L-tryptophan is mostly used in the animal feed industry but it also has a number of food applications, including clinical nutrition and supplements designed for bodybuilders.
Current production is through fermentation however this method has been linked to safety issues in the past.
Supplements of the amino acid sold as a sleep aid (it is a precursor for serotonin) were removed from the US market in 1990 by the US Food and Drug Administration after they were linked to several thousand cases of the muscular disease eosinophilic-myalgia and a number of deaths.
Since then tryptophan, naturally present in dairy products, beef, poultry, brown rice, fish and soybeans, has only been permitted on the European market under special regulations for dietetic foods, called PARNUTS.
But demand for the ingredient in new applications has triggered interest in alternative manufacturing methods.
"We have received several requests over the past years [for this ingredient]," NIZO scientist Dr Kees Olieman told NutraIngredients.com.
NIZO was commissioned by Unilever to develop a small quantity of food-grade tryptophan for use in a diet beverage. It is thought that low intake of the amino acid may be responsible for mood swings that make it difficult for some people to stick to a weight-loss regime.
The NIZO team used the milk protein alpha-lactalbumin as the starting material for their new process. A-lactalbumin contains more tryptophan residues in its molecule than any other dairy protein.
"One of the key problems was to find a set of food-grade enzymes to hydrolyse alpha-lactalbumin sufficiently. The difficult part was that some peptide bonds close to tryptophan are quite resistant to enzymatic hydrolysis," noted Dr Olieman.
Scaling up the chromatographic isolation and the removal of the solvent after the chromatographic isolation of tryptophan posed further challenges, he said.
However the resulting product can be considered safer than one produced through fermentation.
"We start with food grade materials and use food-grade enzymes," explained Dr Olieman.
He added that the issue with l-tryptophan is not "so much the purity but the nature of the impurities. Food ingredients that are enriched with peptides containing tryptophan might fulfil equally well the needs [of the food industry]," he said.
The enzymes and conditions were tested in small-scale laboratory experiments, he added, and significant steps need to be taken before the process can be carried out on an industrial scale.
The global food industry currently only uses around 100-150 tons of the amino acid annually but there could be further demand as the weight-loss foods market grows.
Unilever declined to comment on its intended use of tryptophan but amino acids, already widely used in Japan, are seeing growing interest from Europe's food industry, with a number of new peptide-based ingredients launched last year.