Effect of proanthocyanidins on protein composition, conformational structure, IgE binding capacities and functional properties in soybean protein

This study was performed to determine the crosslinking formed by proanthocyanidins (PC) with respect to IgE binding capacities, functionality, structure and composition of soybean protein (SPI) following the alkali treatment at 60–100 °C. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS–PAGE) showed the formation of >180 kDa polymers, resulting from the formation of SPI-PC conjugates and protein cross-links. Structural analyses demonstrated that SPI-PC conjugates exhibited structural changes to unfold proteins and increase molecular flexibility. Liquid chromatography coupled to tandem mass spectrometry (LC/MS-MS) showed a decrease in unique protein and peptide numbers as well as major allergen and dominant epitopes abundance. When SPI was treated with PC under the alkali treatment at 80 °C, it exhibited a maximum reduction (68.8 %) in the immunoglobulin E (IgE) binding capacity and a maximum increase in DPPH radical scavenging activities (6.11-fold), ABTS + radical scavenging activities (4.80-fold), foaming stability (6.1 %) and emulsifying activity (27.3 %), compared to the control SPI. Overall, this study demonstrates that alkali treatment at 60–100 °C to form SPI-PC conjugates has potential applications for producing hypoallergenic soybean products with the desired functionality, most especially from alkali treatment at 80 °C. Moreover, the addition of PC pronouncedly alleviates the undesirable functional properties in heated SPI.