Improvement of the chelating capacity of sugarcane bagasse lignin through oxidation with polyphenoloxidase

Lignin obtained from Acetosolv pulping of sugarcane bagasse was oxidized by polyphenoloxidase (PPO)/O-2/glycerol to increase the number of carbonyls and hydroxyls in lignin, and to improve its chelating capacity. increase in the absorption in W-spectrum related to alpha-carbonylphenolic and alpha,beta-unsaturated structures was observed in all experiments. The chelating properties of original and oxidized lignins were compared by monitoring the amount of Cu+2 bound to lignin by gel permeation chromatography. The chelating capacity of original Acetosolv lignin was 354 mg Cu+2/g lignin. On the other hand, lignin oxidized with PPO/O-2 showed an increase in chelating capacity of 73% in relation to the original lignin. Lignin oxidized with PPO/O-2/glycerol showed a chelating capacity 110% higher than that of the original lignin. Glycerol stabilizes PPO, increasing its half-life time. Average molecular weight (Mw), measured by size-exclusion chromatography, was smaller for the oxidized lignins than for the original Acetosolv lignin. This result suggests that quinones can be eventually formed through the action of PPO but are not polymerized. The chelating capacity of oxidized lignins increases with the incorporation of vicinal hydroxyl groups.