Comparative Analysis of Proteins in Two Typical Chinese Thin-Shell Walnuts

This study compared functional properties and molecular characteristics of proteins from two thin-shelled walnut (Juglans regia L.) cultivars predominantly grown in China: Wen 185 and Lvling. Wen 185 walnut protein demonstrated significantly superior performance compared to Lvling across multiple functional parameters, including solubility, emulsifying capacity, foaming capacity, water absorption, and oil absorption. Molecular weight distribution analysis revealed that both proteins contained polypeptides ranging from 10-130 kDa; however, Wen 185 exhibited higher proportions of lower molecular weight fractions (10, 15, 20, and 48 kDa), while Lvling showed greater abundance of higher molecular weight proteins (120 kDa). The higher proportion of low molecular weight proteins in Wen 185 contributed to its enhanced solubility and surface activity. Proteomic analysis identified six proteins exhibiting significant differential expression between the two cultivars. Compared to Lvling, Wen 185 showed upregulation of three proteins enriched in β-sheet secondary structures and downregulation of three proteins with high α-helix content. Furthermore, the upregulated proteins in Wen 185 displayed higher proportions of surface net charges and solvent-accessible surface residues compared to the downregulated proteins. These structural differences correlated with the observed superior functional properties of Wen 185 protein. This study demonstrates that cultivar-dependent variations in protein molecular weight distribution, secondary structure composition, and surface charge characteristics determine the functional properties of walnut proteins. These findings provide molecular insights for selecting walnut cultivars with optimal protein functionality for food applications.