# The thermal aggregation behavior and functional properties of SPI-catechin complexes under spray-drying conditions

## TL;DR

This study shows that adding catechin to soy protein isolates improves their solubility and functional properties during spray-drying.

## Contribution

The study introduces catechin complexation as a novel method to mitigate thermal aggregation in soy protein isolates during spray-drying.

## Key findings

- Catechin promotes a structural transition in SPI from random coils to α-helical configurations.
- At 1% catechin, SPI solubility improved by 181.09% and emulsifying activity, thermal stability, and foaming stability were enhanced.
- Gel hardness was highest at 0.25% catechin, with disulfide bonds and hydrophobic interactions playing key roles in gel formation.

## Abstract

Commercial soy protein isolates (SPI) often suffer from poor solubility and diminished functional properties due to the harsh conditions of spray-drying. This study demonstrated that catechin complexation effectively modulated SPI thermal aggregation behavior during spray-drying conditions. Structural characterization revealed that incorporating catechin (0.25%-1.75%, w/w) promoted a conformational transition in SPI from predominantly random coil structures to more ordered α-helical configurations. Fluorescence spectroscopy and electrophoresis results suggested hydrophobic interactions dominated between SPI and catechin. Notably, at 1% catechin, thermal aggregation was notably mitigated, transforming insoluble aggregates into soluble ones stabilized by electrostatic forces. At this optimal concentration, SPI solubility improved by 181.09% compared to commercial SPI, while emulsifying activity, thermal stability, and foaming stability were also markedly enhanced. Moreover, at 0.25% catechin, gel hardness reached 1.58 ± 0.02 N, higher than in other groups. Disulfide bonds and hydrophobic interactions were found to be key in forming the gel network.

•Soy protein isolate-catechin (SPI-C) complexes were prepared to inhibit thermal aggregation of SPI during commercial spray-drying processes.•With an optimal catechin concentration, the SPI-C complexes exhibited significantly improved solubility, emulsifying activity, and gel strength.•Structural modifications, interaction mechanisms, and thermal aggregation behavior of the SPI-C complexes were systematically investigated.

Soy protein isolate-catechin (SPI-C) complexes were prepared to inhibit thermal aggregation of SPI during commercial spray-drying processes.

With an optimal catechin concentration, the SPI-C complexes exhibited significantly improved solubility, emulsifying activity, and gel strength.

Structural modifications, interaction mechanisms, and thermal aggregation behavior of the SPI-C complexes were systematically investigated.