EPR Spectroscopy and Imaging of Free Radicals in Food

Electron Paramagnetic Resonance (EPR) is a well‐known spectroscopic and imaging technique that can detect free radicals both in vitro and non‐invasively in vivo, with high sensitivity. In food, free radicals can be generated by several commonly used industrial processes, such as radiosterilization or heat treatment. EPR spectroscopy has been widely used to detect radioinduced free radicals in food, but is limited to the measurement of the global response of a sample. EPR imaging (EPRI) allows the spin density distribution of free radicals to be mapped within objects. We investigated the possibility of acquiring 2D and 3D EPR images of the distribution of free radicals in various foodstuffs with naturally occurring or induced free radicals, including frogs' legs, tea leaves, coffee beans, and sunflower seeds. Our results demonstrated that the free radicals contained in foodstuffs give EPR signals with characteristics compatible with the acquisition of high‐quality images. Small‐size structures (e.g., frog bones, 1.0–1.5 mm width) could be delineated with accuracy. The strongest signals came from irradiated samples, but low‐intensity signals from naturally occurring free radicals could also be imaged. EPRI is likely to be used when additional information is needed about the spatial distribution of unpaired electrons. The method offers the unique ability to monitor the fate of these free radicals in biological samples and in vivo.