Effect of temperature on interactions between soy 11S glycinin and hexanal - An off-flavour compound

Thermal processing of soy proteins is known to promote interactions with lipid-derived aldehydes, yet the molecular basis and site-specificity of these reactions remain poorly defined. It is hypothesised that heat-induced structural rearrangement of soy 11S glycinin exposes discrete reactive sites within the protein, enabling preferential and potentially covalent binding of aldehyde flavour compounds. To test this, a simulated thermal treatment was performed for 20,000 ps at 353.15 K (80 °C). Following this thermal treatment and subsequent hexanal docking, a new preferential binding location nearing a lysine residue was identified, positioned within the hydrophobic core of the acidic subunit of the individual 11S chain. Traditional benchtop experiments, UV-vis spectroscopy and MALDI-TOF/MS, complemented these findings following analysis of 11S glycinin-hexanal mixtures treated at 80 °C for 60 min. MALDI-TOF/MS revealed a mass increase of approximately 84 Da, consistent with Schiff base formation between hexanal and the acidic subunit, indicating a condensation reaction rather than purely non-covalent association. Such interactions caused significant, quantifiable changes in the secondary structure of the protein determined by FTIR and CD analyses. This mechanistic insight advances understanding of flavour-protein interactions in thermally processed soy systems, aiding in the prediction of flavour retention, off-flavour formation, and protein functionality in food matrices.