**2. Materials and Methods**

#### *2.1. Materials and Reagents*

Walnut kernels were purchased from the local market in Baoshan, China, 2,2- -azobis (2-amidinopropane) dihydrochloride (AAPH), 2,4-dinitrophenylhydrazine (DNPH), 5,5'- Dithiobis-(2-nitrobenzoic acid) (DTNB) and 8-Anilino-1-naphthalenesulfonic acid (ANS) were bought from Sigma-Aldrich Co. LLC. (Shanghai, China), and double antibody sandwich ELISA Kits was bought from Shanghai Meilian Biotechnology Co., Ltd. (Shanghai, China). All other reagents used were analytically pure, and water was distilled water in this study.

#### *2.2. Walnut Protein Isolates (WPI) Preparation*

WPI was extracted by the alkali dissolution-acid precipitation method according to Qin et al. [9] with slight modifications. Walnut kernels were pulverized and degreased with six-fold volumes of hexane three times. After being dried in a fume hood at room temperature, 25-fold volumes of sodium hydroxide solution (pH 8.7) were added to the defatted walnut powder, stirring the extract for 1 h at 48 ◦C, followed by centrifugation at 10,000× *g* for 20 min. The supernatant was adjusted to pH 5, and centrifuged using the same conditions as described above. WPI was obtained by washing the precipitate with H2O until neutral and freeze-drying it at −80 ◦C for 24 h. The WPI samples were stored frozen at −80 ◦C for spare use.
