Almost a year ago, The Academic Wino presented an article that examined the role of melatonin in grapes. Results of that study found that melatonin fluctuates in the grape vine and grapes during the day, and that in order to create a wine with higher levels of melatonin, one must harvest the grapes at an optimum time. One thing this article did not examine was the levels of melatonin in wine itself, and whether or not these levels would be detectable in the finished wine after going through the winemaking process.
Melatonin is a compound found in many life forms that is synthesized from L-tryptophan metabolism via serotonin (think “turkey coma”) and is considered both an antioxidant and a compound that aides in regulating circadian rhythms. In humans (and other vertebrate species), melatonin is synthesized by the pineal gland and secreted into the blood stream. Melatonin tends to be highest in younger humans/vertebrates, and decreases with age. Melatonin is also found in the leaves, fruits, and seeds of plants, the purpose of which is not entirely understood, but some have speculated is a defensive mechanism against UV light exposure.
Up until recently, melatonin has been found in about 8 grape varieties, though only one study so far has identified melatonin in wine. The short study presented today aimed to determine whether or not melatonin was present in wine from different grape varieties and to test a few different analytical methods for efficiency and accuracy.
Wines used in this study were made at the Instituto de Investigación y Formación Agraria y Pesquera in Jerez de la Frontera, Spain. Grapes were harvested in 2007 at maturity and underwent controlled winemaking procedures at 25oC. Grape varieties harvested were: Cabernet Sauvignon, Jaen Tinto, Merlot, Palomino Negro, Petit Verdot, Prieto Picudo, Syrah, and Tempranillo. All wines made were single varietal.
Methods used for analyzing melatonin levels were: ELISA, LC-fluorescence, and LC-ESI-MS/MS.
Eight single varietal wines were analyzed in duplicate by ELISA, and triplicate by all other methods.
- ELISA analysis indicated that Palomino Negro possessed the highest levels of melatonin out of all wines analyzed.
- Cabernet Sauvignon, Jaen Tinto, Merlot, Petit Verdot, Prieto Picudo, and Syrah all showed similar levels of melatonin, which ranged from 162pg/mL to 230pg/mL.
- Due to the complexity of the wines, which contain many primary and secondary metabolites, these compounds can interfere with ELISA results, creating false positives or false negatives when there may or may not be present the compound of interest.
o Results indicated a 25% false positive rate and a 28.6% false negative rate.
o These results suggest that ELISA is a poor method for analyzing melatonin in wine, since results were unclear and inaccurate.
- Unlike ELISA, the LC-Fluorescence method was reliable for analyzing melatonin levels in wine.
o For Trebbiano wines, the melatonin level determined by LC-Fluorescence was 0.04ng/mL.
- LC-MS/MS analysis showed that Tempranillo wines contained the highest levels of melatonin.
o Cabernet Sauvignon, Petit Verdot, Prieto Picudo, and Syrah all had markedly variable levels of melatonin.
o Melatonin was not found to be present in Jaen Tinto, Merlot, and Palomino Negro wines.
- LC-MS/MS analysis showed that isomers of melatonin (same molecular formula, but different structure) were found in highest levels in Jaen Tinto wines (32.6ng/mL).
o ¼ of the melatonin found in Tempranillo wines was in its isomeric form.
o Small amounts of melatonin isomer were found in Cabernet Sauvignon, Merlot, Palomino Negro, Prieto Picudo, and Tempranillo.
o There were no melatonin isomers found in Petit Verdot or Syrah.
- The presence of melatonin in wines was quantitatively and qualitatively extremely diverse.
- Melatonin in wines was present in its functional form and also in its isomeric form in wines, the levels of which varied greatly depending upon varietal of wine.
- Melatonin and melatonin isomer levels may be a function of grape variety and winemaking techniques.
The results of this study were simple in that melatonin is present in wines, though is specific to varietal and potentially winemaking technique. Levels of melatonin in wines are also highly variable, again due to varietal, winemaking technique, and the method used to collect the data. According to the results of this study, LC-MS/MS was the best method for determining levels of melatonin in wines, though further analysis would need to be done to ensure repeatability.
So what does it mean if there is melatonin present in wine? Well, I (and science!) am not 100% sure, but since it often functions as an antioxidant, it would likely join the ranks of the other polyphenols, flavanols, and resveratrol that have all been shown to have incredibly positive health benefits. Melatonin has been so little studied in wine that it is difficult to determine what other, if any, health benefits it may have in wine. Are the levels of melatonin present in wine enough to even elicit these health benefits? There have been no clinical trials focusing on this compound as a function of its health benefits when in wine, so it is hard to say.
I’d love to hear what you all think about this topic. This study leaves much to be determined, so I’d love to hear how you all interpret these data and how you extrapolate this to real world functionality.
Please feel free to comment below!
Source: Rodriguez-Naranjo, M.I., Gil-Izquierdo, A., Troncoso, A.M., Cantos, E., Garcia-Parrilla, M.C. 2011. Melatonin: A new bioactive compound in wine. Journal of Food Composition and Analysis 24: 603-608.
I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!