Enhancing Antioxidant Performance of Lignin by Enzymatic Treatment with Laccase

The utilization of lignin is of high interest since it represents the most abundant polyphenol worldwide. For the application of lignin as a natural antioxidant more phenolic hydroxyl groups (Ph–OH) and lower molecular weight (Mw) are essential. Here, we proposed a green method based on enzymatic treatment of two lignins (alkaline lignin AL and hydrolysis lignin HL) with laccase, by which the structure, especially the Ph–OH contents and Mw of lignin, could effectively controlled. The antioxidant activity of the lignin was evaluated in vitro by DPPH• (1,1-diphenyl-2-picrylhydrazyl) radical scavenging ability. The mechanism of antioxidant activity improvement was also elucidated. As expected, the enzymatic treated lignin (HL-L1.0) with the highest Ph–OH content and lower Mw exhibited the strongest antioxidant activity (IC50 = 28.8 μg/mL), which was even stronger than the commercial antioxidants BHT (3,5-di-tert-butyl-4-hydroxytoluene, IC50 = 38.2 μg/mL) and BHA (3-tert-butyl-4-hydroxyanisole, IC50 = 56.3 μg/mL). This study suggested that the enzymatic treatment was a green and effective way to obtain lignin derivatives that showed great potential for antioxidant applications.