Effect of pH and heat treatment on structure, surface characteristics and emulsifying properties of purified camel ß-casein.

Oil-in-water emulsions (20%/80%, w/w) were stabilised by two types of ß-caseins (1 g/L, w/w) extracted by rennet coagulation from camel and cow's milk, respectively. Both extracts were treated under different ranges of pH (3.0, 6.0 and 9.0) and temperature (25, 65 and 95 °C for 15 min) before emulsification. The emulsifying properties of the proteins were studied by surface and interfacial measurements. Results show that the emulsifying activity (EAI) of camel ß-casein is higher than the bovine protein. Yet, both proteins exhibited heat stability and nonsignificant effect of temperature was reported. Conversely, a significant effect of pH on camel ß-casein was recorded: at pH 6.0, the lowest values of EAI were measured and explained by the formation of micellar protein structure. Under such conditions, camel ß-casein is therefore a novel emulsifying protein with high potential to stabilise oil-in-water interfaces which provides numerous applications for the food chemistry field.

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

Camel α-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 α-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 ζ-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 α-lactalbumin, and Ala-C conferred the highest long-term stability to the emulsions.