Angiotensin I‐converting enzyme inhibitory and Ca‐binding activities of peptides prepared from tuna cooking juice and spleen proteases

Tuna cooking juice is a by‐product from the tuna canning industry. In this study, tuna cooking juice was hydrolysed by proteases extracted from the spleen. Tuna cooking juice showed the highest ACE inhibitory and Ca‐binding activities after hydrolysis for 270 and 180 min, respectively. The hydrolysate was further fractionated by ultrafiltration. The permeate exhibited highest ACE inhibitory and Ca‐binding activities when passed through 1 and 5 kDa cut‐off membranes, respectively. Gel filtration chromatography was used to determine the MW of bioactive peptides that exhibited highest ACE inhibitory and Ca‐binding activities. Those peptides that exhibited highest ACE inhibitory and Ca‐binding activities were the MW range of 238–829 Da and 1355–1880 Da, respectively. These results suggest that the tuna cooking juice and the spleen protease extract are a potential source of bioactive peptides that can be utilised as bioactive ingredients in functional food and nutraceuticals.     

Calcium-binding peptides derived from tilapia (Oreochromis niloticus) protein hydrolysate

Calcium-binding peptide was derived from protein hydrolysates. In this study, tilapia protein at a concentration of 2 % (w/v) was hydrolyzed using various proteases including Alcalase 2.4 L, Flavourzyme 1,000L, Protease GN, and papain at 50 °C, pH 8 for 6 h. It was found that the degree of hydrolysis increased with the time of the incubation in all cases. The highest calcium-binding capacity of the hydrolysate was 65 mg/g protein at 27.7 % degree of hydrolysis by Alcalase 2.4 L. The molecular weight of the calcium-binding peptides characterized by gel-filtration chromatography on a Sephadex G-25 was 1.2 kDa. The calcium-binding motif of the hydrolyzed peptides identified by the automated Edman degradation was a short peptide (Trp-Glu-Trp-Leu-His-Tyr-Trp). The results of this study suggested that tilapia protein is a good source for calcium-binding peptides.