Biophenol-Protein Supramolecular Models by Fast Atom Bombardment-Mass Spectrometric Experiments Ka `roly Ve ´key, † Antonio Malorni, ‡ Gabriella Po `csfalvi, ‡ Anna Piperno, § Giovanni Romeo,* ,⊥ and Nicola Uccella* ,§ Central Research Institute for Chemistry of Hungarian Academy of Sciences, Pusztaszerı `u ` t 59-67, H-1025 Budapest, Hungary, Servizio Spettrometria di Massa, CNR, Area di Ricerca di Napoli, Via Castellino 111, Vomero, 80128 Napoli, Italy, CIRASAIA, Universita ` della Calabria, Arcavacata, 7030 Rende (CS), Italy, and Dipartimento Farmaco-chimico, Universita ` , Via SS. Annunziata, 98168 Messina, Italy Biomimetic supramolecular formation between hydroxytyrosol, a biophenol found in olives and virgin olive oil, and caffeine or Asp-Phe, as proteic models, has been achieved by FAB-mass spectrometric experiments. The protonated supermolecules show a consistently higher difference in stability constants, thus indicating a preferential molecular recognition site provided by caffeine, the biomimetic model of proline-rich mucoproteins. The spontaneous aggregation of the complementary supramolecular components suggests correlations with the sensorial response and the bioavailability of food biophenols. Keywords: Biophenols; biomimetic molecular recognition; supermolecules; mass spectrometry INTRODUCTION Molecular microcomponents of Mediterranean foods (Mf) show renewed interest, since they exert many physiological effects in human nutrition and affect the quality and authenticity of traditional products (Ange- rosa et al., 1995). In the vegetable kingdom, biophenols are widely distributed and are present in relative amounts in fruits, leaves, and other vegetable organs. Their molecular activity, as tastant, antioxidative, and chelating functionality, enhances the defensive and protective factors, preserving plant tissues from her- bivorous attack (Baxter et al., 1996). Biophenolic ingredients are naturally found in olives and virgin olive oil and are lost in other refined and seed oils during the various processing stages (Montedoro and Cantarelli, 1969). This non-nutritive portion of the typical Mediterranean diet assumes a fundamental role for the product quality and for its relation to oxidation resistance and the peculiar bitter taste, with further beneficial health effects (Casuscelli et al., 1994). The functional groups of 1 affect sensory and nutritional features of virgin and processed oils (Olias, 1992), being a tastant substrate (St) in their sensorial perception, with a variety of stimuli (bitter, pungent, spicy, sour, astringent) in agreement with its structure and molec- ular complexity (Shallenberger, 1993). Biophenols 1, before eliciting their biological activity, need to reach the proper target in the human body, through a long and complicated journey: beginning from the olive plant, via the mouth, and then down to the cells. Oleuropein, the most important biophenol in olive fruit, and its metabolite demethyloleuropein (Gariboldi et al., 1986) release the 2-(3,4-dihydroxyphenyl)ethanol (hydroxytyrosol, Ht) moiety by enzymatic hydrolysis (Limiroli et al., 1995). In the mouth, Ht may bind to sensorial receptors (Rs) on the tongue and to mucopro- teins (Pm) and other food ingredients (If) in the oral cavity (van der Heijden, 1993). These interactions form supermolecules with globular and proline-rich Pm. The specific supramolecular interaction among Ht, Rs, Pm, and other If may involve absorption and desorption equilibria with formation of charge transfer host/guest aggregates. Molecular biomimetic experiments with olive biophe- nols have been undertaken in order to rationalize the bioactivity of these microingredients and to predict their destination, bioavailability, and sensorial interaction. The biomimetic models to be experimented should have specific features, providing the Ht substrate of appropri- ate sites to be linked with electrostatic forces, hydro- gen bonds, and/or noncovalent interactions, and should have hydrophobic location for biological flexibility and specificity. The interaction of Ht with Rs, Pm, and some If has been studied by the biomimetic model Ht interacting with caffeine (C) or the dipeptide Asp-Phe (Ap), as Rs, Pm, and some If possess proteic structure. Caffeine has been selected for its easy association with monomeric and polymeric biophenols, competing effectively with proteins in the process of supramolecular formation (Baxter et al., 1996). In fact, C is characterized by a * To whom correspondence should be addressed (G. Romeo fax, 39-90-6766562; e-mail, romeog@imeuniv. unime.it; N. Uccella fax, 39-984-492116; e-mail, N.Uccella@unical.it). † Central Research Institute for Chemistry of Hun- garian Academy of Sciences. ‡ CNR. § CIRASAIA. ⊥ Universita ` della Calabria. Chart 1. General Formula of Biophenols 2447 J. Agric. Food Chem. 1997, 45, 2447-2451 S0021-8561(96)00802-3 CCC: $14.00 © 1997 American Chemical Society