Formation of complexes between tannic acid with bovine serum albumin, egg ovalbumin and bovine beta-lactoglobulin

Tannic acid (TA) shows strong interactions with proteins and the resulting complexes can be utilized as delivery systems for oral drugs. The complexation of TA with three proteins including bovine serum albumin (BSA), egg ovalbumin (EA) and bovine beta-lactoglobulin (BLG) at pH 7.4 was studied. The tryptophan (Trp) fluorescence of all three proteins was quenched by TA in a static quenching mechanism. BLG showed the highest binding affinity and a smallest binding distance with TA which may suggest that BLG-TA is the most stable complex. The results of circular dichroism, synchronous and three-dimensional fluorescence spectra suggested that the protein structures have been changed at different levels and helix structure was affected more significant than β-strand. Zeta-potential of all three proteins was more negative after binding with TA, which is favorable for the stabilization of protein based nanoparticles. Information derived from this work could be important to potentially use TA-protein complexes as nanoencapsulation systems for oral drug delivery.