Exploration of an odorous aldehydes and ketones produced by Uroglena americana using high resolution mass spectrometry, GC-Olfactometry, and multivariate analysis

Abstract

Off-flavor events in tap water have been reported from various regions of Japan. Fishy smell is the second most common off-flavor in Japan and Uroglena americana (U. americana) is known to be a major contributor to the smell. However, the causative compound of the smell it produces still remains unrevealed to the best of our knowledge. In this study, an exploration of odorous aldehydes and ketones originating from U. americana was performed with a view to discovering a possible candidate substance of causative compounds. Environmental samples containing U. americana colony and cultured media with U. americana were analyzed with two high resolution mass spectrometers, one of them is coupled with liquid chromatography (LC-HRMS), and the other is with gas chromatography and a sniffing port (GC-O-HRMS). Multivariate analyses (MVA) were utilized to explore a compound that is likely to be odorous aldehydes or ketones with a reduced time of exploration. A combination of LC-HRMS and MVA resulted in the selection of one candidate substance and its formula was determined to be C13H20O3 on the basis of its accurate mass and natural isotopic pattern. The candidate substance underwent GC-O-HRMS analyses and milk-like smell was detected at around its retention time. Although the detected smell was different from fishy smell, it is expected that the fishy smell is caused by multiple compounds to which the candidate substance belongs. First generation product ion spectra of the candidate substance suggested that it contains a hydroxyl group, a cyclohexene ring, and a ketone moiety.