The egg white that it is separated mechanically, is contaminated with yolk and loses the ability to form foam. This clear is the pasteurized at 65 ° C for 3 minutes. How can i improve the foam ability?.
The most promising or possibly only way would be to reduce yolk contamination.
Use fresh eggs for breaking as the strength of the yolk membrane decrease with the age of the eggs. Critically examine the machinery and methods used to separate yolk and white. Some (minor) adjustments might be sufficient.
Once you have yolk in the white, I am afraid that there are very little possibilities to obtain a good foaming quality as fat is detrimental for foaming ability.