Occurrence and Thermal-Activation-Induced Variations of Metal Elements (Ca, Fe, Cu, Zn, Sr, Mo) in Commercially Available Self-Heating Meals.

Self-heating ready-to-eat meals have emerged as a rapidly growing convenience-food category. However, the data for metals alterations during process remain unclear. In this study, we aimed to detect the contents of calcium (Ca), iron (Fe), copper (Cu), zinc (Zn), strontium (Sr) and molybdenum (Mo) in commercially available self-heating meals collected from multiple regions of China. Metal contents were measured by Olympus Vanta VCR handheld XRF metal analyzer. Paired measurements were obtained for each food matrix before and after activation. Geographical distribution of metal occurrence was visualised using ArcGIS. The activation process produced matrix-dependent changes in metal contents. Vegetable components showed the most pronounced decreases, with significant reductions in Ca, Fe and Zn (p < 0.05), consistent with leaching into the cooking medium and thermal degradation of the food matrix. In contrast, meat components exhibited modest but consistent increases in Fe and Zn after activation, which may reflect redistribution among co-heated ingredients, moisture-related concentration effects, or migration from metallic components of the heating pack or packaging; these explanations remain hypotheses that require confirmation in dedicated migration and mass-balance experiments. Rice and noodle matrices showed smaller and less consistent variations. Geographical mapping suggested comparatively higher Fe and Zn levels in samples sourced from eastern coastal provinces, although sampling representativeness should be considered when interpreting this pattern. Overall, the present surveillance data indicate that self-heating activation can alter the metal element profile of ready-to-eat meals in a matrix-specific manner, and support the need for routine monitoring of both nutritionally relevant and potentially packaging-derived metals in this emerging product category.