Angiotensin-I converting enzyme (ACE), which encourages conversion
of angiotensin-I to angiotensin-II, acts an important physiological
role in regulating blood pressure. ACE inhibitory peptides
can restrain theactivityofACEandhavebeenshown tobeefficient
in lowering blood pressure in animal models and patients.1 It has
been reported that numbers of ACE inhibitory peptides have been
derived fromvarious food proteins by enzymatic hydrolysis or fermentation,
such as tilapia,2 jellyfish,3 wheat germ,4 rice,5 pea,6 sea
bream,7 cuttlefish,8 lizard fish1 and thornback ray.9
The production of ACE inhibitory peptides is traditionally
performed using a three-step procedure including extraction,
hydrolysis and separation. In terms of separation, the methods
used for peptide fractionation and enrichment are ion exchange,
gel filtration technologies3 and liquid chromatography.10 Nevertheless,
these methods cannot be employed for mass production
scale.11 Alternatively, ultra-filtration (UF) using membranes with
low molecular weight cut-off (MWCO) has been found useful for
separating small peptides from high molecular weight residues.12
It is known that UF is considered to be of tremendous importance
for concentration, purification and fractionation of various
products in diverse fields such as food, pharmaceutical, and
biotechnological industries.13 Nowadays, UF provides one of the
promising technologies available for enrichment of high-quality
ACE inhibitor peptides delivered from various protein sources
such as potato,14 tilapia,2 cottonseed,15 green algae,16 and spent
grain.17 Picot et al.18 found that UF was able to fractionate bioactive
peptides from fish protein hydrolysate. This study also suggested