Identification and characterization of metal‐chelating bioenhancer peptide derived from fermented Citrullus lanatus seed milk

In the present investigation, a metal-chelating bioactive peptide was derived from Citrullus lanatus seed milk fermented with Lactococcus lactis. The cationic fermented milk peptide (FMP) thus obtained was purified using the HiTrap-chelating column followed by rpHPLC. The FMP possessed the ability to chelate multiple divalent cations like Cu2+ , Ca2+ , and Fe2+ with 86.81%, 61.04%, and 24.32% of chelation respectively and further it exhibited 78.03% of DPPH free radical scavenging activity. Interaction of FMP with metal ions was assessed by change in the absorption spectra and was analyzed by ultraviolet-visible and fluorescence spectroscopy. The FMP-metal complexes were found stable at simulated gastric conditions. In vitro analysis using intestinal Caco-2 cell lines revealed that there was an increase in metal bioavailability in the presence of the FMP and was least influenced by the addition of a dietary inhibitor, phytic acid. By LC-MS analysis the molecular mass of FMP was found to be 11.6 kD and it contains oxygen-rich and nitrogen-rich amino acids that favor the metal chelation. In our study, we have found that the fermented C. lanatus seed milk can serve as a potential functional food with bioenhancer peptides that increase metal bioavailability and enhance human health. PRACTICAL APPLICATIONS: Chelated metals are preferred over non-chelated ones by most nutritionists for their better absorption rate. Chelation protects the minerals from the digestive process and increases their bioavailability. Fermentation with lactic acid bacteria produces bioactive peptides with metal-chelating and antioxidant ability which provides additional health benefits beyond supplying basic nutrients. Lactococcus lactis fermented milk acts as a probiotic product with bioenhancer peptide that increases mineral bioavailability. Consumption of metals in chelated form can reduce excess intake of metal. Fermented watermelon seed milk can be a promising probiotic drink rich in bioenhancer peptides and can enhance the bioavailability of divalent cations of a high therapeutic index.