First identification of the odour‐active unsaturated aliphatic acid (E)‐4‐methyl‐3‐hexenoic acid in yuzu (Citrus junos Sieb. ex Tanaka)

Abstract

We have investigated the aroma of yuzu (Citrus junos Sieb. ex Tanaka). Application of the aroma extract dilution analysis technique allowed us to determine a sequence of the odour‐active compounds in yuzu volatile oil. In this study, we confirmed the presence of an unknown odorant that possesses a sweaty odour and a relatively high flavour dilution factor. In order to identify the unknown compound, the concentrated volatile acid fraction of yuzu volatile oil was obtained, using an enrichment procedure consisting of the combination of the sub‐extraction of an acidic component with a basic aqueous solution and subsequent affinity chromatography with an Oasis MAX cartridge. Gas chromatography–olfactometry and multi‐dimensional gas chromatography–mass spectrometry analyses revealed that the unknown compound was (E)‐4‐methyl‐3‐hexenoic acid [(E)‐4M3H]. (E)‐4M3H was identified for the first time as an odour‐active unsaturated aliphatic acid in yuzu. Additionally, both (Z)‐ and (E)‐4M3H were stereoselectively synthesised over two steps comprised of the iron‐catalysed carbometalations of homopropargylic alcohols with Grignard reagents, followed by oxidation. On the basis of sensory evaluation, the orthonasal odour detection threshold of the (E)‐isomer was 10‐fold to 100‐fold lower than that of the (Z)‐isomer. Copyright © 2012 John Wiley & Sons, Ltd.

Identification of the Compounds Responsible for the Sweat-Like Odor in Hop (Humulus lupulus L.) Volatile Oil

“…Based on this result, A and B were predicted to be volatile acids according to the literature (Miyazato et al, 2013), while C and D were empirically predicted to be volatile ketones or esters according to the literature (Miyazato, Hashimoto, & Hayashi, 2007). e) Estimated by AEDA: 2 n (n, value of dilution degree).…”

“…(E)-4-Methyl-3-hexenoic acid was identified for the first time in hops. Very recently, (E)-4-methyl-3-hexenoic acid has been determined to be an odor-active compound in some natural sources, such as yuzu (Miyazato et al, 2013) and kabosu (Tomiyama, Aoki, Oikawa, Sakurai, Kasahara, & Kawakami, 2012). Further, Takeuchi, Hasegawa, Ishida, and Kashiwagi (2012) have reported (E)-4-methyl-3-hexenoic acid as the key odorous component responsible for the malodor in laundry.…”

“…Other than brief descriptions (Steinhaus & Schieberle, 2000;Lermusieau et al, 2001;Steinhaus et al, 2007), there are no detailed reports regarding the aroma components responsible for the sweat-like odor in hops, most of which may contribute to the overall aroma. Based on our previous study (Miyazato, Hashimoto, & Hayashi, 2013), we predict that the sweat-like odor perceived in hop volatile oil might be associated with volatile carboxylic acids.…”

“…(E)-4-Methyl-3-hexenoic acid was synthesized stereoselectively in two steps, according to the literature (Miyazato et al, 2013). Methyl (E)-4-methyl-3-hexenoate was synthesized via boron trifluoride-catalyzed methyl esterification of (E)-4-methyl-3-hexenoic acid starting from (E)-4-methyl-3-hexen-1-ol.…”

“…Acetone, pentane, 2-propanol, hexane, ethyl acetate, diethyl ether, hydrochloric acid (35%), triethylamine, sodium hydrogen carbonate, anhydrous sodium sulfate, anhydrous magnesium sulfate, and silica gel (Ultra Pure Silica Gel 230-400 mesh, SiliCycle Inc., Quebec City, Canada) were purchased from Nacalai Tesque (Kyoto, Japan). Jones reagent was prepared according to the literature (Miyazato et al, 2013).…”