Effect of oxidation on the emulsifying properties of soy protein isolate

Soy protein isolate (SPI) was oxidized by peroxyl radicals derived from 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) and the structural and emulsifying properties of oxidized SPI were evaluated. Increasing extent of oxidation resulted in gradual carbonyl group generation, free sulfhydryl group degradation and dityrosine formation. Moderate oxidization could generate soluble protein aggregates with more flexible structure while over-oxidization would induce the formation of insoluble aggregates. Compared with the control, emulsions stabilized by moderately oxidized SPI had smaller droplet size and better thermal stability. Results from creaming index and microstructure measurement after 15 days indicated that emulsions stabilized by SPI of over-oxidation underwent severe droplet aggregation during storage while moderate oxidation had a positive effect on the emulsion stability.

► Structural and emulsifying properties of AAPH-modified SPI were evaluated. ► Oxidation induced structural changes in SPI. ► Moderate oxidation had positive effects on the emulsifying properties of SPI. ► Over-oxidation deteriorated the emulsifying properties of SPI.