Composition of IR64 grain surface as characterized by Static Time-of-Flight Secondary ion Mass Spectrometry

IR64 is a widely disseminated post–Green Revolution indica rice variety across Asia and serves as a benchmark cultivar in rice quality and nutritional studies. This study investigated the compositional differences between brown and milled IR64 rice using an integrated analytical approach combining time-of-flight secondary ion mass spectrometry (TOF-SIMS), gas chromatography–mass spectrometry (GC-MS), and inductively coupled plasma–optical emission spectrometry (ICP-OES). GC-MS analysis showed that rice lipids were dominated by palmitic, oleic, and linoleic acids, with brown rice exhibiting a higher proportion of unsaturated fatty acids (~ 75%) compared with milled rice (~ 56%). ICP-OES revealed substantial mineral losses after milling, including reductions in potassium, phosphorus, magnesium, and zinc. Static TOF-SIMS qualitatively corroborated these trends through the detection of characteristic starch fragments (e.g., m/z 221 and 383), fatty acid carboxylate ions (e.g., m/z 255, 279, 281, and 311), phospholipid-related ions (m/z 184), and elemental ions on the rice grain surface. In this study, although qualitative, TOF-SIMS provided label-free, spatially resolved molecular and elemental information in rice grain with minimal sample preparation. This work demonstrates the application of TOF-SIMS for integrated surface-level compositional profiling of rice grains, complementing conventional bulk analytical techniques.