Perceptual Characterization and Analysis of Aroma Mixtures Using Gas Chromatography Recomposition-Olfactometry

This paper describes the design of a new instrumental technique, Gas Chromatography Recomposition-Olfactometry (GC-R), that adapts the reconstitution technique used in flavor chemistry studies by extracting volatiles from a sample by headspace solid-phase microextraction (SPME), separating the extract on a capillary GC column, and recombining individual compounds selectively as they elute off of the column into a mixture for sensory analysis (Figure 1). Using the chromatogram of a mixture as a map, the GC-R instrument allows the operator to “cut apart" and recombine the components of the mixture at will, selecting compounds, peaks, or sections based on retention time to include or exclude in a reconstitution for sensory analysis. Selective recombination is accomplished with the installation of a Deans Switch directly in-line with the column, which directs compounds either to waste or to a cryotrap at the operator's discretion. This enables the creation of, for example, aroma reconstitutions incorporating all of the volatiles in a sample, including instrumentally undetectable compounds as well those present at concentrations below sensory thresholds, thus correcting for the “reconstitution discrepancy" sometimes noted in flavor chemistry studies. Using only flowering lavender (Lavandula angustifola ‘Hidcote Blue’) as a source for volatiles, we used the instrument to build mixtures of subsets of lavender volatiles in-instrument and characterized their aroma qualities with a sensory panel. We showed evidence of additive, masking, and synergistic effects in these mixtures and of “lavender' aroma character as an emergent property of specific mixtures. This was accomplished without the need for chemical standards, reductive aroma models, or calculation of Odor Activity Values, and is broadly applicable to any aroma or flavor.本论文介绍了一种新型仪器技术——气相色谱重组-嗅觉测定法（Gas Chromatography Recomposition-Olfactometry, GC-R）的设计方案。该技术借鉴风味化学研究中的重组技术流程：通过顶空固相微萃取（headspace solid-phase microextraction, SPME）从样品中提取挥发性组分，经毛细管气相色谱柱对提取物完成分离，并在组分从色谱柱洗脱时，选择性地将单个化合物重新混合为可用于感官分析的混合样品（如图1所示）。该GC-R仪器以混合物的色谱图作为定位图谱，可让操作人员按需‘拆解’并重组混合物组分，根据保留时间选择纳入或排除特定化合物、色谱峰或区段，以制备用于感官分析的重组样品。选择性重组可通过在色谱柱直连管路中加装迪恩斯切换阀（Deans Switch）实现，操作人员可自主控制将化合物导入废液流或冷阱（cryotrap）。这一设计能够制备涵盖样品中全部挥发性组分的香气重组物，其中既包含仪器无法检出的组分，也包含浓度低于感官阈值的组分，从而修正了风味化学研究中偶尔出现的‘重组偏差’（reconstitution discrepancy）问题。本研究仅以狭叶薰衣草（Lavandula angustifolia ‘Hidcote Blue’）作为挥发性组分的唯一来源，利用该仪器在仪器内部制备薰衣草挥发性组分的子集混合物，并通过感官评价小组对其香气品质进行表征。研究证实了这些混合物中存在加和、掩蔽与协同效应，且‘薰衣草’香气特征是特定混合物的涌现属性。本研究无需依赖化学标准品、还原型香气模型或气味活性值（Odor Activity Values）的计算，且可广泛应用于各类香气或风味体系。