TIME-DEPENDENT SURFACE PRESSURES OF ADSORBED FILMS OF CASEINATE + GELATIN AT THE OIL-WATER INTERFACE

The surface activity of protein at the oil-water interface appears to be an important factor influencing the ease of formation and stability of many food emulsions. Using the drop-volume and pendant-drop methods, the change in tension at the n-hexadecane/water interface was monitored at 25.degree. C during adsorption from aqueous solutions of .alpha.SI- and .beta.-casein, sodium caseinate, gelatin, and mixtures of sodium caseinate + gelatin (protein concentration = 10-3 wt%, pH = 7.2, ionic strength = 0.005 mol dm-3). The 2 experimental methods give identical results. At short times (.ltoreq. 3 min), for caseinate + gelatin, the derived surface pressure is sensitive to protein concentration but not to protein composition. At longer times (.apprx. 15 min), adsorption is predominantly controlled by the caseinate, with the surface pressures of the mixtures lying between those for gelatin and caseinate alone at the same bulk protein concentration.