Protein combining

Protein combining (also protein complementing) is a dietary strategy for protein nutrition by using complementary sources to optimize biological value and increase the protein quality. Originally applied to for animal nutrition, since 1971 it has become a chemical critique of food values of vegetarian dishes.

Protein nutrition is complex because any proteinogenic amino acid may be the limiting factor in metabolism. Mixing can optimize for growth, or minimize cost while maintaining adequate growth. Similarly, human nutrition is subject to Liebig's law of the minimum: The lowest level of one of the essential amino acids will be the limiting factor in metabolism.

Plants are thus rated as protein sources by their limiting amino acids.

The first biochemist to enter the field was Karl Heinrich Ritthausen, a student of Justus von Liebig. Thomas Burr Osborne continued what Ritthausen started and published The Vegetable Proteins in 1909. Thus Yale University was the early center of protein nutrition, where William Cumming Rose was a student. Osborne also worked to determine the essentials, and later led the Biochemistry Department at the University of Chicago.

When Ritthausen died in 1912, Osborne praised his efforts in biochemistry:

Osborne then joined forces with Lafayette Mendel at the Connecticut Agricultural Experiment Station to determine the essential amino acids.

...
Wikipedia