Changes in the levels of indoleamine phytochemicals during veraison and ripening of wine grapes

Melatonin and serotonin have previously been described in mature wine grapes and finished wines, but the metabolism of these signalling molecules in the development of wine grapes has not previously been investigated. We harvested wine grapes at different stages of development from lag phase through veraison from eight different commercial vineyards representing a diversity of growing conditions, management practices, merlot varietals and localized ecosystems to determine whether different patterns in melatonin and serotonin can be found in wine grapes during seed development and berry maturation. Melatonin was detected in 45% of the fully developed purple, postveraison grapes but only found in 23% of prelag phase samples. However, the actual concentration of melatonin was highest in wine grapes harvested at the early stage of veraison when the seed is developing. Serotonin was not detected in any of the prelag phase grapes but was consistently detected in 30-35% of grapes harvested during the veraison transition at consistent levels of about 8-10 mu g/g. Interestingly, the nitrogen storage compound gamma-aminobutyric acid was also found at about 115 mu g/g in 77% of early stage green grapes and declined in both prevalence and concentration with ripening. Together, these data are indicative of a potential role for these molecules in the development and maturation of wine grapes.