Chemical modification strategies for synthesis of protein-based hydrogel

A soy protein-based hydrogel capable of imbibing a large amount of water was synthesized by first modifying the lysyl residues of soy protein isolate (SPI) with ethylenediaminetetraacetic dianhydride (EDTAD) followed by cross-linking with glutaraldehyde. Modification of SPI with EDTAD at pH 9 resulted in polymerization involving intramolecular cross-linking of soy 11S and 7S globulin, which decreased the number of carboxyl moieties introduced per lysyl residue and impaired the swellability of the hydrogel. Pretreatment of SPI involving heating for 30 min at 65 degrees C and pH 12.0 followed by modification with EDTAD at 25 degrees C/pH 12 did not result in polymerization and, under these conditions, about 3.3 carboxyl moieties/lysyl residue were incorporated into the protein. The hydrogel prepared under these conditions was able to absorb more than 105 g of water/g of dry gel. The structural changes in SPI caused by the modification and its relevance to swelling properties of the gel are discussed.