Formation of a 3-(phenylamino)alanine contaminant in EMS-associated L-tryptophan

Chemical studies were conducted to determine the origin of the 3-(phenylamino)alanine (PAA) contaminant in EMS-associated L-tryptophan samples. Anthranilic acid, a biosynthetic precursor of the L-tryptophan, was heated at 80°C for 6 h under acidic conditions to produce 140 μg of aniline/g of anthranilic acid. The presence of aniline was verified by HPLC-UV and GC-MS. PAA (160 μg of PAA/g of aniline) was produced by heating aniline and serine at 80°C for 6 h under basic conditions. PAA was confirmed by HPLC-UV and LC-MS. These results suggest that PAA could be formed under the fermentation and purification conditions used to produce L-tryptophan on an industrial scale.