The aim of this work was to produce antihypertensive protein hydrolysates through different forms of enzymatic hydrolysis (2% pepsin, 4% pepsin, 1% alcalase, 2% alcalase, 2% papain, and 2% pepsin + pancreatin) of hemp seed proteins (HSP). The hemp seed protein hydrolysates (HPHs) were tested for in vitro inhibitions of renin and angiotensin-converting enzyme (ACE), two of the enzymes that regulate human blood pressure. The HPHs were then administered orally (200 mg/kg body weight) to spontaneously hypertensive rats and systolic blood pressure (SBP)-lowering effects measured over a 24 h period. Size exclusion chromatography mainly showed a 300–9560 Da peptide size range for the HPHs, while amino acid composition data had the 2% pepsin HPH with the highest cysteine content. Fluorescence spectroscopy revealed higher fluorescence intensities for the peptides when compared to the unhydrolyzed hemp seed protein. Overall, the 1% alcalase HPH was the most effective (p < 0.05) SBP-reducing agent (−32.5 ± 0.7 mmHg after 4 h), while the pepsin HPHs produced longer-lasting effects (−23.0 ± 1.4 mmHg after 24 h). We conclude that an optimized combination of the fast-acting HPH (1% alcalase) with the longer-lasting HPHs (2% and 4% pepsin) could provide daily effective SBP reductions.

This report shows the antioxidant effects of a hemp seed meal protein hydrolysate (HMH) in spontaneously hypertensive rats (SHR). Defatted hemp seed meal was hydrolyzed consecutively with pepsin and pancreatin to yield HMH, which was incorporated into rat feed as a source of antioxidant peptides. Young (8-week old) SHRs were divided into three groups (8 rats/group) and fed diets that contained 0.0%, 0.5% or 1.0% (w/w) HMH for eight weeks; half of the rats were sacrificed for blood collection. After a 4-week washout period, the remaining 20-week old SHRs were fed for an additional four weeks and sacrificed for blood collection. Plasma total antioxidant capacity (TAC) and superoxide dismutase (SOD), catalase (CAT) and total peroxides (TPx) levels were determined. Results showed that plasma TAC, CAT and SOD levels decreased in the older 20-week old SHRs when compared to the young SHRs. The presence of HMH in the diets led to significant (p < 0.05) increases in plasma SOD and CAT levels in both young and adult SHR groups; these increases were accompanied by decreases in TPx levels. The results suggest that HMH contained antioxidant peptides that reduced the rate of lipid peroxidation in SHRs with enhanced antioxidant enzyme levels and total antioxidant capacity.

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.