Food Chemistry and Molecular Sensory Science, Technische Universitat Munchen, Lise-Meitner Strasse 34, Freising, Germany.
J Agric Food Chem. 2009 Aug 26;57(16):7480-9. doi: 10.1021/jf901759y.
Thermal treatment of the hop beta-acid colupulone under wort boiling conditions, followed by LC-TOF-MS and 1D/2D NMR spectroscopy, revealed cohulupone, hulupinic acid, nortricyclocolupone, two tricyclocolupone epimers, two dehydrotricyclocolupone epimers, two hydroxytricyclocolupone epimers, and two hydroperoxytricyclocolupone epimers as the major bitter-tasting beta-acid transformation products. Among these compounds, the chemical structures of the hydroxy- as well as the hydroperoxytricyclocolupone epimers have not previously been confirmed by 1D/2D NMR experiments. Depending on their chemical structure, these compounds showed rather low recognition thresholds ranging from 7.9 to 90.3 micromol/L. The lowest thresholds of 7.9 and 14.7 micromol/L were found for cohulupone, imparting a short-lasting, iso-alpha-acid-like bitter impression, and for hydroxytricyclocolupone, exhibiting a long-lasting, lingering, and harsh bitterness perceived on the posterior tongue and throat. Furthermore, HPLC-ESI-MS/MS analysis allowed for the first time a simultaneous detection and quantitation of these bitter-tasting beta-acid transformation products in a range of commercial beer samples without any sample cleanup. Depending on the type of beer, these studies revealed remarkable differences in the concentrations of the individual beta-acid transformation products.
在麦汁煮沸条件下对啤酒花β酸律草酮进行热处理，然后通过 LC-TOF-MS 和 1D/2D NMR 光谱分析，发现了律草酮、律草酮酸、诺特环律草酮、两个三环律草酮差向异构体、两个脱氢三环律草酮差向异构体、两个羟基三环律草酮差向异构体和两个过氧羟基三环律草酮差向异构体，这些是主要的苦味β酸转化产物。在这些化合物中，羟基和过氧羟基三环律草酮差向异构体的化学结构以前从未通过 1D/2D NMR 实验得到证实。根据其化学结构，这些化合物的识别阈值相当低，范围从 7.9 到 90.3 微摩尔/升。 cohulupone 的识别阈值最低，为 7.9 和 14.7 微摩尔/升，它赋予了短暂的、类似异-α-酸的苦味印象，而羟基三环律草酮的识别阈值最低，为 14.7 微摩尔/升，具有持久、残留和喉咙后部的强烈苦味。此外，HPLC-ESI-MS/MS 分析首次允许在无需任何样品净化的情况下，同时检测和定量范围商业啤酒样品中的这些苦味β酸转化产物。根据啤酒的类型，这些研究显示出单个β酸转化产物的浓度存在显著差异。
