7988
J. Agric. Food Chem. 2004, 52, 7988−7996
High-Field Nuclear Magnetic Resonance (NMR) Study of Truffles (Tuber aestivum vittadini) LUISA MANNINA,†,§ MICHELA CRISTINZIO,† ANATOLI P. SOBOLEV,*,§ PIETRO RAGNI,§ AND ANNALAURA SEGRE§ Department STAAM, University of Molise, 86100 Campobasso, Italy, and Institute of Chemical Methodologies, CNR, 00016 Monterotondo Stazione, Rome, Italy
A high-field NMR technique was used to analyze aqueous and organic extracts of truffles (Tuber aestivum vittadini) to characterize their chemical composition. Water-soluble metabolites belonging to different classes such as sugars, polyols, amino acids, and organic acids were almost completely assigned by means of one- and two-dimensional experiments (1H-1H COSY, TOCSY, 1H-13C HSQC, 1H-13C HMBC, and 1H-31P HMBC). The 1H spectral assignment of the cell membrane components such as lipids, sterols, and fatty acids extracted in organic solvents was also performed. KEYWORDS: Truffles; Tuber aestivum vittadini; chemical composition; metabolites; NMR
INTRODUCTION
Truffles are the fruiting bodies of the hypogeous fungus that grows in symbiosis with trees such as oaks. Due to their typical organoleptic characteristics, the “black diamonds” have a relevant gastronomic interest and are widely used in European and Chinese cooking. Owing to the commercial value of truffles and the actual interest in the naturally occurring bioactive metabolites of fungi, in past years most research (1, 2) has been focused not only on the formation, the morphology, and the ultrastructure of the truffles (3, 4) but also on the truffle chemical composition, namely, on sterolic and lipidic compositions (5). Different methodologies such as chemical analysis and chromatographic and nuclear magnetic resonance (NMR) techniques are usually used to analyze food. High-resolution NMR is a powerful tool to characterize and to assess the quality and the shelf life of food (6-13). For instance, it has been shown that a high-resolution 13C NMR technique can provide valuable information about the fatty acids’ positional distribution in the glycerol moiety of triglycerides (14, 15): this information can be of crucial importance in the cultivar characterization of olive oils (16), in the analytical characterization of edible oils, and also in the prevention of frauds. On the other hand, the application of high-resolution 1H NMR allowed us to suggest new methodologies for the characterization of olive oils (17, 18), coffee (11), and tomato juice (6). Recently, we have been working on a research project funded by the Italian Ministry of Research aimed to enhance by an ionizing radiation treatment the safety and wholesomeness of fresh products subject to the bacterial contamination (19). Specifically, we have monitored by NMR and ultraviolet (UV) * Corresponding author (telephone +39 0690672385; fax +39 0690672477; e-mail
[email protected]). † University of Molise. § CNR.
techniques the effect of the irradiation treatment on Tuber aestiVum Vittadini extracts. Preliminary results suggested that a low irradiation level (
