title: Natural deep eutectic solvent mediated pretreatment of rice straw: bioanalytical characterization of lignin extract and enzymatic hydrolysis of pretreated biomass residue.
abstract: The present investigation demonstrated pretreatment of lignocellulosic biomass rice straw using natural deep eutectic solvents (NADESs), and separation of high-quality lignin and holocellulose in a single step. Qualitative analysis of the NADES extract showed that the extracted lignin was of high purity (>90 %), and quantitative analysis showed that nearly 60 ± 5 % (w/w) of total lignin was separated from the lignocellulosic biomass. Addition of 5.0 % (v/v) water during pretreatment significantly enhanced the total lignin extraction, and nearly 22 ± 3 % more lignin was released from the residual biomass into the NADES extract. X-ray diffraction studies of the untreated and pretreated rice straw biomass showed that the crystallinity index ratio was marginally decreased from 46.4 to 44.3 %, indicating subtle structural alterations in the crystalline and amorphous regions of the cellulosic fractions. Thermogravimetric analysis of the pretreated biomass residue revealed a slightly higher T dcp (295 °C) compared to the T dcp (285 °C) of untreated biomass. Among the tested NADES reagents, lactic acid/choline chloride at molar ratio of 5:1 extracted maximum lignin of 68 ± 4 mg g(-1) from the rice straw biomass, and subsequent enzymatic hydrolysis of the residual holocellulose enriched biomass showed maximum reducing sugars of 333 ± 11 mg g(-1) with a saccharification efficiency of 36.0 ± 3.2 % in 24 h at 10 % solids loading.
authors.affiliation: Bioconversion Technology Division, Sardar Patel Renewable Energy Research Institute, Post box No. 2, near BVM Engineering College, Vallabh Vidyanagar, 388 120, Gujarat, India. kiranbio@gmail.com.
authors.forename: Adepu K
authors.initials: AK
authors.lastname: Kumar
authors.affiliation: Bioconversion Technology Division, Sardar Patel Renewable Energy Research Institute, Post box No. 2, near BVM Engineering College, Vallabh Vidyanagar, 388 120, Gujarat, India.
authors.forename: Bhumika S
authors.initials: BS
authors.lastname: Parikh
authors.affiliation: Thermochemical Conversion Technology Division, Sardar Patel Renewable Energy Research Institute, Post box No. 2, near BVM Engineering College, Vallabh Vidyanagar, 388 120, Gujarat, India.|Science and Engineering Research Board, Department of Science and Technology, Government of India, Vasant Kunj, New Delhi, 110 070, India.
authors.forename: Mohanty
authors.initials: M
authors.lastname: Pravakar
mesh_terms: D018533:Biomass; D002480:Cellulase / Q000378:metabolism*; D006868:Hydrolysis; D008031:Lignin / Q000737:chemistry* / Q000378:metabolism*; D012275:Oryza / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D012997:Solvents; D008031:Lignin; D002480:Cellulase
keywords: Enzymatic saccaharification; Holocellulose; Lignin; Lignocellulosic biomass pretreatment; NADES; Rice straw