Insight into succinylated modified walnut protein isolate: structural and functional properties, and curcumin release behavior

BACKGROUND: Due to its high glutenin content, walnut protein isolate (WPI) exhibits low solubility, limiting its applications in the food industry. RESULTS: WPI was modified with succinic anhydride (SA), and the potential of the resulting curcumin-loaded emulsions was evaluated. The degree of succinylation of WPI was measured as 89.52 ± 0.66% when 40% SA was used. Succinylation enhanced the surface charge of WPI, reduced its surface hydrophobicity and disulfide bond content, and involved both lysine residues and free sulfhydryl in the acylation reaction. Structural analyses, including Fourier transform infrared spectroscopy, intrinsic fluorescence, and scanning electron microscopy, revealed that SA modification induced significant conformational changes in WPI. Notably, at 20% SA addition, WPI exhibited optimal functional properties, achieving solubility as high as 98.24%. In vitro digestion assays demonstrated that succinylation decreased the release of free fatty acids from emulsions and improved the bioavailability of curcumin to 86.81%. CONCLUSION: This study demonstrated that SA modification is an effective way for enhancing the structural and functional properties of WPI. The SA-modified WPI shows potential as a carrier for improving the solubility and bioavailability of hydrophobic bioactive compounds. Moreover, this work provides new insights into the significance of WPI modification and offers practical guidance for its application in the food industry. © 2026 Society of Chemical Industry.