Paramagnetic Challenges in NMR Measurements of Foods

NMR spectroscopy is more and more used in the evaluation of food quality, although all its potentialities have not been yet exploited. Paramagnetic metal ions, either naturally present or added to foodstuff, provide an additional source of information that can help to characterize the food. The presence of “paramagnetic” signals in spectra of complicated systems is extremely helpful for their interpretation and provides information otherwise not obtainable. In complex mixtures, NMR spectra are diagnostic, for example, for the oxidation and spin states of iron porphyrins in myoglobin and hemoglobin, yielding information about the metal ion coordination sphere. In turn, the latter determines the extent to which paramagnetism affects the relaxation rates of those water molecules that are able to bind protein sites in proximity of the heme pocket; the relaxation enhancement is then transmitted to the bulk water molecule by chemical exchange. Some possible exploitations of the paramagnetic effect in food science will be suggested, hoping that their use, already successful in structural biology, will soon bring to meaningful results in the food area.