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UBC Theses and Dissertations

Effects of exopeptidase treatment on angiotensin I-converting enzyme inhibitory activity, antihypertensive activity and taste of whey protein hydrolysates Cheung, Lennie Ka Yan


Hypertension is commonly treated with angiotensin I-converting enzyme (ACE) inhibitors. Synthetic ACE inhibitors are associated with adverse side effects while ACE inhibitors sourced from food protein hydrolysates are not. Protein hydrolysates have potential use as functional food ingredients, but often have bitter taste. Since terminal amino acids are implicated to cause peptide bitterness, hydrolysates can be debittered when treated with enzymes such as exopeptidases, which release N- or C-terminal amino acids (aminopeptidases or carboxypeptidases, respectively) from peptides to produce shorter peptides and free amino acids. However, exopeptidase treatment may influence peptide ACE-inhibitory activity as well. Thus, this study aimed to determine the effects of exopeptidase treatment on ACE-inhibitory activity, antihypertensive activity and taste of a whey protein hydrolysate (WPH). A Thermoase PC10F-produced WPH (T3) with high ACE-inhibitory activity (IC₅₀ = 0.15 mg/mL) was treated with the carboxypeptidase Accelerzyme® CPG (T3-AC7), the aminopeptidase Peptidase R (T3-PR7), or the aminopeptidase and proteinase ProteAX (T3-PX7). The three exopeptidase-treated hydrolysates exhibited high ACE-inhibitory activities (IC₅₀ = 0.24–0.34 mg/mL). All size fractions of T3, obtained using size exclusion chromatography, exhibited relatively high ACE-inhibitory activity while the 200–1000 Da fractions of exopeptidase-treated hydrolysates exhibited the highest activity. All hydrolysates lowered systolic blood pressure (maximum reductions of 30–35 mm Hg) in spontaneously hypertensive rats (SHRs) for 24 h after a single dose of 100 mg/kg body weight. In terms of taste, the exopeptidase-treated hydrolysates were found to have significantly lower bitterness than T3 when evaluated by a trained sensory panel (n = 12), with T3-AC7 and T3-PR7 having bitterness similar to a commercial WPH without ACE-inhibitory activity. The three exopeptidase-treated hydrolysates also had higher umami taste and saltiness than T3, which may be partly explained by the release of free amino acids. Bitterness correlated negatively with overall acceptability, emphasizing the importance of debittering hydrolysates prior to their use as food ingredients. The WPH treated with either aminopeptidase or carboxypeptidase in this study was significantly debittered and still exhibited ACE-inhibitory activity in vitro and antihypertensive activity in SHRs. Exopeptidase treatment, therefore, has potential use for debittering antihypertensive hydrolysates prior to their incorporation into functional foods.

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