Effect of Peroxyl Radical-Induced Oxidation on Functional and Structural Characteristics of Walnut Protein Isolates Revealed by High-Resolution Mass Spectrometry

Abstract

The present study aims to investigate the structural and functional properties of oxidated walnut protein isolates (WPI) by 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH). The oxidation degree, changes in structural characteristics, processing properties, and protein modifications of WPI were measured. The results showed that oxidation significantly induced structural changes, mainly reflected by the increasing carbonyl content, and decreasing sulfhydryl and free amino groups. Moreover, the secondary structure of WPI was altered in response to oxidation, and large aggregates formed through disulfide cross-linking and hydrophobic interactions. Almost all the property indicators were significantly decreased by oxidation except the foaming property and water/oil holding capacity. Mass spectrometry analysis showed that 16 different modifications occurred in amino acid side chains, and most of the protein groups with higher numbers of modifications were found to be associated with allergies, which was further confirmed by the reduction in antigenicity of the major allergen (Jug r 1) in WPI. Meanwhile, we used oxidation-related proteins for gene ontology (GO) enrichment analyses, and the results indicated that 115, 204 and 59 GO terms were enriched in terms of biological process, molecular function, and cellular component, respectively. In conclusion, oxidation altered the groups and conformation of WPI, which in turn caused modification in the functional properties correspondingly. These findings might provide a reference for processing and storage of walnut protein foods.

Effect of different sweeteners on the quality, fatty acid and volatile flavor compounds of braised pork

“…Most protein oxidation happens on the side chain of amino acid residues. Oxidation can result in structural modifications to proteins, such as aromatic hydroxylation, sulfhydryl oxidation, and carbonyl formation ( 47 ). Frequently, alterations in the muscle fiber structure of meat products are the result of heat treatment.…”

Walnut Protein: A Rising Source of High-Quality Protein and Its Updated Comprehensive Review

“…The results showed that oxidation treatment could significantly increase the carbonyl group, reduce the sulfhydryl group, change the secondary structure, and increase the foaming and water/oil holding capacity of protein. 63 Chemical phosphorylation modification can improve the functional properties of proteins by changing their internal structures and surface properties. Generally, the mechanism of phosphorylation modification is based on the introduction of phosphate groups into the side chains of amino acid residues to increase the electronegativity of proteins and then affects their functional properties.…”

“…Zhang et al studied the effect of water-soluble radical initiator 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) to oxidize WP on the structural and functional properties of the protein. The results showed that oxidation treatment could significantly increase the carbonyl group, reduce the sulfhydryl group, change the secondary structure, and increase the foaming and water/oil holding capacity of protein . Chemical phosphorylation modification can improve the functional properties of proteins by changing their internal structures and surface properties.…”

Protein oxidation‐induced changes in the physicochemical properties and quality of plant food

“…However, moderate oxidative modification could promote the partial unfolding of rice bran protein and improve its water retention and emulsification (Wu et al ., 2020a). Besides, the foaming and water‐holding capacity of walnut protein were also improved to varying degrees after oxidation (Zhang et al ., 2022c). Metal‐catalysed oxidation of pea protein increased the aggregation stability of the droplets during emulsification, and the structural interface of pea protein milk was more uniform (Hinderink et al ., 2020).…”