The overall aim of this work was to characterise the major angiotensin-converting enzyme (ACE) inhibitory peptides produced by enzymatic hydrolysis of whey proteins, through the application of a novel integrative process. This process consisted of the combination of adsorption and microfiltration within a stirred cell unit for the selective immobilisation of β-lactoglobulin and casein-derived peptides (CDP) from whey. The adsorbed proteins were hydrolysed in situ, which resulted in the separation of peptide products from the substrate and fractionation of peptides. Two different hydrolysates were produced: (i) from CDP (IC(50)=287 μg/mL) and (ii) from β-lactoglobulin (IC(50)=128 μg/mL). The well-known antihypertensive peptide IPP and several novel peptides that have structural similarities with reported ACE inhibitory peptides were identified and characterised in both hydrolysates. Furthermore, the hydrolysates were assessed for bitterness. No significant difference was found between the bitterness of the control (milk with no hydrolysate) and hydrolysate samples at different concentrations (at, below and above the IC(50)).

The aim of this work is to develop an integrative process based on the use of an ion exchange resin for the enzymatic hydrolysis of b-lactoglobulin to produce peptides with angiotensin converting enzyme (ACE) inhibitory activity using whey as a feed stock. Unlike the conventional methods, the main advantage of this approach is that by integrating the selective separation of b-lactoglobulin from whey and its hydrolysis less complex mixtures of peptides are produced. Furthermore, peptides of similar charge as b-lactoglobulin remain adsorbed achieving further purification. In this work, the enzyme protease N Amano at an enzyme to substrate ratio of 1/100 (wt/wt) was added directly to the adsorbed proteins in a thermostatically controlled membrane reactor operated in batch mode. Separation of the smaller peptides from the enzyme and larger peptides was achieved with a 1 kDa molecular weight cut-off ultrafiltration membrane. Also, this step enables the recycling of nonhydrolyzed substrates, large peptides, and enzyme. The adsorbed protein was re-solubilised in a 10 mM potassium phosphate buffer (pH 7 and 45 C). The different fractions were assayed for their bioactivity in terms of angiotensin converting enzyme inhibition percentage (ACEi%) and IC 50 which is the concentration of peptides that can inhibit the ACE activity by 50%. Results show that permeates of 2 and 6 hrs hydrolysis have the highest bioactivity with IC 50 ¼ 67 and 98 lg=ml respectively.

Angiotensin I-converting enzyme (ACE) inhibition is one of the mechanisms by which reduction in blood pressure is exerted. Whey proteins are a rich source of ACE inhibitory peptides and have shown a blood pressure reduction effect i.e. antihypertensive activity. The aim of this work was to develop a simplified process using a combination of adsorption and microfiltration steps for the production of hydrolysates from whey with high ACE inhibitory activity and potency; the latter was measured as the IC50, which is the peptide concentration required to reduce ACE activity by half. This process integrates the selective separation of β-lactoglobulin- and casein-derived peptides (CDP) from rennet whey and their hydrolysis, which results in partially pure, less complex hydrolysates with high bioactive potency. Hydrolysis was carried out with protease N "Amano" in a thermostatically controlled membrane reactor operated in a batch mode. By applying the integrative approach it was possible to produce from the same feedstock two different hydrolysates that exhibited high ACE inhibition. One hydrolysate was mainly composed of casein-derived peptides with IC50=285 μg/mL. In this hydrolysate we identified the well-known potent ACE-inhibitor and antihypertensive tripeptide Ile-Pro-Pro (IPP) and another novel octapeptide Gln-Asp-Lys-Thr-Glu-Ile-Pro-Thr (QDKTEIPT). The second hydrolysate was mainly composed of β-lactoglobulin derived peptides with IC50=28 μg/mL. This hydrolysate contained a tetrapeptide (Ile-Ile-Ala-Glu) IIAE as one of the two major peptides. A further advantage to this process is that enzyme activity was substantially increased as enzyme product inhibition was reduced.

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