Evolution of tryptophan and its foremost metabolites’ concentrations in milk and fermented dairy products

• Milk and dairy products provide the important amino acid tryptophan.
• Triptophan is a precursor of serotonin, which modulates gastrointestinal activity.
• Triptophan concentrations increase with fermentation.
• Dairy cultures might be exploited for tryptophan provision.

Milk and dairy products provide tryptophan (TRP), which is an essential amino acid with manifold biological roles such as contribution to the synthesis of proteins and other physiologically active metabolites. TRP is also a precursor of serotonin, which acts in the gastrointestinal system by mediating motor activity, secretion processes, and visceral sensitivity.In this study, we analyzed the concentrations of free TRP, 5-hydroxytryptophan, serotonin, tryptamine, and kynurenine in milks and fermented dairy products at packaging and at their expiration date. TRP concentrations and those of one of its major metabolites, i.e. 5-hydroxytryptophan increase with fermentation whereas those of kynurenine (which has been implicated in the onset of cardiovascular disease and in neurodegeneration) do not differ between milks and their fermented derivatives. Storage has no effect on tryptophan concentrations. The possibility to exploit tryptophan production by dairy cultures and formulate appropriate functional foods should be explored in the future.

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