Interactions of gallotannins with proteins, amino acids, phospholipids and sugars

Gallotannins play contrasting roles in food quality. They exhibit strong antioxidative and antibacterial properties, and at the same time show certain antinutritional effects. To explore this possible effect of gallotannins, the interaction mechanism between gallotannins and typical food components was investigated. The molecular structure of gallotannins and their interactions with amino acids (glycine, alanine, proline and leucine) were first studied. It is proved that galloyl groups of gallotannins are hydrophobic sites and that these groups can interact with aliphatic side chains of amino acids through hydrophobic association. Further, the binding of gallotannins (1,2,6-tri-O-galloyl-d-glucose (TGG) and 1,2,3,4,6-penta-O-galloyl-d-glucose (PGG)) to typical proteins, phospholipids and sugars was examined quantitatively. It is indicated that gallotannins bound more to proteins (histone, bovine serum albumin, casein and gelatin) and phospholipids (l-α-lecithin, l-α-cephalin and sphingomyelin) than to sugars, and that PGG had stronger binding affinity to proteins, phospholipids and sugars than did TGG. The gallotannin–protein and gallotannin–phospholipid interactions were the result of cooperative effects of hydrogen bonding and hydrophobic association, and hydrogen bonding was the predominant effect in the interactions between gallotannins and sugars.