Characterization of changes of lignin structure in the processes of cooking with solid alkali and different active oxygen

► The H2O2 and O2 have different effects on delignification when combined with MgO. ► The reactivity of the syringyl units is different in the two cooking processes. ► The decomposition of the β-O-4′ structures is also different in the two methods. ► A novel guaiacyl unit is generated only in the cooking with MgO and O2.