Single-platform monitoring of methyl linoleate oxidation using Vocus high-resolution chemical ionisation time-of-flight mass spectrometry.

Abstract

Monitoring lipid oxidation is relevant to food quality, safety, nutritional value and shelf life. Furthermore, oxidised lipids and reactive breakdown products can contribute to inflammation, oxidative stress and disease. Oxidation initially produces relatively stable primary hydroperoxides that decompose into oxygenated and volatile secondary products associated with rancid off-flavours and potentially harmful species. Since these compounds span a broad range of volatilities and chemical properties, no single sampling or analytical approach can readily measure them all simultaneously. We evaluated whether NH4+ Vocus high-resolution chemical ionisation time-of-flight mass spectrometry could monitor this progression in methyl linoleate using dynamic solution injection (DSI) and dynamic headspace analysis (DHS). Overall, the temporal patterns observed over 0-168 h agreed with established lipid oxidation chemistry. DSI detected hydroperoxides and other low-volatility oxygenated products, whereas DHS detected volatile secondary products. Monohydroperoxides peaked at 104 h and declined thereafter, intact-chain oxygenated products and cleavage products mostly persisted or accumulated later, while aldehyde-rich headspace signals were strongest at 168 h. Radical-related features were also observed, although these assignments remain tentative. This proof-of-concept study demonstrates that direct-injection mass spectrometry can provide time-resolved monitoring of primary and secondary oxidation products within a single analytical framework, supporting more comprehensive assessment of lipid oxidation chemistry.

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