Abstract:

In this study, we evaluated the immune activity of ultrafiltration components from yellowfin tuna (Thunnus albacares) meat hydrolyzed by four different proteases on RAW264.7 cells. The RAW264.7 cell line was used as the cell activity screening model in vitro. Methyl thiazolyl tetrazolium (MTT), neutral red and Griess reagent methods were used to detect cell activity, phagocytosis capability and nitric oxide levels in cell culture medium. The amino-acids composition and molecular weight distribution of the hydrolysate were also analyzed. The results show that trypsin hydrolysate had no obvious cytotoxicity in the range of 12.5-200 μg·mL^-1 for RAW264.7 cells. It could enhance the phagocytic capacity, and reached the maximum value of 132.50% (P<0.01) at the concentration of 400 μg·mL^-1. In the concentration range of 50-200 μg·mL ^-1, the trypsin hydrolysate could promote nitric oxide release of macrophages (P<0.01), and there was a dose-effect relationship between NO release and the concentration of enzymolysis solution. The content of essential amino acid (EAA, 51.09%) of trypsin hydrolysate was higher than those of the other enzymatic hydrolysates, and the contents of histidine (His, 11.59%), lysine (Lys, 11.00%) and arginine (Arg, 6.90%) were also higher than those of the other enzymatic hydrolysates. The content of small peptides with molecular weight less than 1k Da was as high as 97.48% in trypsin hydrolysate. In the four protease hydrolysates, the 3k Da peptide fraction of trypsin hydrolysate of tuna meat had obvious immune activity, which provides a theoretical basis for its development and utilization as a functional ingredient.

Key words: Thunnus albacares, polypeptide, immunomodulatory activity, amino acid