Urea-Modified Soy Globulin Proteins (7S and 11S): Effect of Wettability and Secondary Structure on Adhesion

This investigation characterized wettability and adhesive properties of the major soy protein components conglycinin (7S) and glycinin (11S) after urea modification. Modified 7S and 11S soy proteins were evaluated for gluing strength with pine, walnut, and cherry plywood and for wettability using a bubble shape analyzer. The results showed that different adhesives had varying degrees of wettability on the wood specimens. The 7S soy protein modified with urea had better wettability on cherry and walnut. The 11S soy protein modified with 1M urea had better wettability on pine. The 1M urea modification gave 11S soy protein the greatest bonding strength in all the wood specimens. The 3M urea modification gave 7S soy protein stronger adhesion on cherry and walnut than did 11S protein; but with pine, 11S soy protein had greater adhesion strength than 7S soy protein. Measurement of protein secondary structures indicated that the β-sheet played an important role in the adhesion strength of 3M urea-modified soy protein in cherry and walnut, while random coil was the major factor reducing adhesion strength of 7S soy protein modified with 1M urea.