Development of preparative and analytical methods of the hop bitter acid oxide fraction and chemical properties of its components

The bitter acids in hops (Humulus lupulus L.) and beer, such as α-, β-, and iso-α-acids, are known to affect beer quality and display various physiological effects. However, these compounds readily oxidize, and the effect of the oxides on the properties of beer or their potential health benefits are not well understood. In this study, we developed a simple preparative method for the bitter acid oxide fraction derived from hops and designated the constituents as matured hop bitter acids (MHBA). HPLC-PDA-ESI/HRMS and MS2 revealed that MHBA are primarily composed of α-acid-derived oxides, which possess a common β-tricarbonyl moiety in their structures similar to α-, β-, and iso-α-acids. We also developed a quantitative analytical method of whole MHBA by HPLC, which showed high precision and reproducibility. Using our newly developed method, the concentration of whole MHBA in several commercial beers was evaluated. Our results will promote the study of bitter acid oxides.

啤酒花（Humulus lupulus L.）及啤酒中含有的苦味酸类物质（如α-酸、β-酸与异α-酸），已知可影响啤酒品质并展现出多种生理活性。然而，此类化合物极易发生氧化反应，目前对于其氧化物对啤酒品质的影响，以及这类氧化物潜在的健康益处，尚未形成充分的研究认知。本研究建立了一种从啤酒花中提取苦味酸氧化物组分的简易制备方法，并将该组分的构成成分命名为熟化啤酒花苦味酸（matured hop bitter acids，MHBA）。通过高效液相色谱-光电二极管阵列检测-电喷雾电离高分辨质谱（HPLC-PDA-ESI/HRMS）及二级质谱（MS²）分析，证实MHBA主要由α-酸氧化产物构成，其结构中含有与α-酸、β-酸及异α-酸相似的共同β-三羰基结构单元。本研究同时开发了针对总MHBA的高效液相色谱定量分析方法，该方法具备优异的精密度与重现性。利用该新建方法，本研究对多款市售啤酒中的总MHBA含量进行了测定分析。本研究结果将有力推动苦味酸氧化物相关领域的研究进展。