Chemical inactivation of soybean trypsin inhibitors

Sodium metabisulfite and glutaraldehyde were used alone and in combination to inactive Kunitz trypsin inhibitor (TI) in model systems and TI in lyophilized alkaline soy meal extract. Reaction of glutaraldehyde (0.1 to 3.0%, based on total volume of the reaction mixture) with Kunitz TI (3 mg/ml buffer) at 25 C resulted in 60–75% reduction in activity. Treatment of soy meal extract containing 0.08 mg TI/mg at a concentration of 10 mg sample/ml buffer under similar reaction conditions reduced TI activity only 40%, however. A reaction temperature of 75 C had little additional effect on TI inactivation. On the other hand, sodium metabisulfite (0.05 to 1.0 mM) inactivated >96% Kunitz TI within 1 hr at 75 C and 75–94% of the TI in soy meal extract. The combination of 0.6 mM metabisulfite and 0.5% glutaraldehyde at 75 C inactivated >99% Kunitz TI, and combination of 0.6 mM metabisulfite and up to 3% glutaraldehyde inactivated 88% of TI in soy meal extract vs 91% inactivation with metabisulfite alone. Thus, metabisulfite plus glutaraldehyde inactivated Kunitz TI better than either one alone, while bisulfite alone best inactivated TI in soy meal extract. When the reactions were performed at neutral pH, protein solubility of 80% or better was retained.