Surface and interfacial activities and emulsion characteristics of some food hydrocolloids

Abstract

Surface and interfacial tensions of numerous hydrocolloid solutions are presented. The surface activity of different types of Methocels, methylcellulose (Methocel A) and hydroxypropyl methylcelluloses (Methocels E, F and K), having similar molecular weights (and hence similar viscosities) increases slightly in the following order: Methocel A < Methocel K < Methocel F < Methocel E. In terms of interfacial activity, the methylcellulose (Methocel A) is less active than the hydroxypropyl methylcelluloses (Methocels E, F and K). Accordingly, oil-in-water (O/W) emulsions prepared using Methocels E, F and K had similar but smaller oil droplets and similar centrifugal stability compared to that prepared using Methocel A due to the presence of hydroxypropyl groups. In a given type, e.g. Methocel E, the surface and interfacial activities seem to be practically unaffected by the molecular weight. The same is true in the case of propylene glycol alginate (PGA). Emulsion results showed that, at a similar interfacial activity, as the molecular weight (and hence the viscosity) increased the emulsion became slightly more stable. Although PGAs are interfacially less active than the Methocels, they yielded more stable O/W emulsions—indicating the importance of functional groups in providing stability to the O/W emulsions. The interfacial activity observed in the case of some of the non-surface active hydrocolloids, such as guar gum and locust-bean gum, was ascribed to the presence of residual surface-active impurities in them.