Antioxidant and sensory properties of protein hydrolysate derived from Nile tilapia (Oreochromis niloticus) by one- and two-step hydrolysis

Antioxidant and sensory properties of Nile tilapia protein hydrolysates prepared by one-and two-step hydrolysis using commercial proteases were investigated. Hydrolysates prepared using single protease including Alcalase (HA), Flavourzyme (HF), Protamex (HPr) and papain (HPa) had increases in antioxidant activities as the degree of hydrolysis (DH) increased up to 40 % (P<0.05). Amongst all hydrolysates, HA having 40 % DH showed the highest antioxidant activities. When HA was further hydrolysed by papain, the resulting hydrolysate (HAPa) exhibited the highest antioxidant activities for all assays tested (P<0.05). ABTS radical scavenging activity and metal chelating of HAPa generally remained constant in a wide pH range (1-11) and during heating at 30-100 degrees C. Both activities increased in the simulated gastrointestinal tract model system, especially in intestine condition. HAPa (100-1,000 ppm) could retard lipid oxidation in beta-carotene-linoleate and lecithin-liposome model systems in a dose dependent manner. Peptides in both HA and HAPa with molecular weight of 513 Da and 1,484 Da possessed the strongest ABTS radical scavenging activity and metal chelating activity, respectively. The amino acid profile of both HA and HAPa contained a high amount of hydrophobic amino acids (38.26-38.85 %) and had glutamic acid/glutamine, lysine and aspartic acid/asparagine as the dominant amino acids. However, HAPa showed a higher acceptability than did HA, owing to the lower bitterness. Therefore, the use of Alcalase in combination with papain for hydrolysis of protein isolate rendered the hydrolysate with antioxidant properties and reduced bitterness, which could serve as the functional supplement.