Extraction, isolation, characterization and antimicrobial activities of non-extractable polyphenols from pomegranate peel

Non-extractable polyphenols (NEPPs) in pomegranate peel were released by acid hydrolysis followed by extraction using ethyl acetate (EtOAc). Ten NEPPs were identified in the hydrolysate using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Six compounds were then isolated from the EtOAc extracts whose structures were identified as?-sitosterol-3-O-glycoside (1), ?-sitosterol (2), ursolic acid (3), corosolic acid (4), asiatic acid (5) and arjunolic acid (6) using a wide range of spectroscopic analyses. Compounds 4?6 were isolated for the first time from pomegranate peel. Antimicrobial experiments revealed that compound 3 and 5 showed significant antimicrobial activity against a range of pathogens, particularly compound 5 which exhibited selective inhibitive activity towards Staphylococcus aureus with a minimum inhibitory con-centration (MIC) of 16 ?g/ml. The present study has provided new insights into the composition of bound chemicals in pomegranate peel and laid a foundation for improving its further processing and utilization.

Automated summary

Non-extractable polyphenols (NEPPs) in pomegranate peel were released using acid hydrolysis and ethyl acetate extraction, leading to the identification of ten NEPPs. Six compounds were isolated and their structures determined, with compounds 3 and 5 showing significant antimicrobial activity. This study sheds new light on the composition of bound chemicals in pomegranate peel and serves as a foundation for further processing and utilization.