EPR Spectroscopy and Imaging of Free Radicals in Food

Philippe P. Levêque, Quentin Godechal, and Bernard Gallez*
Biomedical Magnetic Resonance Unit, Université Catholique de Louvain, REMA 73-40, Avenue Mounier 73, B-1200,
Brussels, Belgium

(Received 9 January 2008 and in revised form 22 February 2008)

Abstract.
 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.