Release of Angiotensin I-Converting Enzyme Inhibitory Peptides from Flaxseed (Linum usitatissimum L.) Protein under Simulated Gastrointestinal Digestion

January 1, 2011 Human Health and Nutrition Data 0 Comments

Release of Angiotensin I-Converting Enzyme Inhibitory Peptides from Flaxseed (Linum usitatissimum L.) Protein under Simulated Gastrointestinal Digestion

Year: 2011
Authors: Marambe, H.K. Shand, P.J. Wanasundara, J.P.D.
Publication Name: Journal of Agricultural and Food Chemistry
Publication Details: Volume 59, Pages 9596-9604.


The scope of this study was to determine the ability of flaxseed (Linum usitatissimum L.) proteins to release angiotensin I-converting enzyme inhibitory (ACEI) peptides during simulated gastrointestinal (GI) digestion using a  static (SM; no absorption in the intestinal phase) and a dynamic model (DM; simultaneous absorption of digested products in the intestinal phase via passive diffusion). Gastric and gastric + small intestinal digests of flaxseed proteins of both models possessed ACEI activity. The ACEI activity of the gastric + small intestinal digest in the DM (IC50 unabsorbed, 0.05 mg N/mL; IC50 absorbed, 0.04 mg N/mL) was significantly higher (p < 0.05) than that of the SM (IC50, 0.39 mg N/mL). Two peptides, alpha pentapeptide (Trp-Asn-Ile/Leu-Asn- Ala) and a hexapeptide (Asn-Ile/Leu-Asp-Thr-Asp-Ile/Leu) were identified in the most active ACEI fraction (0.51 kDa) of the absorbable flaxseed protein digest by de novo sequencing. (Author's Abstract)
The authors speculate that the anti-atherogenic effects of defatted flaxseed meal suggest that non-lipids component in flaxseed meal could contributory factors for protection against CVD. Flaxseed proteins have received very limited attention as a potential component with significant biological activity. Peptides with angiotensin I-converting enzyme inhibitory (ACEI) activities are key molecules to reduce elevated blood pressure. The presence of ACEI activity in enzymatically hydrolyzed flaxseed protein in vitro has been reported by previous studies. To date, there are no published information available on the ability of flaxseed protein to generate ACEI peptides during GI digestion either in vitro or in vivo. Also, flaxseed protein derived ACEI peptides have not been sequenced. The objective of the present in vitro study was to investigate whether flaxseed protein generates ACEI peptides with the potential for absorption during simulated GI digestion. Flaxseed protein was subjected to simulated GI digestion using a static model (SM; no absorption of digested products) and a dynamic model (DM; simulated absorption via passive diffusion) for comparison purposes. The amino acid pattern of flaxseed protein was reported to be comparable to that of soy, with relatively high contents of Asp, Glu, Leu, and Arg. The results also suggested that flaxseed protein could be anti-atherogenic and can contribute significantly to the supply of essential amino acids in the diet. The ratio of Lys to Arg of the extracted flaxseed protein (0.22) was lower as compared to that of proteins of soy and canola (0.88 for both).  Arg, which is the substrate of nitric oxide synthase (NOS), generates nitric oxide (NO) that acts as a vasodilator and an inhibitor of platelet aggregation. A low Lys:Arg is suggested to have anti-atherogenic effect and anti-thrombotic effects of many plant proteins, which indicates a higher potential of flaxseed protein to deliver anti-atherogenic and antithrombotic effects than soy or canola proteins. Gastric digest as well as the gastric + small intestinal digest of flaxseed protein obtained using both SM and DM showed ACEI activity exhibiting the ability of flaxseed protein to release ACEI peptides during GI digestion.  The IC50 gastric + small intestinal digest (SM) of flaxseed protein was within the range reported for GI digested whey protein (0.35+/-1.73 mg/mL). Further studies are needed to validate the ACEI activity of flaxseed peptides. The present simulated GI digestion study showed that flaxseed protein generates peptides with ACEI activity, which may absorb via the intestinal epithelium, suggesting that the protein in flaxseed can contribute to its cardioprotective function. The authors caution that results of studies on bioactive peptide release during GI digestion obtained from the in vitro static digestion models may be underestimated. (Editor's comments)

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