Dual H–O isotope tracing of oxidized triacylglycerols in triolein (180°C): mechanisms and control-oriented monitoring indicators

Oxidized triacylglycerols (OxTGs) formed during frying degrade oil quality and raise safety concerns. To resolve oxygen provenance under frying-like conditions, a dual hydrogen–oxygen stable-isotope tracing design (D 2 O, H 2 18 O, 18 O 2 ) was applied to triolein heated at 180 °C for 0–4 h under 3 atm: natural air (NA) + H 2 O, synthetic air (SA)– 16 O 2  + H 2 18 O, and SA– 18 O 2  + D 2 O. Diagnostic fragment ions revealed five triacylglycerols and eight OxTGs dominated by hydroperoxide (–OOH) and hydroxyl (–OH) functionalities, while isotopologue ratios (M+1–M+4)/M quantified label incorporation. Pronounced enrichment occurred only under SA– 18 O 2  + D 2 O, particularly for hydroxylated OxTGs; ratios remained comparatively stable in NA + H 2 O and SA– 16 O 2  + H 2 18 O, consistent with water acting primarily as a kinetic modulator of hydroperoxide turnover and interfacial processes rather than as a direct oxygen donor to OxTGs.The labeling pattern demonstrates that oxygen incorporated into OxTGs derives primarily from molecular oxygen (O 2 ). Mechanistically grounded process controls that limit oxygen availability—such as vacuum or otherwise deaerated frying—are therefore expected to suppress OxTG formation. For decision-ready surveillance and oil-turnover management, an integrated indicator panel is recommended, combining total polar compounds (TPC), sentinel glycerol-core aldehydes (e.g., 9-oxo/10-oxo species), and representative –OOH/–OH OxTGs. Collectively, these findings clarify OxTG formation pathways and provide a practicable basis for risk-informed quality and safety control of frying oils.