Antioxidant and Angiotensin Converting Enzyme-Inhibitory Properties of a Flaxseed Protein-Derived High Fischer Ratio Peptide Mixture

January 1, 2010 Human Health and Nutrition Data 0 Comments

Antioxidant and Angiotensin Converting Enzyme-Inhibitory Properties of a Flaxseed Protein-Derived High Fischer Ratio Peptide Mixture

Year: 2010
Authors: Udenigwe, C.C. Aluko, R.E.
Publication Name: Journal of Agricultural and Food Chemistry
Publication Details: Volume 58; Pages 4762-4768


Hydrolysis of flaxseed proteins using thermolysin and pronase followed by mixing with activated carbon, centrifugation and filtration yielded a filtrate (peptide mixture) with a Fischer ratio (branchedchain amino acids/aromatic amino acids) of 23.65 and a phenylalanine-tyrosine content of 1.11%. Gel permeation chromatography showed that the flaxseed peptide sample contained mainly low molecular weight peptides (<4 kDa). The high Fischer ratio peptide sample exhibited antioxidant property by scavenging 2,2-diphenyl-1-picrylhydrazyl radical, superoxide radical, hydroxyl radical, and also by protecting linoleic acid from oxidation. In addition, the peptide mixture showed potential antihypertensive properties by inhibiting angiotensin I-converting enzyme in a mixed-type inhibition pattern. Protein hydrolysates with Fischer ratio higher than 20 and phenylalanine- tyrosine content lower than 2% have been used to treat patients with hepatic encephalopathy; thus, this multifunctional flaxseed peptide mixture could be used to formulate food products with multiple human health benefits during liver diseases, oxidative stress and hypertension. (Author's abstract)
Plasma amino acid imbalance has been found in patients with liver diseases, and this is characterized by elevated levels of aromatic amino acids (AAA; tyrosine and phenylalanine) and methionine, and decreased levels of branched-chain amino acids (BCAA; leucine, isoleucine and valine). The ratio of plasma BCAA to AAA is termed Fischer ratio and is used to measure abnormal amino acid metabolism during liver disease. In human beings, the normal plasma Fischer ratio is 3.5-4.0; this value decreases to <2.5 in liver diseases, <1.2 in hepatic coma and could drop to below 0.8 in profound coma. A number of studies have reported successful production of high Fischer ratio peptide mixtures by enzymatic hydrolysis of food proteins and subsequent processing using activated carbon and gel filtration chromatography.  Proteins constitute a major part of defatted flaxseed meal,  and is comparable in nutritional quality and amino acid composition to other high quality proteins, e.g. soy protein. Flaxseed proteins contain high levels of BCAA, with 50, 71, and 56 mg/g of isoleucine, leucine and valine, respectively, and thus have the potential to be converted into protein hydrolysates enriched with BCAA. The renin-angiotensin system, which controls blood pressure in human beings, has been targeted for the treatment of hypertension through the inhibition of angiotensin I-converting enzyme (ACE) and renin. ACE inhibitors possess the ability to lower blood pressure. A BCAA-enriched product that possesses other bioactive properties could, in addition to the positive effects on liver disease, provide relief from other associated disease symptoms. The objectives of this project were to produce a high Fischer ratio enzymatic flaxseed protein hydrolysate and determine the ability of the hydrolysate to scavenge free radicals and inhibit in vitro oxidative reactions and activities of ACE and renin. Enzymatic hydrolysis of flaxseed protein in this study was used to produce peptides with low contents of AAA and generate low-MW peptides for efficient intestinal absorption. The authors describe the utilization of several methods to produce the highest Fischer ratio flaxseed peptide mixture from thermolysin-pronase treatment. This product may have promise for use in treating liver diseases. The high Fischer ratio peptide mixture produced in this work showed antioxidant activity which could offer protection to cellular components. The BCAA-rich sample also displayed potential antihypertensive property as evident from the concentration dependent inhibition of ACE activity with up to 70.8% ACE inhibition at 0.4mg/mL and 50% inhibitory concentration (IC50) value of 0.16 ( 0.0055 mg/mL). The authors conclude that treatment of flaxseed protein isolate with thermolysin and pronase followed by simple mixing with activated carbon produced a BCAA-rich mixture with high Fischer ratio.  Animal feeding experiments using this BCAA-rich sample preparation in animal model of liver disease will be conducted to evaluate the in vivo effects of the peptides in improving plasma Fischer ratio and reducing muscle wasting. (Editor's comments)

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