Na2co3

The chemicals of 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox), 2,2’-azino-bis (3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS), 1,1-diphenyl-2-picryl-hydrazyl (DPPH), 2,4,6-tri(2-pyridyl)-S-triazine (TPTZ), Folin–Ciocalteu’s phenol reagent, and gallic acid and catechin were purchased from Sigma-Aldrich (St. Louis, MO, USA). The sodium acetate, ferric chloride, and Na₂CO₃ (> 99%) were purchased from Beijing Solarbio Technology Co., Ltd. (Beijing, China). The methanol (chromatographic grade grade) was obtained from Beijing Yishan Huitong Technology Co., Ltd. (Beijing, China). Milli-Q ultra-pure water was used for all experiments.

Soochow University (Suzhou, China) kindly provided SF aqueous stock solution. Briefly, SF fibers isolated from the cocoons of a Bombyx mori silkworm were boiled for 30 min in an aqueous solution of 0.02 M Na₂CO₃ (Solarbio). Subsequently, the fibers were rinsed thoroughly with distilled water to extract the glue-like sericin proteins. After air-drying, the degummed silk fibers were placed in a 9.3 M lithium bromide (Aladdin Bio-Chem Technology, Shanghai, China) solution in a glass beaker at 60°C for 4–5 h. Then, the solution was dialyzed against distilled water in a dialysis bag with a molecular weight cut-off of 3500 Da for 3 days. Finally, the solution was centrifuged, and the concentration was determined by weighing the residual solid of a known solution volume after drying at 60°C.