Xanthan gum-walnut protein interactions: The influence of pyruvate groups on xanthan gum side chains

Understanding the interaction between xanthan gum (XG) and plant protein is crucial for developing dysphagia diets. XG is a key ingredient in many thickeners designed for this purpose, in which the pyruvate group plays an important role. Despite this, little attention has been paid to how the pyruvate group affects the XG-protein interaction. Here, walnut protein isolate (WP) was blended with XG samples spanning a pyruvate gradient (4.42%, 2.47%, and 0.17% for XG, XG₁, and XG₂, respectively). Decreasing pyruvate markedly reduced thickening capacity, with viscosity dropping from 32.85 Pa·s (XG) to 22.70 Pa·s (XG₁; -30.9%) and 4.96 Pa·s (XG₂; -84.9%). WP-XG mixtures showed 30.87, 18.43, and 4.95 Pa·s for WP-XG, WP-XG₁, and WP-XG₂, respectively, indicating the strongest elasticity reinforcement at intermediate pyruvate substitution. Macroscale tribology showed higher friction after de-pyruvylation (μ = 0.51, 0.64, and 0.65), while colloidal results indicated smaller composites with stable surface charges (Zeta potentials -38.00 to -35.67 mV). Spectroscopic and thermal analyses supported the strongest intermolecular network at partial de-pyruvylation, and molecular simulations further indicated substitution- and subunit-dependent binding, with the highest affinity for 11S-XG (-8.9 kcal·mol^-1). This study would provide a theoretical foundation for the development of XG-regulated plant protein products with desirable performances.