490 N. Terrier et al.
9B.4.3 Flavonoid Interactions with Other Macromolecules
9B.4.3.1 Interactions with Proteins
Interactions between tannins and proteins have been extensively studied (Hager-
man 1989; Haslam and Lilley 1988; Haslam et al. 1992), owing to their role in haze
formation, astringency perception, and nutritional and anti-nutritional effects result-
ing from inhibition of various enzymes and reduction of dietary protein digestion.
Other effects include reduced adsorption ofβ-casein at the air-liquid interface in the
presence of epigallocatechingallate with potential consequences on foam properties
(Sausse et al. 2003).
Actors
Flavonoid protein complexation shows littlespecificity. However, lower molecular
weight flavonoids (i.e. flavonols, non galloylated flavanol monomers) display mod-
erate affinity for proteins and do not form aggregates. Similarly, although all pro-
teins interact with tannins, proline rich structures such as encountered in proteins
most commonly used as fining agents (e.g. gelatin, casein) or in salivary proline
rich proteins (PRP) involved in astringency perception, are particularly prone to
interact with tannins. Binding of flavonols and flavones to some proteins such as
serumalbumine which is involved in their transport in plasma is well documented
(Boulton et al. 1998; Dufour and Dangles 2005). Flavonols have also been shown
to adsorb on polyvinylpolypyrrolidone (PVPP) (Laborde et al. 2006) but they have
not been reported to interact with wine proteins.
Interaction Mechanisms
Interactions between flavonoids and proteins rely upon both Van der Waals-London
interactions and hydrogen bonding (Oh et al. 1980; Luck et al. 1994; Murray
et al. 1994; Charlton et al. 1996). A study performed by using NMR indicated
stacking of the phenolic rings with the proline residues in proline sequences and
stabilisation of the complexes through hydrogen bonding between the H acceptor
site of the adjacent peptide bond and the hydrogen atom of the phenolic hydroxyl
(Murray et al. 1994). More recently, an isothermal titration calorimetry (ITC)
experiment showed that the interaction of flavanols with poly-L-proline involves
both entropic (associated to hydrophobic effect and conformational changes) and
enthalpic (attributed to hydrogen bonding) phenomena (Poncet-Legrand et al. 2007).
The latter is prevalent in the case of flavanol monomers and the former in that of
polymers. Interaction does not necessarily lead to precipitation. Flavonoids can form
soluble complexes with peptides and proteins, as shown by NMR
(Baxter et al. 1997b; Charlton et al. 2002b; Hemingway et al. 1999), mass spec-
trometry (Sarni-Manchado and Cheynier 2002) or fluorimetry (Dufour and Dan-
gles 2005). Aggregation of flavanols with casein (Jobstl et al. 2006), poly-l-proline