What Makes Yuzu Fragrant?

🍊Yuzu is a popular citrus fruit for cooking in Japan that has a characteristic flavor. Sashimi, grilled meat/fish, ramen, syabu-syabu,pickles, sweet drinks, ice cream, alcohol, everything becomes tasty! We sometimes put yuzu in the bath to enjoy its aroma.

T.Hasegawa Co., Ltd., in Japan🇯🇵 discovered Yuzunone and Yuzuol as important molecules of yuzu flavor. AEDA (Aroma Extract Dilution Analysis) is a method to detect aroma components separated by gas chromatography by sniffing with the human nose. Yuzu’s unique aroma components, which were present in very small quantities, were identified by repeated fractionation using AEDA. Since it was the unknown compound, the molecule was given a name derived from yuzu. The amounts of YUZUNONE® and YUZUOL® in peel oil were 5.5 ppm and 1.6 ppm, respectively. However, the threshold value is very low and even a small amount (10, 42 ppt) has a strong aroma. (ppt means parts per trillion.) The ratio of isomers present in nature was 1:6 for (6E,8E) and (6Z,8E).

🧪T.Hasegawa Co., Ltd. also established the commercial scale production of Yuzunone. After conversion of readily available 2-ethylfuran to the acetal compound, deprotection is carried out in acidic aqueous solution. Wittig reaction of the corresponding aldehyde affords Yuzunone; however, such aldehyde is too unstable. Alternatively, the resulting aldehyde is induced to a hydroxy sulfonate without isolation and then Wittig reaction of this compound directly afforded Yuzunone.

📖Reference

1. “Novel Character Impact Compounds in Yuzu (Citrus junos Sieb. ex Tanaka) Peel Oil” J. Agric. Food Chem. 2009, 57, 1990.

2. “天然食材中の超微量重要香気成分の研究 合成化学を通じた食品香料への応用” 化学と生物, 2016, 54, 365.

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