Flavonoid with proteins

Arts, M.J.T.J. et al., Masking of antioxidant capacity by the interactions of flavonoids with protein, Food Chem. Toxicol, 39, 787, 2001. 

The flavonoid quercetin suppresses growth somewhat in prairie voles, M. ochrogaster, while tannic acid, a hydrolyzable tannin, has an even stronger effect (Lindroth and Batzli, 1984). Quercetin is toxic, but does not bind with protein and, therefore, does not affect protein digestibility. Tannic acid has some effect on protein digestibility but is also toxic. 

Hatano, T., Yoshida, T., and Hemingway, R.W., Interaction of flavonoids with peptides and proteins and conformations of dimeric flavonoids in solution. In Plant Polyphenols 2. Chemistry, Biology, Pharmacology, Ecology (eds G.G. Gross, R.W. Hemingway, T. Yoshida, and S.J. Branham), Kluwer Academic/Plenum Publisher, New York, 1999, p. 509. 

The interaction of flavonoids with MDR proteins is of interest not only in the field of cancer prevention and therapy but also in the field of flavonoid bioavailability. Indeed, using specific inhibitors of MDR proteins, it was shown that multiresistant protein 2 (MRP2), but not Pgp, is involved in the efflux of quercetin conjugates from human hepatic cells. Similar observations were made with the cell line Caco-2 (a popular model for human intestinal absorption) where MRP2 was found responsible for the efficient efflux of chrysin after its conjugation into a mixture of glucuronide and sulfate. ... 

Flavonoids and other polyphenols can interact with lipids and proteins. The interactions with proteins could be both unspecific or specific, meanwhile the interactions with lipids seems to be rather unspecific, based essentially on physical adsorption. This physical adsorption would mostly depend on the hydrophobic/hydrophilic characteristics of the flavonoid molecule, the number of hydroxyl substituents, and the polymerization degree [Erlejman et al., 2004 Verstraeten et al., 2005, 2003, 2004]. 

Up until now, most of the published work on the SFE of natural products has been concerned primarily with nonpolar substances such as essential oils, lipids, flavor, and fragrance ingredients. However, recent reports have shown that some polar plant constituents (e.g. flavonoid glycosides, proteins, and steroidal glycosides) can be extracted by SFE as effectively as conventional organic solvent extraction. Examples of SFE applications for natural products are well reviewed in several literature sources [19-22]. 

Nonhydrolyzable or condensed tannins are also named proanthocyanidins. These are polymers of flavan-3-ols, with the flavan bonds most commonly between C4 and C8 or C6 (Figure 6-23) (Macheix et al. 1990). Many plants contain tannins that are polymers of (+)-catechin or (-)-epicatechin. These are hydrogenated forms of flavonoids or anthocyanidins. Other monomers occupying places in condensed fruit tannins have trihydroxylation in the B-ring (+)-gallocat-echin and (-)-epigallocatechin. Oligomeric and polymeric procyanidins are formed by addition of more flavan-3-ol units and result in the formation of helical structures. These structures can form bonds with proteins. 

Besides the naturally occurring saccharides and polyols, there are a number of plant-derived highly sweet compounds, which are mostly terpenoids, flavonoids, and proteins [16-18]. Several of these sweet substances are used commercially as sucrose substitutes, as will be described in the next section. In addition, a number of plant substituents are known to mediate the sweet-taste response, either by inducing or inhibiting the perception of sweemess [19]. Thus far, all of the known natural product sweet-tasting substances and sweetness modifiers have been obtained from green plants [16-19]. In the remaining sections of this chapter, plant-derived sweet compounds with commercial use will be described, followed by a section on recent theories on the sweet taste phenomenon, and then individual descriptions of potent sweeteners, sweetness inducers, and sweetness inhibitors from plants will be presented in turn. The literature has been surveyed for this chapter until the end of 1999. 

---