De Harlod McGee, "Sobre comida e culinária: a ciência e a sabedoria da cozinha":
The muscles that make up meat are mainly water and the protein fibers that do the work of contraction, which are not dispersable in water. The soluble and dispersable materials in muscle include about 1% by weight of collagen, 5% other cell proteins, 2% amino acids and other savory molecules, 1% sugars and other carbohydates, and 1% minerals, mainly phosphorus and potassium. Bones are around 20% collagen, pig skin around 30%, and cartilaginous veal knuckles up to 40%. Bones and skin are thus much better sources of gelatin and thickening power than meat. However, they carry only a small fraction of the other soluble molecules that provide flavor. (pg 598)
Assim, 7% (5% + 2%) pode ser considerado o limite superior para a extração de proteínas, que obviamente dependerá das especificidades da carne e do processo de cozimento. McGee, em seguida, passa a discutir o processo adequado para extração, começando com água fria gradualmente aquecida:
The cold start and slow heating allow the soluble proteins to escape the solids and coagulate slowly, forming large aggregates that either rise to the surface and are easily skimmed off, or settle onto the sides and bottom. A hot start produces many separate and tiny protein particles that reamin suspended and cloud the stock; and a boil churns particles and fat droplets into a cloudy suspension and emulsion. (pg 599)
Isso também indica que a quantidade de gordura emulsionada dependerá muito do processo de cozimento, além do teor de gordura dos ingredientes originais. (Eu não consegui encontrar muita diferença no processo de extração para diferentes gorduras animais).