Effect of drying pretreatment methods on structural features and antioxidant activities of Brauns native lignin extracted from Chinese quince fruit

Chinese quince is one kind of crop that has edibility and historical medical applications. However, the high amount of lignin makes processing Chinese quince fruit difficult; on the other hand, this lignin represents a valuable resource if a way of using it in industrial applications could be found. In this study, the structural features and antioxidant activities of Brauns native lignin (BNL) isolated from Chinese quince fruit after oven drying (60 °C, 75 °C, and 90 °C), sun drying, freeze-drying, and subcritical dimethyl ether drying were assessed. The BNL samples had low molecular weights (Mw, 2604–5511 g/mol), high carbohydrate content (6.10–9.95 %), and high phenolic OH content (1.76–2.29 mmol/g). NMR spectra showed that the BNL is of the SGH-type with the relative content of p-hydroxyphenyl units ranging from 13 to 21 %. Oven drying (90 °C) reduced the carbohydrate content and increased the phenolic hydroxyl content. Freeze-drying reduced the relative content of β-O-4′ linkages and increased the H-unit content. In terms of antioxidant activities, all samples possessed high DPPH free radical scavenging capacity (IC50, 0.12−0.22 mg/mL) and strong reducing power. These results indicate that BNL extracted from Chinese quince fruit is a promising source of natural antioxidant and biomass material.