Intermolecular interactions in phytochemical model systems studied by NMR diffusion measurements

Novel functional foods, such as tomato juice with soy, represent a new strategy to increase consumption of health promoting ingredients and phytochemicals. Interactions between soy protein, isoflavones, and tomato carotenoids could impact the bioaccessibility and bioavailability of individual phytochemicals. The primary objective of this study was to assess possible interactions between daidzein and daidzin, soy protein and carotenoids using proton one-dimensional and two-dimensional pulsed field gradient nuclear magnetic resonance spectroscopy experiments.The NMR results on phytochemical model systems indicate that the affinity between the daidzin and the soy protein isolate are higher as compared to the daidzein dissolved in the same model system. Two contributions to the interactions between the phytoestrogens and the protein were detected. The first involved intermolecular hydrogen bonding from hydroxyl groups. The second resulted in the shifting of the NMR signal related to the proton on the pyranone ring of isoflavones, suggesting a hydrophobic interaction. Diffusion NMR measurements showed that the addition of carotenoids to the soy isoflavones/protein mixture did not affect the diffusion coefficient of the polyphenols.