Measurement of lipid oxidation-derived volatiles in fresh tomatoes

Abstract

Abstract A rapid, low-shear, reproducible maceration device was developed for tomato fruit and coupled to an Atmospheric Pressure Chemical Ionisation-Mass Spectrometer (API-MS) so that real time, simultaneous measurement of nine key volatile compounds released upon disruption of the tomato tissue was achieved. The minimum detection level of the volatiles was around the odour threshold concentrations of the compounds and variation between release from macerated tomatoes was between 10 and 25%. Based on their temporal differences in release, the compounds were classified into two groups: the preformed compounds already present in the ripe fruit (isobutylthiazole, 6-methyl-5-hepten-2-one, methylbutanal, methylbutanol, ethanol and acetaldehyde) and the enzyme generated compounds formed only upon maceration (hexanal, hexenal and hexenol). The addition of exogenous linoleic and linolenic acids (2 mg/g FW) to tomatoes prior to maceration influenced the amount of C6 aldehydes produced. Hexanal was increased 12-fold in the presence of linoleic acid, while hexenal was increased 14-fold in the presence of linolenic acid. Addition of both fatty acids gave intermediate behaviour. Addition of enzymes from the lipid oxidation pathway (lipase, phospholipase, lipoxygenase and alcohol dehydrogenase) at various concentrations, in buffer or emulsion and with or without fatty acids caused no significant changes in the release profile of tomatoes. Results highlighted the inhibitory effect of Tween 20 used as surfactant in emulsions. Alternative surfactants (lecithin and glyceryl monostearate) were tested and did not influence volatile generation. The paper demonstrates that the maceration device coupled to the API-MS can be used for rapid screening of tomato fruit as well as for studying the factors that influence the lipoxygenase pathway.