Antioxidant Activity of Lignin from Kraft Black Liquor Substance Eucalyptus Wood

Abstract

Kraft black liquor is produced from kraft process as byproduct. Lignin is the highest component in this black liquor, approximately 46% of the total solid. Lignin can be isolated from black liquor by precipitation using H2SO4 20% (w/v) until pH of 2. Klason method was used to purify lignin through hydrolysis using H2SO4 72% (w/v) to eliminate polysaccharides. The observed parameters were yield, molecular weight, phenolic hydroxyl content, functional groups analysis by infrared spectrophotometer, and testing the antioxidant activity of lignin. The phenolic hydroxyl content of 2.40%, respectively. Vibration of aromatic ring and deformation of C-H indicated that qualitatively lignin was present. Antioxidant activity of lignin was tested with DPPH method (1,1-diphenyl-2-picrylhydrazyl) as a free radical, measured using UV-Vis spectrophotometer at wavelength 515 nm. BHT (buthylated hydroxyltoluene) was used as a positive control. Percentage inhibition was plotted as a lignin concentration function. From the resulting graph can be determined lignin concentration required to reach 50% of percentage inhibition as the IC50. The IC50 was 43 ppm, which is less than 50 ppm, meaning that the eucalypt kraft lignin is potential as an antioxidant.