Lactalbumin, surface viscosities

We report on the use of surface viscosity measurement at the planar oil—water interface to monitor time-dependent structural and compositional changes in films adsorbed from aqueous solutions of individual proteins and their mixtures. Results are presented for the proteins casein, gelatin, oC-lactalbumin and lysozyme at the n-hexadecane— water interface (pH 7, 25 °C). We find that, for a bulk protein concentration of 10 wt%, while the steady-state tension is invariably reached after 5—10 hours, steady-state surface shear viscosity is not reached even after 80—100 hours. Viscosities of films adsorbed from binary protein mixtures are found to be sensitively dependent on the structures of the proteins, their proportions in the bulk aqueous phase, the age of the film, and the order of exposure of the two proteins to the interface. 

C). The logarithm of the apparent surface viscosity is plotted against the time t following exposure of protein solution to fresh interface , -casein (ionic strength 0.005 M) , sodium caseinate (0.005 M) , gelatin (0.005 M) , o<-lactalbumin (0.05 M) A, lysozyme (0.05 M). Lines are drawn to guide the eye. 

Table I lists values of the steady-state tensions for the various individual proteins at the n-hexadecane—water interface. There is no obvious relationship between interfacial tension and apparent surface viscosity. Gelatin and o<-lactalbumin have similar viscosities but very different tensions p-casein and x-casein have similar tensions but very different viscosities. It is interesting to note that, although at short times (. 15 min) the surface activity of sodium caseinate lies intermediate between that for

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