Thermoase-Derived Flaxseed Protein Hydrolysates and Membrane Ultrafiltration Peptide Fractions Have Systolic Blood Pressure-Lowering Effects in Spontaneously Hypertensive Rats

Abstract

Thermoase-digested flaxseed protein hydrolysate (FPH) samples and ultrafiltration membrane-separated peptide fractions were initially evaluated for in vitro inhibition of angiotensin I-converting enzyme (ACE) and renin activities. The two most active FPH samples and their corresponding peptide fractions were subsequently tested for in vivo antihypertensive activity in spontaneously hypertensive rats (SHR). The FPH produced with 3% thermoase digestion showed the highest ACE- and renin-inhibitory activities. Whereas membrane ultrafiltration resulted in significant (p < 0.05) increases in ACE inhibition by the <1 and 1–3 kDa peptides, only a marginal improvement in renin-inhibitory activity was observed for virtually all the samples after membrane ultrafiltration. The FPH samples and membrane fractions were also effective in lowering systolic blood pressure (SBP) in SHR with the largest effect occurring after oral administration (200 mg/kg body weight) of the 1–3 kDa peptide fraction of the 2.5% FPH and the 3–5 kDa fraction of the 3% FPH. Such potent SBP-lowering capacity indicates the potential of flaxseed protein-derived bioactive peptides as ingredients for the formulation of antihypertensive functional foods and nutraceuticals.

Antioxidant Properties of Flaxseed Protein Hydrolysates: Influence of Hydrolytic Enzyme Concentration and Peptide Size

“…The FPI suspension was heated to 37 °C and adjusted to pH 8.0 with 0.5 M NaOH. Thermoase GL‐30 was added at 2.5 or 3.0% (based on FPI protein weight) as previously described (Nwachukwu et al, ). Following enzyme addition, the protein digestion was performed for 4 hours with temperature and pH maintained constant using a thermostat‐equipped hotplate and periodic addition of 0.5 M NaOH, respectively.…”

“…However, in addition to their nutritional value, recent works have indicated the potential use of flaxseed proteins as sources of bioactive peptides, such as angiotensin‐converting enzyme inhibitors and free radical scavengers (Marambe, Shand, & Wanasundara, ; Marambe, Shand, & Wanasundara, ; Udenigwe & Aluko, ). The multifunctional nature of flaxseed protein‐derived peptides is also evident in studies that have demonstrated potential health‐promoting functions, such as antimicrobial (Hwang, Chen, Luo, & Chiang, ), antihypertensive (Doyen et al, ; Nwachukwu, Girgih, Malomo, Onuh, & Aluko, ), calmodulin‐inhibiting (Udenigwe & Aluko, ), anti‐inflammatory (Udenigwe, Lu, Han, Hou, & Aluko, ), antioxidant (Hwang et al, ; Udenigwe, Lu, et al, ), and antidiabetic (Doyen et al, ) properties. Thus, flaxseed protein‐derived peptides can serve as useful ingredients in the production of functional foods and nutraceuticals targeted at preventing and/or delaying the onset of certain human diseases.…”

“…Flaxseed protein‐derived peptides have also demonstrated inhibitions of calmodulin‐dependent phosphodiesterase (Udenigwe & Aluko, ) and nitric oxide synthases (Omoni & Aluko, ; Omoni & Aluko, ). In addition, oral administration of flaxseed protein hydrolysates (FPH) to spontaneously hypertensive rats led to blood pressure reductions (Doyen et al, ; Nwachukwu et al, ). However, there is scant information on the potential use of ultrafiltration to enhance the antioxidant properties of flaxseed protein‐derived peptides.…”

“…Moreover, fundamental scientific information on the potential role of amino acid sequence in the antioxidant properties of flaxseed peptides is lacking. In our initial work (Nwachukwu et al, ), FPH were produced using 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0% thermoase concentrations followed by the determination of antihypertensive properties. We found that the 2.5 and 3.0% peptide fractions possessed the strongest blood pressure‐reducing properties.…”

Food protein-derived renin-inhibitory peptides:in vitroandin vivoproperties

“…The results can be interpreted to mean that optimum peptide sizes were produced with the 1% enzyme dose whereas at higher doses, some of the active peptides may have been further hydrolyzed, which reduced renin‐inhibitory ability. In contrast, the renin‐inhibitory activity of flaxseed protein hydrolyzates was increased at higher protease concentrations (Nwachukwu, Girgih, Malomo, Onuh, & Aluko, ). Differences could be due to the lack of similarity between the amino acid composition of chicken skin and flaxseed as well as the specificity of proteases used, both of which would have led to production of peptides that have no common amino acid sequences.…”