**1. Introduction**

The neurohormone melatonin (MEL) (N-acetyl-5-methoxytyramine) is produced in the pineal gland and can be also found as metabolite in plants. Moreover, the synthesis of MEL derives from the aminoacid tryptophan, leading to 5-hydroxytryptophan, serotonin, and finally, N-acetylserotonin. Moreover, MEL can also be produced by *O*-serotonin methylation followed by N-methoxytryptamine acetylation by the action of yeast [1, 2].

MEL content has been reported in seeds, for example, rice or corn and roots, leaves, or fruits of a significant range of plants. The occurrence of MEL has also been reported in olive oil, especially in extra virgin olive oil, and in sunflower oil [3]. Moreover, the content of MEL has also been reported in grapes and wines [4]. Scientific literature has revealed that MEL is formed after fermentation with wine yeast, mainly due to *Saccharomyces cerevisiae* [5].

MEL is a key modulator of human health, showing antioxidant, anticarcinogenic, or neuroprotective capacity between others [6]. The biological capacity of their main metabolites as N-1-acetyl-N-2-formyl-5-methoxyquinuramine (AFMK) and N-1 acetyl-5-methoxyquinuramine (AMK) is also significant. AFMK is considered a potent antioxidant compound, and AMK is also a potent antioxidant being able to inhibit the biosynthesis of prostaglandins related to diazepam receptors [7]. As other secondary metabolites, MEL can promote antioxidant enzymes and/or neutralize free radicals [1]. In vivo studies have also reported the antioxidant capacity of MEL, which decreases chronic oxidative stress related to aging [8] and reduces blood pressure in men with chronic hypertension [9]. MEL has been successfully used for sleep disorders restoring circadian rhythm and is especially effective in population with neurodegenerative illnesses.

The amphipathic property of MEL allows it to cross some physiological barriers, being present in the cytosol, mitochondria, and different biological membranes [10]. Therefore, MEL provides biological properties where it is needed.
