Interfacial properties of ultrahigh methoxylated pectin

The interfacial properties of ultrahigh methoxylated pectin (UHMP) prepared via esterification of citrus pectin (CP) were investigated. The intrinsic viscosity ([η]) of pectin was significantly decreased from 1211.5 mL/g to 294.9 mL/g as the degree of methylation (DM) increased from 63.18 ± 0.08% to 91.52 ± 0.11%. Surface tension (γ) analysis indicated that UHMP had a critical micelle concentration (CMC) of 0.8 g/L, which was slightly smaller than that of sugar beet pectin (SBP) (1.0 g/L). The morphology of the UHMP aggregation presented a network structure and irregular clusters at 10 μg/mL and 1 μg/mL based on atomic force microscopy (AFM). Transmission electron microscopy (TEM) observations further confirmed the self-aggregation behaviours and rod-like micelles of UHMP. The surface excess (Γ) was 1.69 ± 0.17 μmol/m² for UHMP, which was lower than the values of SBP (1.88 ± 0.21 μmol/m²) and CP (2.91 ± 0.57 μmol/m²). Correspondingly, UHMP possessed the highest molecular area (A) of 0.99 ± 0.10 nm². Thus, UHMP was proposed to be more flexible and extendable at the interface. The interfacial shear rheology study suggested that UHMP was able to form an elastic-dominant interfacial film to stabilize the oil/water interface.