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Ile–Trp (IW) and Trp–Leu (WL) are present in enzymatic hydrolysates of whey proteins and act as efficient inhibitors for angiotensin-converting enzyme (ACE) in vitro. Baseline plasma concentrations of IW and WL were analysed to 0.9 ± 0.3 n m for IW and 8.3 ± 1.3 n m for WL. Following administration of 50 mg IW or 100 mg WL to human volunteers (n = 3 for IW and n = 2 for WL, respectively), a significant increase in plasma concentrations to a maximum of 2.4 ± 0.5 n m for IW and 29–36 n m for WL after 0.5 h was observed, followed by rapid elimination. ACE activity in plasma decreased by 32% ± 8% following 50 mg IW administration. Administration of the corresponding amino acids had no effect on ACE activity. Thus, these tryptophan-containing dipeptides may serve as bioactive food additives with beneficial effects for the cardiovascular system.

Enzymatic hydrolysis of proteins from rice, soy, pea and wheat, with both chymotrypsin and thermolysin, resulted in hydrolysates, which are efficient inhibitors of the angiotensin-converting enzyme (ACE). IC50 values of the hydrolysates were between 27 and 39mg/l, which is comparable to enzymatically hydrolysed whey protein. A significant increase of the ACE-inhibiting effect was observed following butanol extraction due to accumulation of hydrophobic peptides (IC50 between 12 and 21mg/l). Based on the identification and quantification of individual tryptophan-, tyrosine- and phenylalanine-containing dipeptides, 50-80% of the total ACE-inhibiting potential of butanol extracts from plant protein hydrolysates could be explained. Compared to hydrolysates from whey protein, where the inhibitory effect can almost exclusively be attributed to Ile-Trp, the ACE inhibition by plant protein hydrolysates is caused by a variety of peptides, in particular tyrosine-containing peptides. Hydrolysates of plant proteins are promising ingredients for the development of functional foods.

Bioactive peptides such as Ile-Trp show great potential as natural ACE (angiotensin-converting-enzyme)-inhibitors. A continuous process for the up-scaled enrichment of ACE-inhibiting peptides based on a columnar adsorber system with an activated carbon stationary phase was developed. The particle size of the adsorbent and the flow rate was investigated as key factors affecting adsorption kinetics and separation performance. Batch and column adsorption experiments of model adsorbate systems were successfully transferred to a more complex system of an α-lactalbumin hydrolysate containing a multitude of species. Ile-Trp was successfully enriched from the hydrolysate by a factor of 4 using the optimized carbon column. The enrichment was more selective using smaller adsorbent particles due to improved adsorption kinetics.