Phenolic Compounds, Antioxidant and Antimicrobial Activities of Punica granatum L. Fruit Extracts

TL;DR

Pomegranate pericarp extracts have higher antioxidant and antimicrobial properties than juice extracts, making them a valuable by-product for functional ingredients.

Contribution

This is the first comparative study of pomegranate juice and pericarp extracts from Montenegro and Italy, revealing their detailed phenolic profiles and bioactivity.

Findings

Pericarp extracts showed significantly higher antioxidant activity than juice extracts.

Pericarp extracts exhibited bactericidal effects against MRSA and other clinically relevant strains at low concentrations.

Ellagitannin punicalagin isomers were the most abundant phenolic compounds in the extracts.

Abstract

Pomegranate is valued for its abundant polyphenolic content and its capacity to promote health. In this study, pomegranate juice or pericarp extracts from two Mediterranean regions (Montenegro and Italy) were systematically and comparatively evaluated for the first time with respect to their polyphenolic composition, antioxidant capacity, and antimicrobial activity. The extraction of juice extracts was accomplished by means of the Kutscher–Steudel liquid–liquid extraction technique, which was employed to selectively recover phenolics. In contrast, the extraction of pericarp extracts from the solid matrix was achieved via Soxhlet extraction. A thorough high-performance liquid chromatography (HPLC) analysis was conducted to identify and quantify the major phenolic compounds present in the sample. This analysis revealed the presence of ellagitannin punicalagin isomers, with concentrations reaching up to 254.75 mg/g of the sample, as well as ellagic acid and gallic acid. The antioxidant potential of the samples was assessed using the antioxidant activity index (AAI) from the 2,2-diphenyl-1-picrylhydrazyl (DPPH) test and by a ferric reducing antioxidant power (FRAP) assay. Juice extracts demonstrated a range of activity levels, with AAI values ranging from 0.17 to 2.12 and FRAP values ranging from 2.49 to 19.41 mmol Fe2+/g. In contrast, pericarp extracts exhibited notably higher activity, with AAI values ranging from 0.18 to 27.57 and FRAP values ranging from 2.99 to 372.17 mmol Fe2+/g. This study demonstrates the markedly higher functional potential of pericarp extracts compared to juice extracts by linking detailed phenolic profiles with bioactivity data. Antimicrobial testing, inclusive of the determination of minimum bactericidal concentration (MBC), demonstrated that certain pericarp extracts manifested bactericidal properties at low concentrations against selected clinically pertinent strains, including methicillin-resistant Staphylococcus aureus (0.109% p/v), methicillin-sensitive S. aureus (0.109% p/v), carbapenem-resistant Acinetobacter baumannii (0.109% p/v), and Escherichia coli (0.563% p/v). Candida albicans and Klebsiella pneumoniae strains exhibited minimal sensitivity to these extracts. The findings indicate that pomegranate pericarp is a valuable by-product, and they demonstrate the potential of both juice and pericarp extracts as functional ingredients.