Adhesive preparation and modification
SPA was prepared based on previous research (Qi et al., 2012). The aqueous protein extract was prepared by mixing defatted soy flour in water at 6.25% solid content at pH 9.5. NaHSO3 was added to the slurry at 6 g/L on the basis of water volume, and the slurry was stirred for 2 h at room temperature. Then the carbohydrate was removed from soy protein by centrifuging at 12,000 × g. The pH of the supernatant was adjusted to 5.6 with 2 N HCl, centrifuged at 12,000 × g, and the precipitation with 27% solid content was used as the control SPA. The product yield was approximately 45% (wet protein/soy flour), and soy protein was predominantly glycinin. OSA