Development of 2D LF-NMR relaxation fingerprinting for pyrazine detection and its application in monitoring photo-induced formation in soybean oil

Pyrazines are key nitrogen-containing heterocyclic aromatics that define the flavor profile of edible oils and serve as indicators of stability and quality. To address the limitations of traditional analytical techniques, such as cumbersome sample pretreatment, excessive organic solvent consumption, and poor feasibility for online monitoring, this study developed and validated a non-destructive detection method based on two-dimensional low-field NMR (2D LF-NMR) relaxation fingerprinting for pyrazine compounds in edible oils. By characterizing signal distributions in the T₁−T₂ relaxation space, this method allows for the rapid, non-invasive identification of target components within complex lipid matrices. Furthermore, using a photo-induced quasi-in-situ 2D LF-NMR dynamic characterization technique, we monitored the dynamic conversion of endogenous precursors to 2-Methylpyrazine in soybean oil under full-spectrum light excitation. This discovery provides direct spectroscopic evidence for the formation of non-thermally induced flavor compounds in oils and outlines a free-radical-mediated pathway for nitrogenous precursor conversion. This study resolves the challenges in the rapid characterizing trace flavor components in oils and provides methodological support for elucidating quality evolution during processing and storage. These findings hold significant theoretical and practical value for advancing green detection systems and development of green detection technologies in the food industry.