Interfacial behaviour of succinylated faba bean legumin at low ionic strength

Changes in the tensio-active properties of the main storage protein from fa ba beans (legumin) after succinylation were studied at a low salt concentra tion. Surface tension, surface dilatational properties of monolayers and em ulsifying activity were measured at a ionic strength of I = 0.02. The resul ts were compared with those at a high ionic strength of I = 0.3. Parameters of the Gibbs' adsorption isotherm indicate that the most surface -active derivatives are legumins with a moderate degree of succinylation (3 4% and 65%). The equilibrium surface pressure, Pi(e), inreased from 18.47 ( native legumin) to 20.72 mN/m (65% succinylation). The critical association concentration, CAC, i.e., the subphase concentration at which the plateau of Pi(e) was reached, decreased from 15.9.10(-6) to 7.12.10(-6) g/ml after 34% succinylation. The film forming properties differed from the adsorption behaviour. Only monolayers of the 65% succinylated legumin exhibited visco elastic behaviour. By contrast, the emulsifying activity, EAI, reached the highest values for the 65% and 95% succinylated legumins. Low salt concentrations favour the adsorption of the native legumin and red uce the surface activity of succinylated legumin. Monolayer formation and e specially the ability to form elastic networks seems to be diminished by th e repulsive interaction of like-charged molecules. The emulsifying properti es of the higher succinylated legumins are not influenced by the ionic stre ngth whereas those of the native and low succinylated legumin are distinctl y lower at I = 0.02. This result points to different adsorption and stabili zing processes during emulsion formation.