Camel α-lactalbumin at the oil-water interface: Effect of protein concentration and pH change on surface characteristics and emulsifying properties

Camel alpha-lactalbumin (Ala-C), the main whey protein of camel milk, was purified by membrane filtration. Surface hydrophobicity as well as interfacial tension were examined at different levels of pH (3.0, 6.0, 9.0) and protein concentration (0.1 %, 0.2 %, 0.4 % w/w), and compared to bovine alpha-lactalbumin (Ala-B). The emulsifying properties (EAI and ESI) of oil-in-water emulsions (20 %/80 %) were investigated for both proteins. The stability of the processed emulsions was characterised by zeta-potential, particle size and viscosity measurements. The main findings indicate that Ala-C exhibited greater surface hydrophobicity and undergone changes in conformational structure when pH decreased from 9.0-3.0. These changes were enhanced by increasing protein concentration from 0.1 % to 0.4 % (w/w). However, high concentrations showed low emulsifying activity, especially at pH 6.0 where interfacial tension was lower. In comparison with Ala-B, maximum EAI was close, despite the lower surface hydrophobicity of Ala-C under similar conditions. Overall, emulsions were more viscous at pH 3.0 due to the greater surface coverage than at 9.0 and 6.0. Under the conditions of this study, a protein concentration of 0.2 % resulted in the finest oil droplets and highest viscosity for both types of alpha-lactalbumin, and Ala-C conferred the highest long-term stability to the emulsions.