*2.2. ACE Inhibitory Activity Assay*

ACE inhibitory activity of phenolic acids was determined according to the method reported by Cushman and Cheung (1971), using ACE (0.1 U/mL) and hippuryl-His-Leu (5 mM) [17]. The absorbance was measured at 228 nm using a spectrophotometer (BioTek, Inc., Winooski, VT, USA). Captopril was used as a positive control. The inhibition rate was calculated using the following formula.

$$\text{ACE inhibition rate (\%)} = \text{(OD}\_{\text{control}} - \text{OD}\_{\text{sample}}) / \text{OD}\_{\text{control}} \times 100$$

#### *2.3. Cell Culture and Sample Treatment*

EA.hy 926 cells were incubated in DMEM supplemented with 10% FBS at 37 ◦C in humidified air with 5% CO2. Endothelial cells were seeded at a density of 6 × 105 cells/mL in a 96-well plate. The cells were pre-treated with a serum-free medium containing 50 μM phenolic acids for 1 h and then exposed to 600 μM H2O2 with phenolic acids for 24 h. Cell cytotoxicity was determined using a thiazolyl blue tetrazolium bromide reagent.
