Antioxidant Properties of Sour Cherries (Prunus cerasus L.): Role of Colorless Phytochemicals from the Methanolic Extract of Ripe Fruits

Many edible plant metabolites are known to be useful as cellular antioxidants. In the search for antioxidative chemicals from native fruits of the Campania region of Italy, Prunus cerasus L., an acidic cherry widely used for culinary purposes, has been studied. Fruit crude extracts (MeOH, EtOAc, and hexane) were submitted to an antioxidative screening using specific assay media characterized from the presence of highly reactive radical species (DPPH•, ABTS•+, O2•−, NO) or lipoperoxidation markers. The reducing power of the samples was also determined. It was observed that the most polar extracts in MeOH and EtOAc were able to exercise a massive and dose-increasing antioxidative capacity. The peculiar efficacy of the same extracts was revealed by investigating their protein and deoxyribose oxidation capacity. A preliminary analysis of total phenol, flavonoid, and anthocyanin contents together with biological screening data put the basis on P. cerasus fruit phytochemical investigation of methanolic extract. Twenty secondary metabolites were isolated and characterized by spectroscopic (especially 1D and 2D NMR) and spectrometric techniques. 1-(4-Hydroxyphenyl)-1,2-ethanediol-1,2-bis-1-O-β-d-glucopyranoside (3), (4-hydroxy-3-methoxyphenyl)methanol-1-O-β-d-gentiobioside (4), epicatechin-3-malate (14), and epicatechin-3-(1′′-methyl)malate (15) were isolated for the first time. All of the compounds were evaluated for their radical scavenging activity on DPPH•, O2•−, and NO. Flavonoids and quinic acid derivatives were found to be the more antioxidative substances.