In order to utilize lemon seed resources effectively , the antioxidant activities of its protein and enzymolysis peptide were studied. Lemon seed protein(LSP) was extracted from lemon seed meal powder with the alkaline extraction and acid precipitation. Response surface methodology was used to optimize the extraction process of LSP and analyze its amino acid composition. Papain, trypsin, compound protease and flavor protease were applied on the enzymatic hydrolysis of LSP. The antioxidant capacity (scavenging capacity of 1,1- diphenyl -2- picrylhydrazyl radical (\begin{document}$\mathrm{D}\mathrm{P}\mathrm{P}\mathrm{H}\cdot$\end{document}), hydroxyl radical(\begin{document}$\cdot \mathrm{O}\mathrm{H}$\end{document}) and superoxide anion(\begin{document}${\mathrm{O}}_{2}^{-}\cdot$\end{document})) of the enzymatic hydrolysate was studied, and the infrared spectrum analysis of the above four enzymatic peptides was carried out. The results showed that, the optimum extraction conditions of LSP were as follows: pH was 10.5, extraction time was 60 min, liquid-to-material ratio was 41:1 mL/g, and extraction temperature was 40 ℃. Under these conditions, the actual extraction rate of protein from lemon seed reached 12.25% ± 0.01%. The essential amino acids of LSP were complete in variety, accounting for 31.8% of the total amino acids. The flavor protease-hydrolyzed peptide had strong antioxidant capacity. The IC50 of papain enzymolysis peptide, trypsin-hydrolyzed peptide, peptide of compound protease and peptide of flavourzyme against DPPH free radical scavenging was 3.54, 1.75, 1.52 and 1.02 mg/mL, respectively. The IC50 against \begin{document}$\cdot \mathrm{O}\mathrm{H}$\end{document} free radical scavenging was 8.77, 8.92, 8.29 and 5.02 mg/mL, respectively. The IC50 against \begin{document}$\cdot \mathrm{O}\mathrm{H}$\end{document} free radical scavenging was 2.70, 0.90, 0.97 and 0.81 mg/mL. Theinfrared reflectance spectroscopy analysis suggested that all four samples had absorption peaks near 3400, 1600, 1300, and 1000 cm-1, and contained functional groups with antioxidant activity. The study considered that LSP had high antioxidant activity and nutritional value, and could be used as a functional component in the development of antioxidant-related functional foods and health care products.
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