Colloidal characteristics, emulsifying activities, and interfacial properties of α-lactalbumin-chitosan electrostatic complexes: effects of mass ratio and pH
The essential hydrophobic carrier properties of α-lactalbumin (α-LA): chitosan (CHI, Mw 100 kDa, degree of deacetylation 75-85%) including mass ratio and pH on the characteristics, emulsifying activities, and interfacial properties of α-LA-CHI complexes were investigated. The interaction between α-LA and CHI was dominated by electrostatic interactions. Soluble α-LA-CHI complex can be formed at both pH 6.0, and 6.5 at mass ratios of 1:1, 2:1, and 5:1, as shown by the optical appearance. UV-vis spectra demonstrated that the interaction between α-LA and CHI is highly CHI concentration, and pH-dependent. AFM graphs showed that α-LA-CHI complexes are spherically shaped and homogeneously dispersed in solution, with diameters around 100-250 nm, in accordance with DLS results, though some aggregates were observed for the 1:1 α-LA-CHI complex. The emulsifying activity of α-LA was enhanced by complexation with CHI. Both emulsifying activity index (EAI) and emulsifying stability index (ESI) of α-LA-CHI complexes were associated with mass ratio and pH values. Interfacial tension of α-LA-CHI complex was negatively linearly correlated with EAI. The lower the interfacial tension of α-LA-CHI complex on oil-water interface, the higher the EAI. The results obtained from this study were complementary and provided insights into the interaction between α-LA and CHI, and suggested that α-LA-CHI complexes can be utilized as effective food ingredients for stabilizing, protecting, and delivering hydrophobic nutraceuticals.