Study of phenolic composition and antioxidant activity of myrtle leaves and fruits as a function of maturation

This is the first study about the influence of the maturation stage and of extraction processes on the phenolic content, radical scavenging properties and inhibition of cholinesterases by leaves and fruits (whole fruit, seeds and pericarp) of Myrtus communis. Ten phenolic compounds were identified by HPLC–DAD in six different plant materials, namely gallic acid, delphinidin-3-O-glucoside, myricetin-3-O-rhamnoside, quercetin-3-O-galactoside, quercetin-3-O-rutinoside, malvidin-3-O-glucoside, myricetin, ellagic acid, quercetin and kaempferol. All extracts exhibited a dose-dependent effect against DPPH, superoxide anion (O2●−) and nitric oxide (●NO) radicals. Leaves collected in September and December, ripe berries harvested in December and seeds from ripe berries were the most active ones, displaying IC50 values between 3.89 and 19.02, 24.19 and 34.69 and 13.69 and 76.01 μg/mL against DPPH, O2●− and ●NO, respectively. All plant parts were more active than ascorbic acid as radical scavengers against O2●− (IC50 = 372.85 μg/mL) and ●NO (IC50 = 248.25 μg/mL). Ripe berries and pericarps were the only parts containing anthocyanins, had the lowest amount of phenolic compounds (6.00–15.44 g/kg of dry extract) and were the least active ones. PCA analysis was performed to select the extracts with strong antiradical activity and possessing the highest amount of phenolic compounds (c.a. 50 g/kg of dry extract), to be further tested against cholinesterases; however, the selected seed extracts displayed weak inhibitory activity. This study demonstrates that the development stage of M. communis is a key factor to obtain and optimize a desired composition of phenolic antioxidants to be applied, for instance, as additives for the development of functional foods.