In vitro cytoprotection of modified casein hydrolysates by plastein reaction on rat hepatocyte cells

Casein hydrolysate of a degree of hydrolysis of 9.4% was generated from caseinate using papain and modified by plastein reaction with extrinsic phenylalanine or tyrosine addition, and then fractionated by an ethanol-water solvent (6:4, v/v). Compared to casein hydrolysate or mixtures of casein hydrolysate and phenylalanine or tyrosine, two modified hydrolysates prepared thereof showed higher scavenging activity on 2,2-diphenyl-1-picrylhydrazyl (DPPH) or hydroxyl radicals and reducing power. The obtained soluble and precipitated fractions had higher and lower total hydrophobic amino acids especially stronger and weaker three antioxidant properties than the parent substrates, respectively. All hydrolysates particularly soluble fractions protected rat hepatocytes against H2O2- or galactosamine-induced injury in vitro, resulting in enhanced cell viability, decreased cellular malondialdehyde content, and lactate dehydrogenase leakage. Cytoprotection of the hydrolysates was observed at a dosage-dependence manner. A negative correlation (P < 0.05) was found between malondialdehyde content and scavenging activity on hydroxyl radicals or reducing power of the hydrolysates.