Antioxidant activities and functional properties of grass carp (Ctenopharyngodon idellus) protein hydrolysates.

Background: Grass carp, with an annual production exceeding 4 × 10(6) t in China in 2009, has not been developed into a high-value product. In this study the antioxidant activities and functional properties of grass carp protein hydrolysates prepared with Alcalase 2.4L (HA) and papain (HP) were investigated. The hydrolysate with strongest radical-scavenging activity and reducing power was assessed further for changes in its antioxidant activity during simulated gastrointestinal digestion.

Results: As the degree of hydrolysis (DH) increased, the metal-chelating activity of both HA and HP increased while their reducing power and 1,1-diphenyl-2-picrylhydrazyl radical (DPPH(•) )-scavenging activity decreased (P < 0.05). At the same DH, HP possessed higher DPPH(•) -scavenging activity and reducing power than HA (P < 0.05). The metal-chelating activity of HP with 10% DH was significantly increased after in vitro gastrointestinal metabolism (P < 0.05). Regarding their functional properties, all hydrolysates were more than 81% soluble over a wide range of pH (3-8). At the same DH, HP showed higher emulsion activity index but lower solubility and foaming capacity than HA.

Conclusion: Grass carp protein hydrolysates showed high solubility over a wide pH range and could be used as natural antioxidants in food systems.