In this study, we examined the mode of metabolism of food odorant molecules in the human nasal/oral cavity in vitro and in vivo. We selected 4 odorants, 2-furfurylthiol (2-FT), hexanal, benzyl acetate, and methyl raspberry ketone, which are potentially important for designing food flavors. In vitro metabolic assays of odorants with saliva/nasal mucus analyzed by gas chromatography mass spectrometry revealed that human saliva and nasal mucus exhibit the following 3 enzymatic activities: (i) methylation of 2-FT into furfuryl methylsulfide (FMS); (ii) reduction of hexanal into hexanol; and (iii) hydrolysis of benzyl acetate into benzyl alcohol. However, (iv) demethylation of methyl raspberry ketone was not observed. Real-time in vivo analysis using proton transfer reaction-mass spectrometry demonstrated that the application of 2-FT and hexanal through 3 different pathways via the nostril or through the mouth generated the metabolites FMS and hexanol within a few seconds. The concentration of FMS and hexanol in the exhaled air was above the perception threshold. A cross-adaptation study based on the activation pattern of human odorant receptors suggested that this metabolism affects odor perception. These results suggest that some odorants in food are metabolized in the human nasal mucus/saliva, and the resulting metabolites are perceived as part of the odor quality of the substrates. Our results help improve the understanding of the mechanism of food odor perception and may enable improved design and development of foods in relation to odor.

中文翻译：

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人鼻/口腔中异味分子的代谢会影响异味感。

在这项研究中，我们研究了体外和体内人鼻/口腔中食物气味分子的代谢模式。我们选择了4种增香剂，2-糠基硫醇（2-FT），己醛，乙酸苄酯和甲基树莓酮，这些对设计食品风味剂可能具有重要意义。气相色谱质谱法分析唾液/鼻粘液对气味的体外代谢分析显示，人唾液和鼻粘液具有以下3种酶活性：（i）2-FT甲基化为糠基甲基硫醚（FMS）；（ii）将己醛还原为己醇；（iii）将乙酸苄酯水解成苄醇。但是，没有观察到（iv）甲基覆盆子酮的去甲基化。使用质子转移反应质谱的实时体内分析表明，通过3种不同途径通过鼻孔或通过口腔应用2-FT和己醛可在几秒钟内产生代谢产物FMS和己醇。呼出空气中FMS和己醇的浓度高于感知阈值。一项基于人类气味受体激活模式的交叉适应研究表明，这种代谢会影响气味感知。这些结果表明，食物中的某些气味物质在人的鼻粘液/唾液中被代谢，并且所产生的代谢产物被视为底物气味质量的一部分。我们的结果有助于增进对食物异味感知机制的理解，并可能改善与气味有关的食物的设计和开发。