(2002) using RP-HPLC. Initially, a volume of 12.5 mL of the
substrate HHL (2.17 mM) was mixed with 50 mL of each
hydrolyzed WPC (10 mg/mL), both of which were prepared
with a 100 mM borate buffer, pH 8.3, containing 300 mM
NaCl, and the mixture was incubated at 37 °C for 10 min. A
volume of 200 mL of ACE (4 mU), prepared in the same
buffer, was subjected to a similar treatment. The two solutions
were subsequently mixed, and after incubation at 37
°C for 30 min, the reaction was stopped by the addition of
125 mL of HCl (1 mol/L). Next, the mixture was filtered
through a 0.22 mm membrane for analysis by RP-HPLC.
Standard solutions of HA, in concentrations ranging from
0.05 to 7.25 mmol/L, were also subjected to a similar treatment
to generate a standard curve.
For the analysis of ACE-IA, a GraceSmart RP-18 column
was used, and the HA and HHL were detected at 228 nm.
The elution flow rate was 0.5 mL/min with a two-solvent
system: (1) 0.05% trifluoroacetic acid (TFA) in water and
(2) 0.05% TFA in acetonitrile with a 5–60% acetonitrile gradient
for the first 10 min, 2 min at 60% acetonitrile and
1 min at 5% acetonitrile. This procedure was followed by
isocratic elution (A solvent) for 4 min at a constant flow
rate of 0.5 mL/min.
The ACE-IA was expressed as a percentage of inhibition
and as an IC50 value. IC50 is defined as the concentration of
hydrolysate (mg/mL) necessary to reduce the activity of
ACE by 50%.