Effect of digestive enzymes on antimicrobial, radical scavenging and angiotensin I-converting enzyme inhibitory activities of camel colostrum and milk proteins
Camel milk and colostrum are known to be a rich source of bioactive proteins. Camel milk, colostrum and colostral whey proteins were successively hydrolysed by pepsin and pancreatin using an in vitro protocol mimicking gastro-intestinal digestion. The degradation of proteins was characterised by electrophoresis and reversed-phase ultra-high performance liquid chromatography. Two whey proteins, α-lactalbumin and immunoglobulins G, were more resistant to the digestive proteolytic enzymes than other camel milk and colostrum proteins. Undigested and digested samples were assayed for their antioxidant, angiotensin I-converting enzyme inhibitory and antimicrobial properties. Camel colostrum, colostral whey and milk proteins had unveiled angiotensin I-converting enzyme (ACE) inhibitory activity following in vitro enzymatic digestion and a higher free radical scavenging activity than before their digestion. Moreover, Escherichia coli XL1 blue and Listeria innocua LRGIA01 cells growth were both inhibited by undigested and digested samples, suggesting that antimicrobial proteins resisted to the action of digestive enzymes or that antimicrobial fragments of camel milk and colostrum proteins were released or both. After pepsin and pancreatin hydrolysis, camel milk and colostrum proteins digests still had an antibacterial activity and their antioxidative and ACE-inhibitory activity even increased, suggesting that bioactive fragments of camel milk and colostrum proteins such as antioxidative and ACE-inhibitory peptides were released. Among 181 peptides identified by tandem mass spectrometry, 25 were homologous to known bioactive peptides, particularly with ACE inhibitors and free radical scavengers.
KeywordsAngiotensin I-converting enzyme inhibition Antibacterial activity Antioxidant activity Camel colostrum proteins Camel milk proteins Digestive enzymes
The authors would like to acknowledge the Ministère des Affaires Etrangères (France) for supporting Dr Halima El Hatmi’s stays (SSHN grants) in BioDyMIA (Université Lyon 1, France) and UR AFPA (Université de Lorraine, France) laboratories. The authors also thank IRA (Medenine, Tunisia) and University of Gabes (Tunisia) for supporting Mrs Zeineb Jrad’s stay in BioDyMIA laboratory, Dr Faïza Zidane (UR AFPA) for her good advices in the ACE-inhibitory activity assays and Mrs Claire Soligot-Hognon (UR AFPA) for technical assistance in UHPLC.
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