Enzymatically-modified soy protein part 2: adhesion behaviour

Adhesive properties of soy protein isolated from soy protein concentrate (SPC) and its modification by proteolytic enzymes (such as papain, trypsin, chymotrypsin and pepsin) and urease were investigated on different types of woods (such as rubberwood, Bhutan pine, teakwood and plywood). Adhesive strength and viscosity of native and enzyme modified soy protein were compared with commercially available adhesives using the same types of woods. Papain and urease modified soy protein isolate (SPI) showed better adhesive strength compared to unmodified SPI adhesive on rubberwood, while chymotrypsin modified SPI showed zero adhesive strength. All enzymatically-modified adhesives showed lower viscosity in comparison to unmodified SPI adhesive. Hydrophobicity of the native and modified SPIs was determined by the sodium dodecyl sulfate (SDS) binding method. Chymotrypsin-modified SPI (CSPI) showed maximum value of hydrophobicity followed by papain and trypsin modified SPI. Urease modified SPI showed only slight increase in hydrophobicity with respect to unmodified SPI. Structural changes after hydrolysis of SPI by different enzymes were investigated by FT-IR spectroscopy. The ratio of the intensity of nu(c=o) of carboxyl and amide I or ratio of nu(c=o) of carboxyl and amide 11 showed maximum value in case of pepsin modified SPI followed by chymotrypsin modified SPI. Papain, trypsin and urease modified SPIs showed only slight increase in the ratio of carboxyl/amide I or amide II.