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.
Highlights
Walnut (Juglans regia L.) is one of the common tree nuts widely grown worldwide
walnut protein isolates (WPI) was extracted by the alkali dissolution-acid precipitation method according to Qin et al [9] with slight modifications
The results of this study indicated that numerous modifications occurred in oxidized WPI, whereas carbamidomethyl and oxidation was the most significant indicator
Summary
Walnut (Juglans regia L.) is one of the common tree nuts widely grown worldwide. The planted area and production of walnuts in China ranks first in the world [1]. Walnut kernels are widely consumed in China (409,608 metric tons in 2019) and even worldwide (914,383 metric tons in 2019) for their health promotion and delicious taste [4]. As one of the main by-products of the oil industry, walnut protein has great potential of high value utilization. There have been gradually increasing studies on walnut protein due to its large amount of consumption, such as classification and characterization [5], characteristics analysis and functional properties modification [3,6,7,8,9]
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