Methods for the Identification of Tainting Terpenoids and other Compounds from Algae Available to Purchase

Off-flavour compounds produced by algae in freshwater ecosystems were studied for their structure using integrated sensory and spectroscopic methods: mass spectrometry (MS), nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR). Both solvent extraction and thermal desorption were used to isolate and to introduce the compounds into gas chromatography/mass spectrometry (GC/MS) and gas chromatography/Fourier transform infrared (GC/FTIR) systems. Ten ng of a terpenoid compound gave a readable IR spectrum. For ¹H NMR studies the compounds were collected directly into NMR solvent by preparative gas chromatography. About 5 µg of a monoterpenoid compound was needed for a reliable ¹H NMR spectrum. The mass spectral data indicated that the series of odorous substances detected by GC were terpenoid hydrocarbons and a later eluting series of compounds were sesquiterpene alcohols. In addition, one compound with an intense off-odour (aromatic, nitrogen containing compound) and some tainting carboxylic acids (derived from a starch factory) were detected.