Revisiting the prospects of plastein: thermal and simulated gastric stability in relation to the antioxidative capacity of casein plastein.

Plastein, a product of protease-induced peptide aggregation, is thought to possess unique physical properties and bioactivity, although its formation, stability, and functional mechanisms remain unclear. This study demonstrates that plastein is formed from bovine casein peptides with Alcalase by hydrophobic and electrostatic interactions and less likely by covalent bonding. The peptide aggregation enhanced the Fe(III) reducing potential and decreased the Fe(II) chelating activity (p < 0.05) of casein peptides, but there was no difference in inhibition of Fe-induced linoleic acid peroxidation after plastein reaction. The casein plastein product retained its antioxidative activities after being heated at 100 °C. However, simulated gastric protease treatment with pepsin and pancreatic enzymes resulted in enhanced reducing potential and metal chelation of the casein plastein and reduction of the inhibitory effect on lipid peroxidation. It appears that the plasteins were disintegrated and further hydrolyzed by gastric proteases on the basis of the antioxidative capacity and RP-HPLC profile being similar to those of the casein hydrolysates. Therefore, plastein reaction may not confer metabolic stability or enhance the antioxidative capacity of casein peptides for prospective functional food applications.