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

## TL;DR

Heating soy protein glycinin allows it to bind with hexanal, an off-flavor compound, through structural changes and covalent bonding.

## Contribution

The study identifies a specific lysine site and covalent binding mechanism for hexanal in thermally treated soy glycinin.

## Key findings

- Thermal treatment induces conformational changes in soy 11S glycinin.
- Hexanal binds covalently to the acidic subunit of glycinin via a Schiff base at Lys74.
- The binding alters the protein's secondary structure and affects flavor interactions.

## Abstract

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.

•Conformational changes were detected upon thermal treatment of 11S soy glycinin.•Covalent binding of hexanal to an acidic subunit of 11S was proposed (80 °C pH 7.2).•Mass balance indicated that bond formation likely occurs via a Schiff base pathway.•In silico analysis proposed Lys74 as the most likely site of hexanal binding.

Conformational changes were detected upon thermal treatment of 11S soy glycinin.

Covalent binding of hexanal to an acidic subunit of 11S was proposed (80 °C pH 7.2).

Mass balance indicated that bond formation likely occurs via a Schiff base pathway.

In silico analysis proposed Lys74 as the most likely site of hexanal binding.