Relaxometric studies for food characterization: the case of balsamic and traditional balsamic vinegars

NMR spectroscopy is a powerful technique for investigating the structure and composition, as well as the physicochemical properties, of foodstuff. NMR-field cycling modality reports about the relaxation times of solvent molecules as a function of the applied magnetic field strength. In the case of aqueous solutions, this methodology is particularly valuable in assessing the interactions of water molecules with paramagnetic and large-size macromolecular systems. 1H NMR field cycling relaxometry has been used to characterize traditional balsamic vinegars and balsamic vinegars of Modena. It has been found that the longitudinal relaxation time (T1) of the water proton resonance is mainly determined by the water molar fraction and the occurrence of dissolved macromolecules and paramagnetic metal ions. Actually, the observed 1H nuclear magnetic resonance dispersion (NMRD) profiles appear markedly affected by the formation of paramagnetic macromolecular adducts. It has been shown that counterfeit specimens can be identified on the basis of the comparison of their T1 and T2 (transverse relaxation time) values with respect to the corresponding values of genuine samples. For the latter ones, a relationship has been found that relates the observed T1 to the age of the vinegar.