Melatonin and related bioactive compounds in commercialized date palm fruits (Phoenix dactylifera L.): correlation with some antioxidant parameters

The presence of melatonin in plant foodstuffs is a matter of growing interest since its antioxidant properties and the possible benefits for health of consumers. Fruits of date palm (Phoenix dactylifera, L.) are highly appreciated because of their nutritional value and healthy properties related to high content in antioxidant compounds present in them. In this study, we show that dates' antioxidant properties persist in several commercialized varieties typical of the European markets, as compared to values referenced from studies in date fruit varieties collected in the origin countries. We also show for the first time that melatonin and one of its isomers are present in dates, being that the isomer content is several times higher than melatonin (in the range of 1 mu g per 100g of fresh weight). The isomer content was highly correlated with total phenolic compounds and total antioxidant capacity in the date varieties. Additionally, high levels of the indoleamines, serotonin and auxin accumulate in dates, which could be related to fruit ripening. All the indole derivatives analyzed in dates exhibited antioxidant activity as assayed by DPPH, with differences among the compounds and concentrations used. These results support that melatonin, its isomer, and related indoles present in dates could contribute to the reported health benefits of this fruit by increasing its natural antioxidant potential.