Effect of interaction between tea polyphenols with soymilk protein on inactivation of soybean trypsin inhibitor

Soymilk is a popular health beverage worldwide, but its nutritional value is limited by soybean trypsin inhibitors (STIs). The interaction of tea polyphenols (TPs) with soymilk protein in the complex system was investigated in this work. TPs interacted with soymilk protein via static quenching process and hydrophobic interaction, with binding constant (K-a) of 5.22 x 10(3) L mol(-1) at 298 K. Synchronous fluorescence suggested that the binding site of TPs to soymilk protein was mainly at Trp residues compared with Tyr residues. FTIR analysis revealed that hydrogen bonds were also observed in TPs-soymilk system. CD spectroscopy suggested that the protein conformation became more stable with addition of TPs by reducing beta-sheet and random coil, and increasing a-helix and beta-turn. The trypsin and chymotrypsin inhibitory activities (TIA and CIA) were reduced at 0.6 mg/g TPs in cooked soymilk from 788.3 +/- 10.4 U/mL and 918.7 +/- 18.0 U/mL to 388.3 +/- 35.5 U/mL and 633.3 +/- 52.8 U/mL, respectively.

Automated summary

Tea polyphenols interact with soy milk protein through static quenching and hydrophobic interactions, with a main binding site at Trp residues. This interaction stabilizes the protein conformation and reduces trypsin and chymotrypsin inhibitory activities in cooked soy milk when tea polyphenols are added.