Complementation of predigested proteins: a nutritionally and economically advantageous method of by-products...

Proteins were isolated from four animal by-products: bovine skin trimmings, sheep wool, whole bovine blood and inedible chicken carcass. These waste protein sources were digested and solubilized with nonspecific bacterial proteases. Commercial casein and isolated soybean protein were treated similarly. Partially digested proteins were characterized by some physical measurements, lipid content and complete amino acid composition. The protein quality of individual proteins as well as their combinations was tested on the growth of Tetrahymena pyriformis. We found that the nutritional value of high quality proteins (casein, soy) could be significantly enhanced by mixing with low nutritional value protein(s). At the same time, the cost of the protein mixture was substantially reduced. We suggest that complementation of proteins isolated from animal by-products is a nutritionally and economically advantageous method.