Antimicrobial and antioxidant features of 'Gabsi' pomegranate peel extracts

The work aimed at optimizing the extraction protocol of 'Gabsi' pomegranate peel (PP) and evaluating the total phenol content and profile, antioxidant activity and antimicrobial effect of the extracts obtained. Water and methanol as solvents were compared at different peel/solvent ratios; three different temperatures were also compared for the water extraction. Methanol pomegranate peel extract (MPPE) and water extracts (WPPE) were analysed for their DPPH antioxidant activity and polyphenol profile and content by HPLC/DAD and HPLC/MS. Different concentrations of MPPE and WPPE (ranging from 0.061 to 0.304 and from 0.072 to 0.361 g dry extract/mL, respectively) were also tested in vitro against Penicillium digitatum, Pseudomonas putida and Saccharomyces cerevisiae to determine the minimum inhibitory concentration (MIC). The MPPE and WPPE had comparable antioxidant activity (4081.43 and 3497.02 mmol Trolox/g, respectively). Hydrolysable tannins represented the main polyphenols in pomegranate peel, with punicalagin as the major compound. In general, MPPE dilutions tested in well-diffusion assays were more effective against targeted microorganisms compared with WPPE; indeed, only the highest WPPE concentration, was able to inhibit the growth of targeted microrganisms. Viability tests in liquid medium confirmed the highest antimicrobial capacity of MPPE, although even the WPPE was able to reduce P. putida and S. cerevisiae populations by up to 3.15 and 2.52 log CFU/mL, respectively.