Study of the Effects of the Water and Ethylene Glycol on Biomass Pretreatment Using a Deep Eutectic Solvent and Evaluation of the Antioxidant Activity of Lignins

Over the past few years, there has been a lot of interest in researching deep eutectic solvent (DES)-based biomass fractionation. However, the underlying mechanism is still not fully revealed due to the intricate interactions between DES components and lignocellulosic biomass. In this work, switchgrass, pine, corncob, and corn stalk were pretreated for 24 h at 130 °C with a well-known DES composed of choline chloride and lactic acid (1ChCl2LA) at a mole ratio of 1:2. 1ChCl2LA was mixed with water or ethylene glycol (EG) to assess their impact on the delignification ratio and enzymatic hydrolysis. Changes in biomass composition, biomass crystallinity, delignification, and saccharification were observed as a function of water or EG content, shedding light on the process of the DES-based pretreatment. Lastly, acetone was utilized to fractionate the lignins extracted from the biomasses after pretreatment. The antioxidant activity of these lignin fractions was measured, revealing two different interactions between lignin antioxidants.