Melatonin and its derivatives in red wine: contribution of fermenting microorganisms

Melatonin (MEL) is an indoleamine produced mainly by the pineal gland in vertebrates and it has a significant role in regulation of circadian rhythm, mitigation of sleeping disorder and jet lag. It has been found in medicinal plants, plant foods including seeds, fruits and fermented beverages, and, therefore, its occurrence in plants is now ascertained. In grapes and wines, MEL ranges from sub-ng/g to µg/g and from sub-ng/mL to ng/mL, respectively, with varying levels according to both endogenous and exogenous factors. In addition, MEL isomers and tryptophan-ethylester (TEE, a compound with the same molecular weight of MEL) have recently been detected in wine and the fermenting yeast plays an important role for their production [1]. It has been suggested that, in synergy with polyphenols, MEL in wine may contribute to maximize the health-promoting effects of Mediterranean diet. The research aimed to validate an analytical method for the simultaneous detection of MEL, TEE and tryptophan. The sample preparation was developed by means of SPE purification. Purified samples of synthetic wine solution (tartaric acid 5 g/L, ethanol 12% [v/v], pH 3.2) and red wine spiked with the analytes of interest were analyzed by liquid chromatography coupled with both fluorescence and mass spectrometry detectors. MEL, TEE and tryptophan were successfully detected and quantified by both the analytical conditions adopted. The response was linear for all the investigated compounds and it was comparable between synthetic wine solution and red wine. The recovery was higher than 85% and the relative standard deviation was lower than 10%. The developed method was applied for the analysis of red wine samples produced in a cold area of North of Italy. Preliminary results showed an increase of TEE concentrations suggesting the possible positive influence of secondary fermentations other than the alcoholic fermentation.