Arbutus unedo L. berries have traditionally been used as edible and medicinal fruits in folk medicine for the treatment of some pathologies. Besides their good nutritional properties, these berries are rich in bioactive compounds. Accordingly, a HPLC-triple quadrupole (TQ)-MS/MS method was developed and validated for the first time to characterize the changes produced in the phenolic composition profile of A. unedo L. fruits through three ripening stages. Several hydroxycinnamic and

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... ic acids were detected, gallic acid being the highest phenolic acid quantified. Quercetin, quercetin-3-β-glucoside, rutin, and kaempferol were found in similar amounts at the different maturity stages. High amounts of (+)-catechin, procyanidin B2, epigallocatechin, and (−)-epigallocatechin gallate were observed in the unripe fruits. Naringin and vitexin were also quantified. Stilbenes, such as trans-resveratrol and trans-piceid, were identified for the first time in these fruits. Total phenolic compounds, total anthocyanin compounds, and radical scavenging activity were also determined in the fruits harvested at different years in several locations of the Iberian Peninsula at different ripening stages. The results confirmed that these fruits are an excellent source of these bioactive compounds (mainly flavanols) with high antioxidant activity, which could be used as a new source for preparation of nutraceutical or functional foods.