Studies on the Interactions Between Mucin and Surfactant Aggregates Containing the Cationic Surfactant Dodecyl Betainate

pH-Dependent Binding Behavior of the α-Lactalbumin/Glycyrrhizic Acid Complex in Relation to Their Foaming Characteristics in Bulk

This work aimed to understand the relationships of the interaction mechanism and foaming characteristics of α-lactalbumin (α-La) and glycyrrhizic acid (GA) after acidic (pH 2.5) and neutral (pH 7.0) treatment. The critical aggregation concentration (CAC) of GA in the presence of α-La was 0.6 mM at pH 7.0, while it was 1.0 mM at pH 2.5. Also, in the presence of a GA concentration of 0-15.00 mM, more GA molecules combined onto the α-La surface at pH 2.5 than at pH 7.0, as evident from the binding isotherms. The turbidity and particle size of α-La/GA were greater in acidic solution than those under neutral conditions. This result could be interpreted by the formation of aggregates under higher GA concentration at pH 2.5. Meanwhile, the viscosity of the complex was higher at pH 2.5 than at pH 7.0 in the presence of 3.00-15.00 mM GA, as analyzed from the rheological properties. The foaming ability (FA) of α-La was significantly enhanced in the presence of 10.00 mM GA. Simultaneously, acidic solution could generate a more stable foaming system with a thicker film layer stabilized by the complex compared with neutral solution. These findings could be beneficial for developing a kind of acidic food-grade foaming agent.

Structural evolution of oleyl betainate aggregates: in situ formation of small unilamellar vesicles

Betaine esters prepared from long-chain alcohols are a class of hydrolyzable cationic surfactants that is interesting both because the compounds can be designed to give harmless products on degradation and that the hydrolysis products can induce potentially useful changes in the properties of systems where such surfactants are present. In this work, the evolution in structure of aggregates formed by oleyl betainate during hydrolysis of the compound has been investigated using (1)H NMR and cryo-transmission electron microscopy (cryo-TEM). With an increasing extent of hydrolysis, and thus an increasing fraction of oleyl alcohol in the aggregates, the aggregate structure changes in a sequence consistent with an increase in the average packing parameter of the surfactant-alcohol mixture, from spherical micelles, via wormlike micelles, to vesicles. An important result from this work is that it demonstrates a means of in situ production of small unilamellar vesicles with a rather narrow size distribution.