Structural modification of soy protein by the lipid peroxidation product malondialdehyde

TLDR

Protein oxidation causes covalent modifications that deteriorate functional properties, and soy protein oxidation is influenced by the type and amount of lipid peroxidation products during storage and processing. The study aimed to examine how the lipid‑peroxidation byproduct malondialdehyde modifies soy protein structure. Malondialdehyde was chosen as a secondary LPO product to probe its oxidative effects on soy protein. Malondialdehyde reacted with ε‑amino and sulfhydryl groups, increasing protein carbonyls while reducing sulfhydryl/disulfide, free amines, and lysine, which led to decreased solubility, surface hydrophobicity, and intrinsic fluorescence and promoted aggregation through non‑disulfide covalent bonds, with β‑conglycinin showing greater sensitivity than glycinin as MDA concentration rose. © 2009 Society of Chemical Industry.

Abstract

Abstract BACKGROUND: Protein oxidation results in covalent modification of structure and deterioration of functional properties of target protein. Oxidation extent of soy protein was affected by the content and type of lipid peroxidation (LPO) products in defatted soybean flours during storage and processing. Malondialdehyde (MDA) was selected as a secondary byproduct of LPO to investigate the effects of oxidative modification of LPO‐derived reactive aldehyde on soy protein structure. RESULTS: MDA reacted with ε‐amino and sulfhydryl groups of soy protein, and resulted in an increase in protein carbonyl groups but a decrease in sulfhydryl/disulfide, free amines and lysine. The decrease in solubility, surface hydrophobicity and intrinsic fluorescence indirectly indicated that MDA induced soy protein aggregation, and results of high‐performance size‐exclusion chromatography directly showed that gradual aggregation of soy protein was induced by increasing concentration of MDA. Results of electrophoresis indicated that MDA caused soy protein aggregation, and non‐disulfide covalent bonds were involved in aggregate formation. CONCLUSION: The results showed that sensitivity of soy protein was related to MDA concentration. Soy protein gradually aggregated with increase of MDA concentration; β‐conglycinin was more sensitive to MDA modification than glycinin. Copyright © 2009 Society of Chemical Industry