Structural and physicochemical characteristics, stability, toxicity and antioxidant activity of peptide-zinc chelate from coconut cake globulin hydrolysates

Three novel peptides Thr-Gly-Leu-Leu, Tyr-Ile-Leu-Ile-Lys and Phe-Asp-Glu-Glu of no toxicity were identified in coconut cake globulin hydrolysates. FDEE of excellent zinc-chelating capacity (30.80 mg/g) was selected for preparation of peptide-zinc chelate, and the optimum preparation conditions were obtained with mass ratio of FDEE to ZnSO4·7H2O of 25: 1, at pH 7.6 and 27.0 °C for 50 min. Structural analysis showed that both amino group and carboxyl group of FDEE were the main binding sites for zinc ions. FDEE-zinc chelate was relatively stable against incubation at 100 °C for 10–40 min and treatments of NaCl (1–2 g/100 g) and glucose (4 g/100 g). But long time thermal treatment or treatments of high content of NaCl (4 g/100 g) and glucose (8–12 g/100 g) significantly reduced zinc-solubility of FDEE-zinc chelate. Moreover, FDEE-zinc chelate showed higher zinc-solubility than ZnSO4 and zinc gluconate under pH 8.0–10.0 and gastrointestinal digestion (p < 0.05). In addition, peptide YILIK exhibited excellent antioxidant activity. The zinc-chelation improved hydroxyl radical scavenging activity and reducing power of FDEE (p < 0.05). Therefore, peptides identified in coconut globulin have potential usage as ingredients of zinc supplements or antioxidant in the food industry.