Antimicrobial activity of phenolics isolated from the pruning wood residue of European plum (Prunus domestica L.)

European plum (Prunus domestica L.) is a tree cultivated in many countries for its edible fruits, and necessarily certain amounts of useless woody residues are generated every year during pruning works. The objectives of this research were to recover the phenolics present on that wood wastes and study their antimicrobial and antibiofilm activities against a selection of foodborne microorganisms, including multi-resistant strains. The isolation of components was carried out by combining fast centrifugal partition chromatography (FCPC) and semi-preparative high-performance liquid chromatography (HPLC), and the identification was achieved by conventional techniques. Nine compounds were identified: 2 flavan-3-ols [catechin (1) and epicatechin (2)]; 1 phenolic glucoside [annphenone (3)]; and 6 dimeric A-type proanthocyanidins (4–9). All of them have been reported in Prunus domestica by the first time in this work, with the exception of 1 and 2. Extracts, fractions and purified phenolics were submitted to antimicrobial and antibiofilm activity evaluations. The most significative antimicrobial effect was detected on the strain Enterobacter sp. UJA37p, previously isolated from organic tomato and with high tolerance to different biocides. All pure compounds showed MIC values of 100 μg/mL against this resistant bacterium. On the other hand, when bacteria were previously allowed to attach and form biofilm before treatments, we found interesting results in disruption of preformed biofilms with compound 7 [(+)-epiafzelechin-(2β→O→7,4β→8)-epicatechin], followed by compound 6 [(−)-ent-epiafzelechin-(2α→O→7,4α→8)-catechin] and compound 3 at a concentration of 0.1 μg/mL.