and 2-methoxy-4-vinylphenol). In grain and malt, cinnamic acid occurred predominantly in a soluble form, whereas the desired precursors were mainly insoluble ester-bound. This had a direct effect on the transfer rates from malt into wort, which were found to be >100% for cinnamic acid, revealing that a complete transfer was accompanied by an additional biosynthesis, but only <8% for the desired phenolic acids. Interestingly, in the wort, cinnamic and -coumaric acid contents were dominated by the free form, while ferulic acid was mostly still soluble ester-bound. Overall, the use of barley malts led to an introduction of cinnamic, -coumaric, and ferulic acid into the wort in a ratio of 2:14:84, and the use of wheat malt in a ratio of 1:2:97.
在小麦啤酒中对苯乙烯的缓解研究发现，加工步骤中游离酚酸含量与啤酒中有毒理学相关性的苯乙烯和所需的芳香活性乙烯基芳烃的最终浓度之间没有相关性，这可以用酚酸释放酶的存在来解释，这些酶在窑干后仍然活跃，并且酵母自身具有阿魏酰酯酶活性。本研究有助于更好地理解在大麦和小麦品种的麦芽和糖化过程中，肉桂酸、-香豆酸和阿魏酸的游离、可溶酯结合和不可溶酯结合形式之间的一致性。在麦芽中，总肉桂酸含量（有毒理学相关性的苯乙烯的不期望前体）和总-香豆酸和阿魏酸含量（两者都是芳香活性化合物 4-乙烯基苯酚和 2-甲氧基-4-乙烯基苯酚的期望前体）之间的浓度差异高达 1700 倍。在谷物和麦芽中，肉桂酸主要以可溶形式存在，而所需的前体主要是不可溶的酯结合形式。这直接影响了从麦芽向麦汁中的转移率，发现肉桂酸的转移率>100%，这表明完全转移伴随着额外的生物合成，但对于所需的酚酸，转移率<8%。有趣的是，在麦汁中，肉桂酸和-香豆酸的含量主要由游离形式决定，而阿魏酸主要仍以可溶酯结合形式存在。总的来说，使用大麦麦芽会导致麦汁中引入肉桂酸、-香豆酸和阿魏酸的比例为 2:14:84，而使用小麦麦芽的比例为 1:2:97。
