When protein molecules are adsorbed onto the interface, they may change tertiary structure to suit the new environment, such as specific orientation and film formation to obey the law of thermodynamics. Specifically this results in the reduction of surface energy, which makes the achieved thermodynamic state more stable. Compounded by the fact that proteins are slow-diffusing molecules, the kinetics of reducing interfacial tension by the addition of protein is not a fast one. According to Ghosh and Bull (8), the surface tension of 0.06% egg albumin solution (pH 4.9, 30°C) dropped from 62 to 48 dyn/cm within a period of 55 min. Graham and Phillips (9) also reported that the process of reduction of surface tension due to the addition of relatively low protein concentrations can take between 10 and 60 min. Kitabatake and Doi (6) reported that the reduction of surface tension due to added protein follows first-order kinetics. They also found that the formability of the protein solution correlated better with the first-order rate constant of the surface tension reduction process than with the equilibrium surface tension of the solution. In other words, formability involves the capacity to entrap air on whipping, which is promoted by proteins that will cause a fast reduction in the surface tension of water.

There are structural similarities between foams and emulsions; surface tension and interfacial tension are important physical parameters to be dealt with in food processing for the former and the latter, respectively.

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