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 yet been exploited. Paramagnetic metal ions, either naturally present or added to foodstuff, provide an addnl. 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. The present of paramagnetic metal ions such as iron(II) and iron(III) induces isotropic shifts and nuclear relaxation that can be exploited to obtain information, e.g., about food aging. Paramagnetic relaxation effects are also measured on the water pool of foodstuff, and this should be taken as a caveat for the current interpretation of water proton relaxation changes only in terms of changes in hydration and cellular structure of tissues.