Enzymatic hydrolysis alters the structure and surface properties of Acacia senegal Gum

Abstract

Acacia gum is a naturally occurring, heterogeneous mixture of arabinogalactan-proteins, valued for its surface properties in industrial applications. However, the impact of enzymatic treatments on its structural and functional characteristics remains poorly understood. In this study, the effect of four proteases (papain, subtilisin A, proteinase K, pronase) and three glycosidases (β-galactosidase, β-glucuronidase, α-rhamnosidase) on the structure and surface properties of Acacia senegal (A. senegal) gum were investigated using high-performance size exclusion chromatography with multiangle laser light scattering (HPSEC-MALLS), small angle X-ray scattering (SAXS), and quartz crystal microbalance with dissipation monitoring (QCM-D). The proteolysis effects on A. senegal gum were dependent on the molecular weight (M_w) and protein content of its macromolecular fractions separated by hydrophobic interaction chromatography. The high-M_w arabinogalactan-protein (AGP) fraction, HIC-F2, which constitutes ∼10 % of the total gum with an average M_w of ∼1.6 × 10⁶ g mol⁻¹, was significantly hydrolyzed by all tested proteases, albeit to varying extents. By contrast, the arabinogalactan-peptide (AG-peptide) fraction, HIC-F1, which represents the predominant fraction (∼90 %) with a M_w of ∼3 × 10⁵ g mol⁻¹, exhibited negligible proteolysis. Notably, HIC-F2 hydrolyzed by mixed proteases yielded species with a M_w comparable to HIC-F1. SAXS structural analysis revealed three distinct correlation lengths in both HIC-F2 and HIC-F1, which remained unchanged following proteolysis, likely reflecting multiple length scales of the carbohydrate units. Also, HIC-F2 population was primarily responsible for the surface adsorption of A. senegal gum, whereas HIC-F1 demonstrated minimal interfacial activity. Regardless of their specificity, all proteases significantly reduced the surface load and interfacial viscoelasticity of A. senegal gum, with a strong correlation between the M_w of hydrolyzed AGPs and their adsorption capacity. Conversely, the tested glycosidases did not affect the macromolecular structure of A. senegal gum. This study offers valuable insights into how the structural and functional properties of Acacia gums can be tailored through enzymatic treatments.