Tryptophan is relatively stable but to avoid any degradation, it is best added to the medium after membrane filtration rather than before heat sterilization. This ensures its full activity for IAA determination.

Abdelhak Maghchiche If I sterilize the medium with tryptophan in autoclave , is there a chance of having a false positive?

Free tryptophan is susceptible to degradation when exposed to heat, especially in the presence of oxygen. Studies show that when tryptophan is heated in air or oxygen, it undergoes degradation following first-order kinetics, indicating it is thermolabile under these conditions.

However, when tryptophan is heated in the absence of oxygen (e.g., under nitrogen), it is much more heat stable.

Protein-bound Tryptophan: When tryptophan is incorporated into proteins, its thermal stability increases. Protein-bound tryptophan remains stable under heat, particularly in oxygen-free environments, even when other reactants like glucose or starch are present.