Protein-Glutaminase-Mediated Deamidation Enhances the Functional Properties of Walnut Protein Concentrate for Food...

Walnut protein concentrate (WNPC) is dominated by glutelins with compact molecular architecture and low solubility at neutral pH, which severely restrict its functional performance in food systems. This study elucidates the structural mechanisms by which protein-glutaminase (PG)-mediated deamidation remodels WNPC to overcome these intrinsic limitations. Under optimized conditions, PG selectively converted glutamine residues to glutamate, introducing additional negative charges that increased the absolute zeta potential to approximately 30 mV, reduced particle size to below 100 nm, and induced pronounced conformational rearrangements, including a decrease in α-helix content and a concomitant increase in β-sheet structures. These structural changes promoted exposure of sulfhydryl groups and enhanced molecular flexibility, collectively leading to markedly improved solubility, interfacial activity, and emulsifying stability. Model beverage experiments showed that the modified proteins could be used to prepare high-protein walnut beverages with improved physical stability. These results suggest that PG-mediated deamidation may provide a practical approach for improving the functionality of insoluble plant glutelins and expanding their use as food ingredients.