Yak Milk Casein as a Functional Ingredient: Preparation and Identification of Angiotensin-I-Converting Enzyme Inhibitory Peptides 1
Yak milk casein derived from Qula, a traditional Tibetan acid curd cheese, was hydrolyzed by six commercially available proteases (Trypsin, Pepsin, Alcalase, Flavourzyme, Papain and Neutrase). These hydrolysates were assayed for their inhibitory activity of Angiotensin-I-converting enzyme (ACE). The hydrolysates obtained by Neutrase from Bacillus amyloliquefaciens showed the highest ACE inhibitory activity. The IC50 value of Neutrase-hydrolysate was 0·38 mg/ml. The hydrolysate obtained by Neutrase was further separated by consecutive ultra-filtration with 10 kDa and then with 6 kDa molecular weight cut-offs into different permeated parts and fractionated by gel filtration chromatography with a Sephadex G-25 column. The active fraction was subjected to RP-HPLC, in which five peaks were purified and identified. Amino acid sequence analysis confirmed that the peptides and origins were as follows: YQKFPQY (αs2-CN; f89–95), LPQNIPPL (β-CN; f70–77), SKVLPVPQK (β-CN; f168–176), LPYPYY (κ-CN; f56–61) and FLPYPYY (κ-CN; f55–61). Their amino acid sequences matched well with those of known bioactive peptides from bovine casein. The results indicated that yak milk casein could be a resource to generate antihypertensive peptides and be used as multifunctional active ingredients for many value-added functional foods as well as a traditional food protein.(Received October 7 2005)
(Accepted May 24 2006)
(Published Online September 21 2006)
Key Words: Angiotensin-I-converting enzyme; ACE inhibitory peptide; Qula; yak milk casein.
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1 Abbreviations: ACE, Angiotensin-I-converting enzyme; FAPGG, 2-Furanacryloyl-1-Phe-Gly-Gly; DH, degree of hydrolysis; IC50, inhibitory concentration that inhibits 50% of ACE activity; MWCO, molecular weight cut-off; RP-HPLC, reversed-phase high performance liquid chromatography; ESI-MSn, Electrospray Ionization Tandem Mass Spectrometry.