Extraction of lignin from sustainable lignocellulosic food waste resources using a green deep eutectic solvent system
Sayantan Ghosh1, Krishna Pramanik1
1Department of Biotechnology and Medical Engineering, National Institute of Technology, Rourkela 769008, Odisha, India.
Abstract:
Food waste, an abundant and widely available lignocellulosic biomass is a potential feedstock for recovering value-added products like lignin possessing various valuable properties through valorisation thereby minimizing its disposal and hence detrimental impact to the environment. The present study investigates the efficacy of the choline chloride-oxalic acid DES system for extracting lignin biomaterial from a variety of food wastes namely potato peel, onion skin, tea residues, banana peel and pomegranate peel wastes and its properties. The extraction experiments were carried out at 100°C for 6h using DES with a solid-to-liquid ratio of 1: 10 (w/v). The yield and purity of the extracted lignin from different biowastes were determined. A varied yield and purity of lignin was obtained depending on the sources of waste biomass. However, the highest lignin yield of 22.439 ± 4.38 % and purity of 77 ± 1.95 % was obtained with pomegranate peel. A comparable lignin yield (21.348 ± 2.40 %) and purity (75 ± 1.26 %) was also achieved with banana peel. UV-Visible and FTIR analyses revealed the existence of aromatic and major functional groups of lignin. XRD analysis confirmed its amorphous nature and its spherical or ellipsoidal morphology revealed by FESEM image analysis. The presence of hydroxyl ions, phenols, and carboxylic acids, and protons in the methoxy group and aliphatic and aromatic moieties in the lignin were identified by negative zeta potential values and 1H NMR spectra analysis respectively. The quantity of major linkages like β-O-4', β - 5' and β - β' in the lignin was determined by 2D-HSQC NMR. The lignin also exhibited antimicrobial and antioxidant activities. The elemental composition and higher heating values were determined by CHNSO analysis. Overall, pomegranate and banana peels are the most prospective food wastes found in this study for extracting lignin with high yield. The study further demonstrated the potentiality of the green DES for food waste valorisation to extract lignin.
