ALKALI-MODIFIED SOY PROTEINS - EFFECT OF SALTS AND DISULFIDE BOND-CLEAVAGE ON ADHESION AND VISCOSITY

Soy protein isolates were treated with NaCl, Na2SO4, or Na2SO3 (disulf ide bond-cleaving agent) at a pH of 10.0 and 50 degrees C, and the eff ects of these salts on viscosity, adhesive strength on woods, and wate r resistance of the treated isolates were investigated. Viscosity and adhesive strength decreased with increasing concentrations of these sa lts. At a concentration of 0.1 M, these three salts reduced the viscos ity of soy proteins with no significant adverse effects on adhesive st rength and water resistance. Addition of 0.1 M NaCl, Na2SO4, or Na2SO3 reduced adhesive strength insignificantly from 1230 N to 1120, 1060, or 1013 N, respectively. The viscosity of protein isolate modified at pH 10.0 and 50 degrees C in the absence of salts was >30,000 cP. Treat ment with NaCl or Na2SO4 resulted in viscosity reductions to 6000 or 1 050 cP, respectively. The Na2SO3 treatment yielded an isolate with the lowest viscosity of 110 cP and which retained adhesive and water-resi stive properties. The water resistance of modified soy proteins with a nd without 0.1 M Na2SO3 treatment was not significantly different with 3.3 and 6.6% cumulative delaminations occurring after four water soak ing cycles. Treatment with 0.1 M Na2SO3 resulted in an isolate with a 28% decrease in disulfide linkages.