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Ultrasound-Assisted Covalent Conjugation of Walnut Albumin with Bound Polyphenols: Structural Modulation and
Ziyu Li1,2,3, Lifei Wei1,4, Qiulan Shi5
1College of Food Science and Engineering, Tarim University, Alar 843300, China.
Foods (Basel, Switzerland)
|June 12, 2026
Summary
Covalently modifying walnut albumin (WA) with jujube pomace polyphenols (BPs) improved its functionality. Ultrasound-assisted radical conjugation yielded the best results, enhancing solubility, emulsifying activity, and antioxidant capacity for novel plant-based ingredients.
Area of Science:
- Food Science and Technology
- Protein Chemistry
- Bioconjugation
Background:
- Walnut albumin (WA) has a good amino acid profile but poor solubility and emulsifying properties, limiting its food applications.
- Jujube pomace polyphenols (BPs) are abundant but underutilized by-products with antioxidant potential.
Purpose of the Study:
- To covalently conjugate bound polyphenols (BPs) from jujube pomace with walnut albumin (WA) using different methods.
- To investigate the impact of alkaline and radical conjugation methods, with and without ultrasound, on WA structure and functionality.
- To develop improved plant-based protein ingredients by enhancing WA's properties.
Main Methods:
- Prepared four types of WA-BP conjugates: alkaline-treated (AWA-BPs), ultrasound-assisted alkaline (UAWA-BPs), radical-treated (RWA-BPs), and ultrasound-assisted radical (URWA-BPs).
- Assessed structural changes using techniques like FTIR and fluorescence spectroscopy.
- Evaluated functional properties including solubility, emulsifying activity, foaming capacity, antioxidant activity (DPPH, ABTS+, FRAP), and in vitro digestibility.
- Performed molecular docking to analyze BP-WA interactions.
Main Results:
- Covalent conjugation significantly altered WA's structure, reducing reactive groups and increasing hydrophobicity.
- URWA-BPs showed the highest grafting degree (4.46 mg/g DW) and superior functional properties, including enhanced solubility, emulsifying activity, foaming, and antioxidant capacity (10-17% increase).
- UAWA-BPs demonstrated the lowest in vitro digestibility (54.90 ± 1.60%), indicating improved structural stability.
- Molecular docking confirmed stable interactions between BPs and WA with binding free energies from -5.3 to -7.6 kcal/mol.
Conclusions:
- Ultrasound plays a distinct regulatory role in both alkaline and radical conjugation processes, influencing the final properties of WA-BP conjugates.
- Ultrasound-assisted radical conjugation (URWA-BPs) is an effective method for creating functional plant-based protein ingredients with enhanced properties.
- This study offers valuable insights for developing novel functional ingredients from plant proteins and valorizing food processing by-products like jujube pomace.
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