Surface Activity of Ultrahigh Methoxylated Pectin of Different Size

Abstract Ultrahigh methoxylated pectin (UHMP), which is of moderate molecular weight (MW, ∼150 kDa) and high methoxylation degree (DM, >90%), is a novel surface-active material. To investigate the effect of MW on the surface activity of UHMP, four small UHMPs (MW=85.90, 67.01, 41.24 and 27.24 kDa) of low MW and DM values above 90% were prepared via enzymatic hydrolysis using commercial polygalacturonase. Low MW UMHPs can reduce the water surface tension to ∼45 mN/m, which corresponds to a larger reduction than that of UHMP (∼55 mN/m). Moreover, their critical micellization concentration was increased to 1∼3 g/L. Surface excess and molecular area data suggested that a suitable reduction in MW enhanced the absorption of UHMP at the O/W interface. However, the analysis of interfacial rheology showed that an interfacial film could not be formed when the MW of UHMP was reduced to 20∼40 kDa. In view of the improved surface activity, the grease-removing power (GRP) of each of the UHMPs was measured and compared with that of citrus pectin (CP). The GRP of CP was 79% at 1.0 g/L, and this value was decreased to ∼20% when the CP concentration exceeded 4.0 g/L due to pectin aggregation. With reduced MWs, the UHMPs presented substantially higher GRP values (80∼90%) than CP, especially at concentrations of 4.0∼10.0 g/L. Increasing the temperature (45°C) can effectively increase the GRP of each pectin. However, small UHMPs still reached larger GRPs (85∼95%) than UHMP (75∼90%) and CP (90% at 2.0 g/L). The experimental results suggested that MW can significantly affect the surface activity of UHMP. UHMPs of various sizes have diverse potential applications, for example, as edible films and surface-active materials in daily chemicals.