Phenolic Constituents of Pomegranate Peels (Punica granatum L.) Cultivated in Oman

Aims: This study was undertaken to analyze total phenolics and total flavonoids contents; and total antioxidant capacity of pomegranate peel extract and to identify the major functional components in the extract.

Study Design: The extract was subjected to ESI-MS/MS.

Place and Duration of Study: Department of Food Science and Nutrition, Sultan Qaboos University and DARIS Research Center, University of Nizwa, between December 2011 and August 2012.

Methodology: Pomegranate peel extract was analyzed using a Waters Quattro Premier XE tandem quadrupole mass spectrometer (Waters Corporation, Manchester, UK) equipped with electro-spray ionization (ESI) source. Instrument control and data acquisition were performed using Mass Lynx ver. 4.1 software. The instrument was calibrated for nominal resolution for MS1 and MS2 up to 1200 m/z using the sodium caesium iodide standard calibration solution.

Results: Results revealed high contents of total phenolics (64.2 mg Gallic acid equivalent/ g dry solids) and total flavonoids (1.4 mg Catechin equivalent/ g dry solids) respectively. Total antioxidant capacity ranged from 42.3 – 461.2 µmolTrolox equivalent/ g dry solids. The analysis revealed the presence of 61 different polyphenols in the extract among which 12 hydroxycinnamic acids, 14 hydrolysable tannins, 9 hydroxybenzoic acids, 5 hydroxybutanedioic acids, 11 hydroxy-cyclohexanecarboxylic acids and 8 hydroxyphenyls. Major compounds were tannins and flavonoids such as; illogic acid, gallic acids, punicalin, and punicalagin.

Conclusion: A wide variety of phytochemicals present in pomegranate peel extract were identified. These functional compounds in pomegranate peels could be utilized by the food industry and pharma/nutraceutical’s industry. Further work should be done to isolate and quantify major functional compounds of pomegranate peels such as ellagic acid.