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Several studies have shown the presence of melatonin and related compounds in grapes and wines. The latter provides evidence of the possibility to enhance the nutraceutical properties of premium wines. However, there are many external factors that can influence the levels of this indolamine in grape and wines. In this study, the monitoring of melatonin and its tentatively identified isomer was carried out during the entire winemaking process in Vitis vinifera cv. Malbec by ultra high-performance liquid chromatography-tandem mass spectrometry. Laboratory and pilot studies were carried out to elucidate the role of grape, yeasts, and tryptophan in the evolution of the indolamines during the fermentation process. Melatonin was detected in grape extract within the range 120-160 ng/g while its isomer was found in musts and finished wines. Our results demonstrate that Saccaromyces cervisiae plays a decisive role in contributing to the content of melatonin and its isomer in wine.

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Melatonin (MT) presence in higher plants was recently discovered and the knowledge of its function in vivo is limited. Several studies have recently shown the occurrence of MT and related compounds in grapes and wines. The analysis of MT in plants and foods represents a highly challenging task due to its wide concentration range, the difficulty in the selection of the extraction solvents because of its amphipathic nature, and the fact that it reacts quickly with other matrix components. Thus, sample processing factors; preparation/cleanup procedures; and chromatographic/detection parameters, such as HILIC and reverse phase (C(8) and C(18)) chromatographic modes, ESI, and atmospheric pressure chemical ionization (APCI) in both negative and positive modes were evaluated. Taken together, we have demonstrated that optimal conditions were quite different for each of the matrices under study. A sonication-mediated extraction step was necessary for grape skin (100% v/v methanol) and plant tissues (50% v/v methanol), while wine and must required a SPE preconcentration step. HILIC-(+) APCI ionization was better for MT standards, while C(8) -(+) APCI was the best choice for grape skin and C(18) -(+ESI) was suitable for wine. On the other hand, C(8) -(+)ESI was the most appropriate for vegetal tissues of Arabidopsis thaliana. Proposed methods were validated and the LODs were in the low picogram levels range. The optimized approaches were applied to the determination of MT and its isomer in different vegetal/food samples; levels found within the range: 4.9-440 ng/g.

Natural deep eutectic solvents (NADES) is one of the hottest issues in the field of green chemistry. However, it is possible to make them greener? Herein we propose a new microwave (MW) assisted preparation demanding only seconds. The MW‐NADES were challenged with those obtained by the classical Heating & Stirring procedure in terms of green analytical metrics and physical parameters. Indeed, the following analytical applications were tested: a) extraction media for phenolics and alkaloids from plant, b) enhancers for electrochemical detection of phenolic compounds. Our results demonstrate outstanding environmental advantages as the dramatic decrease of synthesis time (the shortest time to date, 60 minutes to 20 seconds) and energy consumption (650 times lower). The analytical performance and physicochemical parameters were comparable with the traditional NADES.