Antioxidant Peptides from Tiger Nut (Cyperus esculentus L.): Chemical Analysis and Cytoprotective Functions on HepG2 and Caco-2 Cells

Tiger nuts were enzymatically hydrolyzed by Alcalase and then separated and purified by ultrafiltration classification and Sephadex G-15 fractionation to obtain tiger nut peptides. Their chemical antioxidant activities and cytoprotective functions on HepG2 and Caco-2 cells were systematically evaluated in this study. The tiger nut peptides (TNP) were found to perform excellent antioxidant activity supported by their chemical and cell antioxidant behaviors, amino acid composition, and morphological observation. Higher 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity (DPPH• RSA, 64.05-124.07%) and ferric ion-reducing antioxidant power (FRAP, 0.17-1.78 μmol/mL) were observed in the TNP with more hydrophobic amino acids (41.77 ± 1.36 g/100 g) compared with traditional soybean and peanut peptides. Furthermore, the peptides from tiger nut (TNP, TNP-4, T1, T2, T3) could effectively protect H₂O₂-induced HepG2 and Caco-2 cells from oxidative damage by enhancing endogenous antioxidant enzyme activities and reducing oxidative stress levels, especially the T3 peptides purified from the fraction less than 1 kDa molecular weight. The catalase, superoxide dismutase, and glutathione peroxidase activities significantly increased, and the contents of intracellular reactive oxygen species and malondialdehyde decreased. This study highlights the potential of the peptides from tiger nuts as antioxidant ingredients for food applications.