Improving antioxidant activities of water-soluble lignin-carbohydrate complex isolated from wheat stalk through prolonging ball-milling pretreatment and homogeneous extraction

Water-soluble lignin-carbohydrate complex (LCC) rich in polysaccharides exhibits benign in vitro antioxidant activities and distinguishes high biocompatibility from lignin-rich LCC and lignin. However, the antioxidant activity of water-soluble LCCs remains to be improved and its structure-antioxidant relationship is still uncertain. Herein, structurally diversified water-soluble LCCs were isolated under different ball-milling pretreatment durations (4, 6, 8 h), extraction pathways (homogeneous and heterogeneous), and isolation routines (water extracts and residues after water extraction). Their structures were characterized by wet chemistry, chromatography and spectroscopies. Antioxidant activities were evaluated by ferric reducing antioxidant power and 1,1-diphenyl-2-picrylhydrazyl radicals scavenging rate (RDPPH). Results show that altering ball-milling duration and isolation procedures causes varied structures and antioxidant activities of the water-soluble LCCs. Specifically, prolonging ball-milling duration to 8 hours and homogeneous extraction can enhance their antioxidant activity through releasing more phenolic structures and promoting the extraction of high-molecular-weight LCCs via reducing mass-transfer resistance, respectively. As a result, the RDPPH of water-soluble LCCs reaches up to 97.35%, which is associated with the arabinan content with statistical significance (P < 0.05). This study provides new insights into the structure-antioxidation relationship of herbaceous LCC as potential antioxidants.