Optimization of Extraction of Lignin as a Value-Added Product from Pomegranate Peel Bioresource Using a Green Solvent System

Abstract

The present work investigated the efficacy of a green deep eutectic solvent (DES) for the extraction of lignin from pomegranate peel as a potential bioresource and optimizing the extraction parameters for improving its yield. To this end, DES comprising of choline chloride and oxalic acid was used for extraction. The yield and purity of lignin were 22.44±4.38% and 77±1.95% and the extracted lignin was comprehensively characterized. UV-visible and Fourier Transform Infrared Spectroscopy analyses confirmed the existence of aromatic and key functional groups of lignin. The amorphous characteristic of lignin was evident from X-ray diffraction analysis, whereas the Field Emission Scanning Electron Microscopy image analysis revealed its desired ellipsoidal or spherical morphology. CHNSO analysis was conducted to determine the elemental composition and assess the heating value of lignin. The presence of phenols, carboxylic acids, and hydroxyl ions was identified by zeta potential and the thermal stability was evaluated using Differential Scanning Calorimetry. The existence of protons in the methoxy groups and in the aromatic and aliphatic regions of lignin, was identified through 1H Nuclear Magnetic Resonance (NMR) spectroscopy, while the quantity of major linkages was analyzed using Heteronuclear Single Quantum Coherence NMR. The extracted lignin exhibited superior antioxidant and antimicrobial activities than commercial lignin. DES demonstrated consistent extraction efficiency during three cycles of lignin recovery. The lignin yield was further improved to 41.67% by optimizing the extraction parameters using response surface methodology. The study demonstrated that DES is efficient in extracting lignin from pomegranate peel, thereby offering a sustainable approach to food waste management.