Development and Validation of a HS-SPME-GC-SIM-MS Multi-Method Targeting Hop-Derived Esters in Beer

Hop-derived esters contribute to beer flavor and changes in the ester spectrum are believed to be an important driver in the flavor–instability of hoppy beers. To date, there exists no published method that enables reliable quantification of hop-derived esters in beer. As the availability of such a method is vital to enlarge the understanding of beer flavor stability, the current article is concerned with the development, validation, and application of a application of a headspace solid phase microextraction gas chromatography selected ion monitoring mass spectrometry (HS-SPME-GC-SIM-MS) methodology based methodology for quantification of 16 hop-derived esters in beer. The validation data shows that choosing suitable HS-SPME-GC-SIM-MS conditions enabled reliable quantification of esters across a range of 1–200 µg/L, with calculated limits of quantification being well below 1 µg/L. Spiking experiments using terpenes and terpenoids evidenced method robustness, most importantly when two commercially available stable isotope labeled internal standards (geranyl acetate and ¹³C-methyl octanoate) were used. Application to beer samples indicated that beers brewed with different qualities/quantities of hops and differing in freshness could be well differentiated by HS-SPME-GC-SIM-MS analysis of their ester profile. Supplemental data for this article is available online at at https://doi.org/10.1080/03610470.2021.1994814 .

酒花衍生酯类（hop-derived esters）对啤酒风味具有重要贡献，而酯类谱图的变化被认为是酒花风味啤酒出现风味不稳定现象的关键诱因。截至目前，尚无已发表的方法可对啤酒中的酒花衍生酯类进行可靠定量分析。鉴于此类方法的建立对于深化人们对啤酒风味稳定性的理解至关重要，本文旨在开发、验证并应用一种基于顶空固相微萃取-气相色谱-选择离子监测质谱（headspace solid phase microextraction gas chromatography selected ion monitoring mass spectrometry, HS-SPME-GC-SIM-MS）的分析方法，用于定量啤酒中的16种酒花衍生酯类。验证数据表明，通过优化HS-SPME-GC-SIM-MS分析条件，可在1~200 μg/L的浓度范围内实现酯类的可靠定量，其定量限（limits of quantification）经计算远低于1 μg/L。采用萜类与萜类化合物开展加标回收实验（spiking experiments）证实了该方法的稳健性（method robustness），尤其是在使用两种商用稳定同位素标记内标（stable isotope labeled internal standards）：乙酸香叶酯（geranyl acetate）和¹³C-辛酸甲酯（¹³C-methyl octanoate）时效果尤为显著。将该方法应用于啤酒样品分析后发现，通过酯类谱图的HS-SPME-GC-SIM-MS分析，可以有效区分使用不同品质/用量酒花酿造且新鲜度各异的啤酒样品。本文的补充数据可通过以下链接在线获取：https://doi.org/10.1080/03610470.2021.1994814。