Selected ion flow tube – mass spectrometry: detection and real-time monitoring of flavours released by food products

This paper is concerned with the application of our selected ion flow tube mass spectrometric analytical method (SIFT-MS) to the analysis of the complex aromas of some food products. This SIFT/MS chemical ionisation technique, to date mostly applied to breath analysis in medicine and health and safety practice, involves the use of pre-selected H3O+, NO+ and O2+ ions to ‘soft ionise’ the volatile organic compounds (VOCs) that constitute complex mixtures such as food aromas. The kinetics involved are well-defined thus allowing quantification of several trace gases simultaneously in an air sample in real time without the need for pre-calibration. In order to facilitate the interpretation of the spectra obtained for complex mixtures by SIFT/MS we have carried out detailed studies of the reactions of these three ion species with a wide variety of organic compounds including many alcohols, aldehydes, ketone, esters and organosulphur compounds. A large kinetics database has thus been created and general patterns of reactivity are seen which are shown to be invaluable for SIFT/MS analyses. Thus, the SIFT mass spectra for some specific food flavours and for the VOCs emitted by cut onion, crushed garlic and ripe banana are presented and interpreted. Finally, the temporal variations in the concentrations of some of the VOCs emitted by these food products, obtained in real time using SIFT/MS in the selected ion monitoring mode, are also presented, which demonstrate the value of this analytical technique in food research. Copyright © 1999 John Wiley & Sons, Ltd.

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