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 ([eta]) 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 (gamma) 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 mug/mL and 1 mug/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 (Gamma) was 1.69 +/- 0.17 mumol/m(2) for UHMP, which was lower than the values of SBP (1.88 +/- 0.21 mumol/m(2)) and CP (2.91 +/- 0.57 mumol/m(2)). Correspondingly, UHMP possessed the highest molecular area (A) of 0.99 +/- 0.10 nm(2). 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.