Journal of Dairy Research

Yak Milk Casein as a Functional Ingredient: Preparation and Identification of Angiotensin-I-Converting Enzyme Inhibitory Peptides 1

Jingli Jiang a1, Shangwu Chen a1, Fazheng Ren a1a2c1, Zhang Luo a3 and Steve S Zeng a4
a1 College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
a2 Key Laboratory of Functional Dairy of Chinese Ministry of Education, Beijing 100083, China
a3 College of Agricultural and Animal Husbandry, Tibet University, Tibet 850000, China
a4 School of Agriculture & Applied Sciences, Langston University, Oklahoma 73050, USA

Article author query
jiang j   [PubMed][Google Scholar] 
chen s   [PubMed][Google Scholar] 
ren f   [PubMed][Google Scholar] 
luo z   [PubMed][Google Scholar] 
zeng ss   [PubMed][Google Scholar] 


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.