Soy Flour Adhesive Strength Compared with That of Purified Soy Proteins*

Abstract

Abstract Although proteins are naturally good adhesives, often the most economical source has a significant carbohydrate component. Our prior studies have shown that commercial soy protein isolates (CSPI) give very good dry and wet bond strength for wood bonding, but the strengths are much lower for soy flour, especially under wet conditions. One large difference between these soy products is the percentages of carbohydrates, which generally provide poor bond strength under wet conditions. A variety of commercial isolates, concentrates, and flours were examined for their adhesive properties using a small-scale bond test that emphasizes cohesive bond strength. In studying how much the carbohydrates weaken the bond strength, we learned that the carbohydrate interference is only part of the difference between commercial soy flour and purified soy proteins (isolate and concentrate). An even larger factor is the denaturation of the isolate in the CSPI. Thus, it is important to realize that the CSPI performance may not be a good predictor of properties that can be expected from soy flours.