Protein-proanthocyanidin interactions during extraction of scots pine needles

Successful protein extractions from Scots pine needles in different buffers (pH 5–9)with PVP-10 and Tween 80 suggest that both hydrogen bonds and hydrophobic interactions are responsible for the formation of insoluble protein-tannin complexes. Gel filtrations did not permit a separation of tannins from solubilized proteins. Contamination of the protein fractions was attributed to proanthocyanidins, both as such and when attached to the proteins. The ability of the soluble protein-proanthocyanidin complexes to adsorb on both Polyclar AT through hydrogen bonding and on Phenyl-Sepharose CL-4B through hydrophobic interactions suggests an amphiphilic capacity on the part of the proanthocyanidin. The factors causing persistent binding between proteins and proanthocyanidins through hydrophobic interactions are discussed. Although the vanillin test confirmed the presence of high molecular weight tannins, they occurred independently of the proteins.