Relaxometric Studies for Food Characterization: The Case of Balsamic and Traditional Balsamic Vinegars SIMONA BARONI,* ,† ROBERTO CONSONNI, ‡ GIANNI FERRANTE, § AND SILVIO AIME | Invento Srl, “Companies Incubator” of the University of Torino, Via Nizza 52, I-10126 Torino, Italy, Istituto per lo Studio delle MACromolecole (ISMAC), NMR Laboratory, CNR, Via Bassini 15, I-20133 Milano, Italy, Stelar Srl, Via Fermi 4, I-27035 Mede (PV), Italy, and Department of Chemistry IFM, University of Torino, Via P. Giuria 7, I-10125 Torino, Italy 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. 1 H 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 (T 1 ) 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 1 H 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 T 1 and T 2 (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 T 1 to the age of the vinegar. KEYWORDS: NMR; fast-field cycling relaxometry; nuclear magnetic resonance dispersion profile; balsamic vinegar INTRODUCTION The last decades have witnessed a growing interest in the search for new tools for food characterization. Any progress in analytical instrumentation is, early or later, exploited to obtain a more advanced description of foodstuff. Often the diffusion of a new methodology is hampered only by the complex sample preparation and the associated costs. Therefore, methods that do not require any (or minimal) sample treatment are highly desired. Over the years, high-resolution NMR spectroscopy has gained an important position among the spectroscopic methods for food characterization thanks to its unique ability to identify (and quantify) all the major low- to medium-molecular weight components by a single spectrum acquisition without the need for any separative procedure. Besides the high-resolution approach, NMR has provided important contributions to the field by the use of its low- resolution (or wide line) modality. Low-resolution methods lack chemical shift information, and the acquired 1 H signal consists of a single absorption containing the information arising from all protons present in the specimen. This approach has been shown to be particularly useful in investigating systems consist- ing of different phases (solid-liquid, water-fat, etc.) (1). However, also in the case of aqueous solutions, the relaxation characteristics of the single-water absorption bring about a wealth of information about the solute molecules that is highly relevant in the characterization of a given specimen. Moreover, the possibility of recording the proton relaxation rate over an extended range of magnetic fields further improves the potential of this approach as it allows us to identify the occurrence of different contributions that can be assigned to various compo- nents of the foodstuff (2, 3). The results presented here aim to show the potential of the field cycling relaxation approach in food analysis. The meth- odology has been applied to the characterization of balsamic vinegars of different aging process, but it can be easily extended to any other foodstuff containing dissolved paramagnetic metal complexes. Over the past few years, traditional balsamic vinegar (TBVM) and balsamic vinegar of Modena (BVM) have received a great deal of attention from different research groups (4-10), mainly aimed at focusing through NMR studies, the characterization * To whom correspondence should be addressed: Invento Srl, Via Nizza 52, 10126 Torino, Italy. E-mail: simona.baroni@invento-lab.com. Fax: +39-11-6706487. † “Companies Incubator” of the University of Torino. ‡ CNR. § Stelar Srl. | University of Torino. 3028 J. Agric. Food Chem. 2009, 57, 3028–3032 10.1021/jf803727d CCC: $40.75  2009 American Chemical Society Published on Web 03/09/2009