Free vs Total Amino Acids: Which Assay Should You Order?

In our work, clients often raise the question: what difference does it make which amino acids to test — free or total? I should like to explain to our clients, very simply, what the difference actually is.

A free amino acid is one that is not part of a protein chain. It has either been added from a substance (i.e. synthetic) or was already present in free form in another raw material.

Bound amino acids are those found within a protein chain (in a peptide), in a complex helix. In other words, they are the amino acids that make up the protein.

Total amino acids are the sum of both forms.

So what should you order?

If you wish to check the content of synthetic amino acids in a product (those added from a substance), you should order an analysis of free amino acids.

If, however, you wish to know the total quantity of an amino acid — lysine, for example — then you should order an analysis of the total lysine content.

Why is it so important to clarify this point? Premixes with a lower inclusion rate are often composed not only of synthetic amino acids but also of haemoglobin and other protein-containing raw materials; and if this is not clarified, then, as a rule, only the synthetic amino acids are determined for the premix. Sometimes a complete feed needs to be tested solely for its content of synthetic amino acids (from a substance).

And the analysis of the free and bound forms differs considerably.

The simplest way to get your bearings is also to discuss the matter with a laboratory representative. We shall always be glad to advise you.

Anastasia Shuparska, Head of the Halomlab Laboratory

21 January 2021