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 (M w ) 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 M w 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 M w exhibited the strongest antioxidant activity (IC 50 = 28.8 μg/mL), which was even stronger than the commercial antioxidants BHT (3,5-di-tert-butyl-4-hydroxytoluene, IC 50 = 38.2 μg/mL) and BHA (3-tert-butyl-4-hydroxyanisole, IC 50 = 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.
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