One-step process based on the order of hydrothermal and alkaline treatment for producing lignin with high yield and antioxidant activity

Three one-step processes based on the order of hydrothermal (170 degrees C, 30 min) and alkaline treatment (2% NaOH, 90 degrees C, 120 min) have been proposed for the production of lignin from wheat straw. The yield, purity, dissociation mechanism, structural transformation, and antioxidant activity of the lignins obtained from the various processes were systematically investigated. It was found that the order of hydrothermal and alkaline treatments had significant effects on the structural features and antioxidant activities of lignins. Hydrothermal process facilitated the subsequent alkaline delignification, releasing lignins with the highest yield (90.3%) and purity (97.4%). The beta-O-4 linkages were obviously cleaved during the hydrothermal treatment, which resulted in an increase content of phenolic OH groups. The types and content of phenolic OH groups in lignins were closely related to its antioxidant properties. The lignins released during the one-step process based on successive hydrothermal and alkaline treatment had a high yield and antioxidant activity and the process would be very beneficial to the industrial production of potential antioxidant for food oils and fats, as well as food preservative that prevent the loss of food flavour.