BACKGROUND: Membrane fouling is a major problem in ultra-filtration systems and two-phase flow is a promising technique
for permeate flux enhancement. The objective of this research was to study the use of an ultra-filtration (UF) system to enrich
angiotensin-I converting enzyme (ACE) inhibitory peptides from tilapia protein hydrolysate. To select the most appropriate
membrane and operating condition, the effects ofmembranemolecularweight cut-off(MWCO), transmembrane pressure (TMP)
and cross-flowvelocity (CFV) on permeate flux and ACE inhibitory peptide separationwere studied. Additionally, the gas–liquid
two-phase flow technique was applied to investigate its effect on the process capability.
RESULTS: The results showed that the highest ACE inhibitory activity was obtained from permeate of the 1 kDa membrane. In
termsof TMPandCFV, thepermeatefluxtended toincreasewith TMPandCFV. The useofgas–liquid two-phaseflowas indicated
by shear stress number could reduce membrane fouling and increase the permeate flux up to 42%, depending on shear stress
number. Moreover, the use of a shear stress number of 0.039 led to an augmentation in ACE inhibitory activity of permeates.
CONCLUSIONS: Operating conditions using a shear stress number of 0.039were recommended for enrichment of ACE inhibitory
peptides.