Valorization of Punica granatum (pomegranate) peels: a case study of circular bioeconomy

Pomegranate peel (PP) constitutes 40-50 % of the total weight of the pomegranate fruit, thereby accounting for the peel waste nine times as compared to the quantity of fruit processed, thus posing the challenge of solid waste management. Sustainable management of PP through circular bioeconomy can be done by applying resource life-extending strategies. The present work uses this concept and reports valorization of PP with zero waste using the biorefinery approach. High-value products like polyphenol and dietary fibers were recovered sequentially from PP using greener deep eutectic solvents (DESs). PPs were initially treated with eleven adaptable DESs for the extraction of polyphenols using choline chloride (ChCl) as a hydrogen bond acceptor (HBA) and ethylene glycol (EG), glycerol (Gly), malic acid (MA), and urea (U) as hydrogen bond donors (HBDs). Furthermore, based on the total phenolic contents (TPCS), four DESs with the best (ChCl:EG (1:2) and ChCl:Gly (1:3)), intermediate (ChCl:MA (1:1)), and the least (ChCl:U (1:2)) efficiency were selected for characterization (FTIR and viscosity) and detailed evaluation for maximum extraction of TPC. The obtained extracts were subjected to qualitative/quantitative test (LC-MS/MS) to assess the presence of phytochemicals/six phenolic acids along with the antioxidant (ferric-reducing antioxidant power/ABTS assay) and antibacterial (Escherichia coli and Staphylococcus aureus) ability. The PP and its residues were subjected to SEM and CHNS analysis and depicted structural variations proving DES to be an effective solvent for dissolving the cell wall. The residue obtained after extraction was analyzed for the total dietary fibers (51.08-41.92 %) to ensure the complete usage of the PP with zero waste.