Green tea polyphenols bind to soy proteins and decrease the activity of soybean trypsin inhibitors (STIs) in heated...

Area of Science:

• Food Chemistry
• Protein Biochemistry
• Nutraceuticals

Background:

• Soybean trypsin inhibitors (STIs) reduce protein digestibility.
• Epigallocatechin gallate (EGCG), a major green tea catechin, has potential health benefits.
• Understanding EGCG-soy protein interactions is crucial for food processing.

Purpose of the Study:

• To investigate EGCG-soy protein interactions under various thermal conditions.
• To determine the effect of these interactions on STI inactivation in soymilk.
• To elucidate the structural changes in soy proteins induced by EGCG.

Main Methods:

• Nitroblue tetrazolium (NBT) staining assay.
• Circular dichroism (CD) and fluorescence spectroscopy.
• Particle size distribution and gel electrophoresis.
• Measurement of trypsin and chymotrypsin inhibitory activity (TIA and CIA).

Main Results:

• Soy proteins covalently bind to EGCG, with preferential binding to soluble subunits (α/α', A) after heating.
• EGCG addition, especially post-heating, induced significant changes in soy protein secondary and tertiary structures, increasing random coil formation.
• EGCG binding promoted soy protein aggregation.
• STI activity (TIA and CIA) was significantly reduced when EGCG was added after heating at 100 °C for 10 min.

Conclusions:

• EGCG interacts covalently with soy proteins, altering their structure and promoting aggregation.
• The timing of EGCG addition relative to thermal processing influences its interaction with soy proteins and STI inactivation.
• Optimal conditions for EGCG-mediated STI inactivation in soymilk involve post-heating addition.