Melatonin levels, determined by HPLC-ESI-MS/MS, deeply fluctuate during the day in Vitis vinifera cv Malbec. Evidences of its antioxidant role.

BOCCALANDRO, HE; GONZÁLEZ, CV; WUNDERLIN, D; BOTTINI, R; SILVA, MF

Montevideo, Uruguay

Congreso; XII Congreso Latinoamericano de Viticultura y Enología; 2009

Soc. Enologia y Viticultura Uruguay

Melatonin (MT), the often called ‘hormone of darkness’ is an ubiquitous molecule widely distributed in nature, produced by unicellular organisms, fungi, plants and animals. In animals the most prominent function is coordinating circadian and photoperiodic responses, but also as an effective antioxidant, presenting inhibitory effects on some cancer forms and inducing beneficial effects on neuronal disorders. Recent finding of melatonin in red wines opens an interesting perspective associated to the plethora of health benefits related to the moderate consumption of red wine. In plants, it has been speculated that MT protect them from intrinsic and environmental oxidative stress and that could play a role controlling flowering, but the long way to elucidate its physiological role in plants is beginning to be walk. The objectives of this work were: a) to study if MT levels and oxidative damage fluctuate during the day in berry skins of Vitis vinifera cv Malbec and whether they is any correlation between them, b) to determinate whether daylight reaching clusters controls MT level, as occurs in animals and c) to evaluate whether total polyphenols and anthocyanins accompanied MT fluctuation at harvest, with the end to find a moment of the day where high concentration of these valuable components of the wine coexist. Berry samples were collected during a whole day (April 26th 2008), in a commercial vineyard of Catena Zapata Winery, located in Valle de Uco (1.500 m a.s.l.), Mendoza, Argentina. Melatonin determination was performed by HPLC-ESI-MS/MS. As indicator of oxidative stress we measured MDA (malondialdehyde), a product of lipid peroxidation. We detected MT in berry skins at night (10,9 and 8,9 ng.g-1 at 2.5 and 6h respectively) reaching a strong peak at dawn (158,9 ng.g-1 at 9.5h). After this peak, MT levels deeply decayed to undetectable values (noon and afternoon). To asses whether MT content depletion during the day was triggered by light we measured MT level in covered (with a black sheet of EVA) and uncovered clusters. Covered cluster presented significantly higher (14.2 ng.g-1) MT levels than those exposed to natural radiation (N/D) in the afternoon, revealing that light was, at least, partially necessary to diminish MT levels during the day. Polyphenols and antocyanins did not fluctuate during the harvest day. We found an important fluctuation of MDA levels during the day, reaching a maximum at 17.5h (when temperature reached a maximum). Minimum MDA content was coincident with the moments of the day where MT was detected, suggesting a negative relation between MDA and MT. Preliminary data of exogenous applications of MT on bunches shown that higher MT levels decreased MDA content in berry skins, supporting it could play an antioxidant role. Summarizing, our results are the first showing a melatonin fluctuation: a) in plants growing under natural conditions, b) in a fruit organ and c) in the specie Vitis vinifera. We also provide evidences supporting its antioxidant role in grapes. As MT levels were high early in the morning, and polyphenols and anthocyanins did not vary during a day at harvest, we predict that wines confectioned with berries harvested at night or early in the morning will posses  higher nutraceutic properties due to its elevated MT content.