Hydrocolloids with emulsifying capacity. Part 2 – Adsorption properties at the n-hexadecane–Water interface

Abstract

The ability to adsorb at n-hexadecane – water interface of natural hydrocolloids was quantified by dynamic drop tensiometry. Conventional and matured hydrocolloids samples from Acacia senegal, Acacia seyal (AcSey), Sugar Beet Pectin (SBP) and natural untreated Gum Ghatti (GG), were studied in aqueous solutions at pH 4.5. Maturation of A. senegal gum (Acacia (sen) SUPERGUM™ EM2, designated as EM2) increased its ability to lower interfacial tension and the elastic characteristics of the interfacial film. This change in properties can be attributed to the increase in molecular weight and in arabino-galactan-protein (AGP) content. EM2 exhibited the best interfacial properties. Conventional and matured AcSey presented interfacial properties that were similar to conventional A. senegal (GAc), correlating with minimal changes observed in their structural features after maturation. Gum ghatti reacted similarly to EM2 and presented relatively fast kinetic profiles, revealing the good qualities of this gum. The kinetics associated with all the hydrocolloids at pH 4.5 have been described using a mathematical model, from which quantitative parameters as onset time or half-time of interfacial-tension-decrease were determined. Compared to the other hydrocolloids, SBP adsorbs by a different mechanism. However, pectin presented the lowest final interfacial tension and gave the more elastic interfacial film. Acidification of hydrocolloid solutions to pH 3.1 increased both the ability to lower the interfacial tension and the elastic characteristics of interfacial film. The effect of structural modifications on interfacial properties was demonstrated, and clarifies further the already observed emulsification behaviour of the studied hydrocolloid.