A new apple polysaccharide for stabilizing goat milk casein dispersion: Rheology, SAXS and intermolecular interaction...

In this study, a newly reported apple polysaccharide (AP) capable of forming gels at ambient temperature or even lower with 0.5 % concentration (w/v) was incorporated in 8.0 % goat milk casein (GMC) dispersion for exploring the potential of AP to stabilize the GMC dispersion at a wide pH range (3.0-7.0). Rheological analysis revealed that the GMC-AP mixture (8.0 % GMC + 0.5 % AP) exhibited remarkable shear-thinning behavior with viscosity exceeding 1000 Pa·s at low shear rate (0.1 s^-1) in pH 3.0-5.0 range. This superior stability stemmed from electrostatic interactions that peaked at pH 3.0 (inducing associative phase separation) and moderately weakened at pH 4.0-5.0 while maintaining system integrity. Multimodal characterization through Zeta-potential, UV-vis/fluorescence spectroscopy, FTIR, and ITC confirmed the pH-responsive binding patterns. SAXS and atomic force microscopy further revealed the formation of intermolecular complexes at pH 3.0-5.0. At higher pH range (6.0-7.0), the viscosity of the system greatly decreased, where the aggregation between AP and GMC as induced by electrostatic interaction still existed but became extremely weaker. Considering AP can stabilize GMC dispersion especially at pH 4.0-5.0, our results may highlight the potential application of AP in GMC-based acidic dairy products.